drivers/gpu/drm/drm_dp_mst_topology.c

/*
 * Copyright © 2014 Red Hat
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 */

#include <linux/bitfield.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/iopoll.h>

#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
#include <linux/stacktrace.h>
#include <linux/sort.h>
#include <linux/timekeeping.h>
#include <linux/math64.h>
#endif

#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_dp_mst_helper.h>
#include <drm/drm_drv.h>
#include <drm/drm_print.h>
#include <drm/drm_probe_helper.h>

#include "drm_crtc_helper_internal.h"
#include "drm_dp_mst_topology_internal.h"

/**
 * DOC: dp mst helper
 *
 * These functions contain parts of the DisplayPort 1.2a MultiStream Transport
 * protocol. The helpers contain a topology manager and bandwidth manager.
 * The helpers encapsulate the sending and received of sideband msgs.
 */
struct drm_dp_pending_up_req {
	struct drm_dp_sideband_msg_hdr hdr;
	struct drm_dp_sideband_msg_req_body msg;
	struct list_head next;
};

static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
				  char *buf);

static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);

static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
				     int id,
				     struct drm_dp_payload *payload);

static int drm_dp_send_dpcd_read(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_mst_port *port,
				 int offset, int size, u8 *bytes);
static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
				  struct drm_dp_mst_port *port,
				  int offset, int size, u8 *bytes);

static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
				    struct drm_dp_mst_branch *mstb);

static void
drm_dp_send_clear_payload_id_table(struct drm_dp_mst_topology_mgr *mgr,
				   struct drm_dp_mst_branch *mstb);

static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
					   struct drm_dp_mst_branch *mstb,
					   struct drm_dp_mst_port *port);
static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
				 u8 *guid);

static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port);
static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port);
static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);

static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
						 struct drm_dp_mst_branch *branch);

#define DBG_PREFIX "[dp_mst]"

#define DP_STR(x) [DP_ ## x] = #x

static const char *drm_dp_mst_req_type_str(u8 req_type)
{
	static const char * const req_type_str[] = {
		DP_STR(GET_MSG_TRANSACTION_VERSION),
		DP_STR(LINK_ADDRESS),
		DP_STR(CONNECTION_STATUS_NOTIFY),
		DP_STR(ENUM_PATH_RESOURCES),
		DP_STR(ALLOCATE_PAYLOAD),
		DP_STR(QUERY_PAYLOAD),
		DP_STR(RESOURCE_STATUS_NOTIFY),
		DP_STR(CLEAR_PAYLOAD_ID_TABLE),
		DP_STR(REMOTE_DPCD_READ),
		DP_STR(REMOTE_DPCD_WRITE),
		DP_STR(REMOTE_I2C_READ),
		DP_STR(REMOTE_I2C_WRITE),
		DP_STR(POWER_UP_PHY),
		DP_STR(POWER_DOWN_PHY),
		DP_STR(SINK_EVENT_NOTIFY),
		DP_STR(QUERY_STREAM_ENC_STATUS),
	};

	if (req_type >= ARRAY_SIZE(req_type_str) ||
	    !req_type_str[req_type])
		return "unknown";

	return req_type_str[req_type];
}

#undef DP_STR
#define DP_STR(x) [DP_NAK_ ## x] = #x

static const char *drm_dp_mst_nak_reason_str(u8 nak_reason)
{
	static const char * const nak_reason_str[] = {
		DP_STR(WRITE_FAILURE),
		DP_STR(INVALID_READ),
		DP_STR(CRC_FAILURE),
		DP_STR(BAD_PARAM),
		DP_STR(DEFER),
		DP_STR(LINK_FAILURE),
		DP_STR(NO_RESOURCES),
		DP_STR(DPCD_FAIL),
		DP_STR(I2C_NAK),
		DP_STR(ALLOCATE_FAIL),
	};

	if (nak_reason >= ARRAY_SIZE(nak_reason_str) ||
	    !nak_reason_str[nak_reason])
		return "unknown";

	return nak_reason_str[nak_reason];
}

#undef DP_STR
#define DP_STR(x) [DRM_DP_SIDEBAND_TX_ ## x] = #x

static const char *drm_dp_mst_sideband_tx_state_str(int state)
{
	static const char * const sideband_reason_str[] = {
		DP_STR(QUEUED),
		DP_STR(START_SEND),
		DP_STR(SENT),
		DP_STR(RX),
		DP_STR(TIMEOUT),
	};

	if (state >= ARRAY_SIZE(sideband_reason_str) ||
	    !sideband_reason_str[state])
		return "unknown";

	return sideband_reason_str[state];
}

static int
drm_dp_mst_rad_to_str(const u8 rad[8], u8 lct, char *out, size_t len)
{
	int i;
	u8 unpacked_rad[16];

	for (i = 0; i < lct; i++) {
		if (i % 2)
			unpacked_rad[i] = rad[i / 2] >> 4;
		else
			unpacked_rad[i] = rad[i / 2] & BIT_MASK(4);
	}

	/* TODO: Eventually add something to printk so we can format the rad
	 * like this: 1.2.3
	 */
	return snprintf(out, len, "%*phC", lct, unpacked_rad);
}

/* sideband msg handling */
static u8 drm_dp_msg_header_crc4(const uint8_t *data, size_t num_nibbles)
{
	u8 bitmask = 0x80;
	u8 bitshift = 7;
	u8 array_index = 0;
	int number_of_bits = num_nibbles * 4;
	u8 remainder = 0;

	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		remainder |= (data[array_index] & bitmask) >> bitshift;
		bitmask >>= 1;
		bitshift--;
		if (bitmask == 0) {
			bitmask = 0x80;
			bitshift = 7;
			array_index++;
		}
		if ((remainder & 0x10) == 0x10)
			remainder ^= 0x13;
	}

	number_of_bits = 4;
	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		if ((remainder & 0x10) != 0)
			remainder ^= 0x13;
	}

	return remainder;
}

static u8 drm_dp_msg_data_crc4(const uint8_t *data, u8 number_of_bytes)
{
	u8 bitmask = 0x80;
	u8 bitshift = 7;
	u8 array_index = 0;
	int number_of_bits = number_of_bytes * 8;
	u16 remainder = 0;

	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		remainder |= (data[array_index] & bitmask) >> bitshift;
		bitmask >>= 1;
		bitshift--;
		if (bitmask == 0) {
			bitmask = 0x80;
			bitshift = 7;
			array_index++;
		}
		if ((remainder & 0x100) == 0x100)
			remainder ^= 0xd5;
	}

	number_of_bits = 8;
	while (number_of_bits != 0) {
		number_of_bits--;
		remainder <<= 1;
		if ((remainder & 0x100) != 0)
			remainder ^= 0xd5;
	}

	return remainder & 0xff;
}
static inline u8 drm_dp_calc_sb_hdr_size(struct drm_dp_sideband_msg_hdr *hdr)
{
	u8 size = 3;

	size += (hdr->lct / 2);
	return size;
}

static void drm_dp_encode_sideband_msg_hdr(struct drm_dp_sideband_msg_hdr *hdr,
					   u8 *buf, int *len)
{
	int idx = 0;
	int i;
	u8 crc4;

	buf[idx++] = ((hdr->lct & 0xf) << 4) | (hdr->lcr & 0xf);
	for (i = 0; i < (hdr->lct / 2); i++)
		buf[idx++] = hdr->rad[i];
	buf[idx++] = (hdr->broadcast << 7) | (hdr->path_msg << 6) |
		(hdr->msg_len & 0x3f);
	buf[idx++] = (hdr->somt << 7) | (hdr->eomt << 6) | (hdr->seqno << 4);

	crc4 = drm_dp_msg_header_crc4(buf, (idx * 2) - 1);
	buf[idx - 1] |= (crc4 & 0xf);

	*len = idx;
}

static bool drm_dp_decode_sideband_msg_hdr(const struct drm_dp_mst_topology_mgr *mgr,
					   struct drm_dp_sideband_msg_hdr *hdr,
					   u8 *buf, int buflen, u8 *hdrlen)
{
	u8 crc4;
	u8 len;
	int i;
	u8 idx;

	if (buf[0] == 0)
		return false;
	len = 3;
	len += ((buf[0] & 0xf0) >> 4) / 2;
	if (len > buflen)
		return false;
	crc4 = drm_dp_msg_header_crc4(buf, (len * 2) - 1);

	if ((crc4 & 0xf) != (buf[len - 1] & 0xf)) {
		drm_dbg_kms(mgr->dev, "crc4 mismatch 0x%x 0x%x\n", crc4, buf[len - 1]);
		return false;
	}

	hdr->lct = (buf[0] & 0xf0) >> 4;
	hdr->lcr = (buf[0] & 0xf);
	idx = 1;
	for (i = 0; i < (hdr->lct / 2); i++)
		hdr->rad[i] = buf[idx++];
	hdr->broadcast = (buf[idx] >> 7) & 0x1;
	hdr->path_msg = (buf[idx] >> 6) & 0x1;
	hdr->msg_len = buf[idx] & 0x3f;
	idx++;
	hdr->somt = (buf[idx] >> 7) & 0x1;
	hdr->eomt = (buf[idx] >> 6) & 0x1;
	hdr->seqno = (buf[idx] >> 4) & 0x1;
	idx++;
	*hdrlen = idx;
	return true;
}

void
drm_dp_encode_sideband_req(const struct drm_dp_sideband_msg_req_body *req,
			   struct drm_dp_sideband_msg_tx *raw)
{
	int idx = 0;
	int i;
	u8 *buf = raw->msg;

	buf[idx++] = req->req_type & 0x7f;

	switch (req->req_type) {
	case DP_ENUM_PATH_RESOURCES:
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		buf[idx] = (req->u.port_num.port_number & 0xf) << 4;
		idx++;
		break;
	case DP_ALLOCATE_PAYLOAD:
		buf[idx] = (req->u.allocate_payload.port_number & 0xf) << 4 |
			(req->u.allocate_payload.number_sdp_streams & 0xf);
		idx++;
		buf[idx] = (req->u.allocate_payload.vcpi & 0x7f);
		idx++;
		buf[idx] = (req->u.allocate_payload.pbn >> 8);
		idx++;
		buf[idx] = (req->u.allocate_payload.pbn & 0xff);
		idx++;
		for (i = 0; i < req->u.allocate_payload.number_sdp_streams / 2; i++) {
			buf[idx] = ((req->u.allocate_payload.sdp_stream_sink[i * 2] & 0xf) << 4) |
				(req->u.allocate_payload.sdp_stream_sink[i * 2 + 1] & 0xf);
			idx++;
		}
		if (req->u.allocate_payload.number_sdp_streams & 1) {
			i = req->u.allocate_payload.number_sdp_streams - 1;
			buf[idx] = (req->u.allocate_payload.sdp_stream_sink[i] & 0xf) << 4;
			idx++;
		}
		break;
	case DP_QUERY_PAYLOAD:
		buf[idx] = (req->u.query_payload.port_number & 0xf) << 4;
		idx++;
		buf[idx] = (req->u.query_payload.vcpi & 0x7f);
		idx++;
		break;
	case DP_REMOTE_DPCD_READ:
		buf[idx] = (req->u.dpcd_read.port_number & 0xf) << 4;
		buf[idx] |= ((req->u.dpcd_read.dpcd_address & 0xf0000) >> 16) & 0xf;
		idx++;
		buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff00) >> 8;
		idx++;
		buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff);
		idx++;
		buf[idx] = (req->u.dpcd_read.num_bytes);
		idx++;
		break;

	case DP_REMOTE_DPCD_WRITE:
		buf[idx] = (req->u.dpcd_write.port_number & 0xf) << 4;
		buf[idx] |= ((req->u.dpcd_write.dpcd_address & 0xf0000) >> 16) & 0xf;
		idx++;
		buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff00) >> 8;
		idx++;
		buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff);
		idx++;
		buf[idx] = (req->u.dpcd_write.num_bytes);
		idx++;
		memcpy(&buf[idx], req->u.dpcd_write.bytes, req->u.dpcd_write.num_bytes);
		idx += req->u.dpcd_write.num_bytes;
		break;
	case DP_REMOTE_I2C_READ:
		buf[idx] = (req->u.i2c_read.port_number & 0xf) << 4;
		buf[idx] |= (req->u.i2c_read.num_transactions & 0x3);
		idx++;
		for (i = 0; i < (req->u.i2c_read.num_transactions & 0x3); i++) {
			buf[idx] = req->u.i2c_read.transactions[i].i2c_dev_id & 0x7f;
			idx++;
			buf[idx] = req->u.i2c_read.transactions[i].num_bytes;
			idx++;
			memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes);
			idx += req->u.i2c_read.transactions[i].num_bytes;

			buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4;
			buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf);
			idx++;
		}
		buf[idx] = (req->u.i2c_read.read_i2c_device_id) & 0x7f;
		idx++;
		buf[idx] = (req->u.i2c_read.num_bytes_read);
		idx++;
		break;

	case DP_REMOTE_I2C_WRITE:
		buf[idx] = (req->u.i2c_write.port_number & 0xf) << 4;
		idx++;
		buf[idx] = (req->u.i2c_write.write_i2c_device_id) & 0x7f;
		idx++;
		buf[idx] = (req->u.i2c_write.num_bytes);
		idx++;
		memcpy(&buf[idx], req->u.i2c_write.bytes, req->u.i2c_write.num_bytes);
		idx += req->u.i2c_write.num_bytes;
		break;
	case DP_QUERY_STREAM_ENC_STATUS: {
		const struct drm_dp_query_stream_enc_status *msg;

		msg = &req->u.enc_status;
		buf[idx] = msg->stream_id;
		idx++;
		memcpy(&buf[idx], msg->client_id, sizeof(msg->client_id));
		idx += sizeof(msg->client_id);
		buf[idx] = 0;
		buf[idx] |= FIELD_PREP(GENMASK(1, 0), msg->stream_event);
		buf[idx] |= msg->valid_stream_event ? BIT(2) : 0;
		buf[idx] |= FIELD_PREP(GENMASK(4, 3), msg->stream_behavior);
		buf[idx] |= msg->valid_stream_behavior ? BIT(5) : 0;
		idx++;
		}
		break;
	}
	raw->cur_len = idx;
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_encode_sideband_req);

/* Decode a sideband request we've encoded, mainly used for debugging */
int
drm_dp_decode_sideband_req(const struct drm_dp_sideband_msg_tx *raw,
			   struct drm_dp_sideband_msg_req_body *req)
{
	const u8 *buf = raw->msg;
	int i, idx = 0;

	req->req_type = buf[idx++] & 0x7f;
	switch (req->req_type) {
	case DP_ENUM_PATH_RESOURCES:
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		req->u.port_num.port_number = (buf[idx] >> 4) & 0xf;
		break;
	case DP_ALLOCATE_PAYLOAD:
		{
			struct drm_dp_allocate_payload *a =
				&req->u.allocate_payload;

			a->number_sdp_streams = buf[idx] & 0xf;
			a->port_number = (buf[idx] >> 4) & 0xf;

			WARN_ON(buf[++idx] & 0x80);
			a->vcpi = buf[idx] & 0x7f;

			a->pbn = buf[++idx] << 8;
			a->pbn |= buf[++idx];

			idx++;
			for (i = 0; i < a->number_sdp_streams; i++) {
				a->sdp_stream_sink[i] =
					(buf[idx + (i / 2)] >> ((i % 2) ? 0 : 4)) & 0xf;
			}
		}
		break;
	case DP_QUERY_PAYLOAD:
		req->u.query_payload.port_number = (buf[idx] >> 4) & 0xf;
		WARN_ON(buf[++idx] & 0x80);
		req->u.query_payload.vcpi = buf[idx] & 0x7f;
		break;
	case DP_REMOTE_DPCD_READ:
		{
			struct drm_dp_remote_dpcd_read *r = &req->u.dpcd_read;

			r->port_number = (buf[idx] >> 4) & 0xf;

			r->dpcd_address = (buf[idx] << 16) & 0xf0000;
			r->dpcd_address |= (buf[++idx] << 8) & 0xff00;
			r->dpcd_address |= buf[++idx] & 0xff;

			r->num_bytes = buf[++idx];
		}
		break;
	case DP_REMOTE_DPCD_WRITE:
		{
			struct drm_dp_remote_dpcd_write *w =
				&req->u.dpcd_write;

			w->port_number = (buf[idx] >> 4) & 0xf;

			w->dpcd_address = (buf[idx] << 16) & 0xf0000;
			w->dpcd_address |= (buf[++idx] << 8) & 0xff00;
			w->dpcd_address |= buf[++idx] & 0xff;

			w->num_bytes = buf[++idx];

			w->bytes = kmemdup(&buf[++idx], w->num_bytes,
					   GFP_KERNEL);
			if (!w->bytes)
				return -ENOMEM;
		}
		break;
	case DP_REMOTE_I2C_READ:
		{
			struct drm_dp_remote_i2c_read *r = &req->u.i2c_read;
			struct drm_dp_remote_i2c_read_tx *tx;
			bool failed = false;

			r->num_transactions = buf[idx] & 0x3;
			r->port_number = (buf[idx] >> 4) & 0xf;
			for (i = 0; i < r->num_transactions; i++) {
				tx = &r->transactions[i];

				tx->i2c_dev_id = buf[++idx] & 0x7f;
				tx->num_bytes = buf[++idx];
				tx->bytes = kmemdup(&buf[++idx],
						    tx->num_bytes,
						    GFP_KERNEL);
				if (!tx->bytes) {
					failed = true;
					break;
				}
				idx += tx->num_bytes;
				tx->no_stop_bit = (buf[idx] >> 5) & 0x1;
				tx->i2c_transaction_delay = buf[idx] & 0xf;
			}

			if (failed) {
				for (i = 0; i < r->num_transactions; i++) {
					tx = &r->transactions[i];
					kfree(tx->bytes);
				}
				return -ENOMEM;
			}

			r->read_i2c_device_id = buf[++idx] & 0x7f;
			r->num_bytes_read = buf[++idx];
		}
		break;
	case DP_REMOTE_I2C_WRITE:
		{
			struct drm_dp_remote_i2c_write *w = &req->u.i2c_write;

			w->port_number = (buf[idx] >> 4) & 0xf;
			w->write_i2c_device_id = buf[++idx] & 0x7f;
			w->num_bytes = buf[++idx];
			w->bytes = kmemdup(&buf[++idx], w->num_bytes,
					   GFP_KERNEL);
			if (!w->bytes)
				return -ENOMEM;
		}
		break;
	case DP_QUERY_STREAM_ENC_STATUS:
		req->u.enc_status.stream_id = buf[idx++];
		for (i = 0; i < sizeof(req->u.enc_status.client_id); i++)
			req->u.enc_status.client_id[i] = buf[idx++];

		req->u.enc_status.stream_event = FIELD_GET(GENMASK(1, 0),
							   buf[idx]);
		req->u.enc_status.valid_stream_event = FIELD_GET(BIT(2),
								 buf[idx]);
		req->u.enc_status.stream_behavior = FIELD_GET(GENMASK(4, 3),
							      buf[idx]);
		req->u.enc_status.valid_stream_behavior = FIELD_GET(BIT(5),
								    buf[idx]);
		break;
	}

	return 0;
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_decode_sideband_req);

void
drm_dp_dump_sideband_msg_req_body(const struct drm_dp_sideband_msg_req_body *req,
				  int indent, struct drm_printer *printer)
{
	int i;

#define P(f, ...) drm_printf_indent(printer, indent, f, ##__VA_ARGS__)
	if (req->req_type == DP_LINK_ADDRESS) {
		/* No contents to print */
		P("type=%s\n", drm_dp_mst_req_type_str(req->req_type));
		return;
	}

	P("type=%s contents:\n", drm_dp_mst_req_type_str(req->req_type));
	indent++;

	switch (req->req_type) {
	case DP_ENUM_PATH_RESOURCES:
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		P("port=%d\n", req->u.port_num.port_number);
		break;
	case DP_ALLOCATE_PAYLOAD:
		P("port=%d vcpi=%d pbn=%d sdp_streams=%d %*ph\n",
		  req->u.allocate_payload.port_number,
		  req->u.allocate_payload.vcpi, req->u.allocate_payload.pbn,
		  req->u.allocate_payload.number_sdp_streams,
		  req->u.allocate_payload.number_sdp_streams,
		  req->u.allocate_payload.sdp_stream_sink);
		break;
	case DP_QUERY_PAYLOAD:
		P("port=%d vcpi=%d\n",
		  req->u.query_payload.port_number,
		  req->u.query_payload.vcpi);
		break;
	case DP_REMOTE_DPCD_READ:
		P("port=%d dpcd_addr=%05x len=%d\n",
		  req->u.dpcd_read.port_number, req->u.dpcd_read.dpcd_address,
		  req->u.dpcd_read.num_bytes);
		break;
	case DP_REMOTE_DPCD_WRITE:
		P("port=%d addr=%05x len=%d: %*ph\n",
		  req->u.dpcd_write.port_number,
		  req->u.dpcd_write.dpcd_address,
		  req->u.dpcd_write.num_bytes, req->u.dpcd_write.num_bytes,
		  req->u.dpcd_write.bytes);
		break;
	case DP_REMOTE_I2C_READ:
		P("port=%d num_tx=%d id=%d size=%d:\n",
		  req->u.i2c_read.port_number,
		  req->u.i2c_read.num_transactions,
		  req->u.i2c_read.read_i2c_device_id,
		  req->u.i2c_read.num_bytes_read);

		indent++;
		for (i = 0; i < req->u.i2c_read.num_transactions; i++) {
			const struct drm_dp_remote_i2c_read_tx *rtx =
				&req->u.i2c_read.transactions[i];

			P("%d: id=%03d size=%03d no_stop_bit=%d tx_delay=%03d: %*ph\n",
			  i, rtx->i2c_dev_id, rtx->num_bytes,
			  rtx->no_stop_bit, rtx->i2c_transaction_delay,
			  rtx->num_bytes, rtx->bytes);
		}
		break;
	case DP_REMOTE_I2C_WRITE:
		P("port=%d id=%d size=%d: %*ph\n",
		  req->u.i2c_write.port_number,
		  req->u.i2c_write.write_i2c_device_id,
		  req->u.i2c_write.num_bytes, req->u.i2c_write.num_bytes,
		  req->u.i2c_write.bytes);
		break;
	case DP_QUERY_STREAM_ENC_STATUS:
		P("stream_id=%u client_id=%*ph stream_event=%x "
		  "valid_event=%d stream_behavior=%x valid_behavior=%d",
		  req->u.enc_status.stream_id,
		  (int)ARRAY_SIZE(req->u.enc_status.client_id),
		  req->u.enc_status.client_id, req->u.enc_status.stream_event,
		  req->u.enc_status.valid_stream_event,
		  req->u.enc_status.stream_behavior,
		  req->u.enc_status.valid_stream_behavior);
		break;
	default:
		P("???\n");
		break;
	}
#undef P
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_dump_sideband_msg_req_body);

static inline void
drm_dp_mst_dump_sideband_msg_tx(struct drm_printer *p,
				const struct drm_dp_sideband_msg_tx *txmsg)
{
	struct drm_dp_sideband_msg_req_body req;
	char buf[64];
	int ret;
	int i;

	drm_dp_mst_rad_to_str(txmsg->dst->rad, txmsg->dst->lct, buf,
			      sizeof(buf));
	drm_printf(p, "txmsg cur_offset=%x cur_len=%x seqno=%x state=%s path_msg=%d dst=%s\n",
		   txmsg->cur_offset, txmsg->cur_len, txmsg->seqno,
		   drm_dp_mst_sideband_tx_state_str(txmsg->state),
		   txmsg->path_msg, buf);

	ret = drm_dp_decode_sideband_req(txmsg, &req);
	if (ret) {
		drm_printf(p, "<failed to decode sideband req: %d>\n", ret);
		return;
	}
	drm_dp_dump_sideband_msg_req_body(&req, 1, p);

	switch (req.req_type) {
	case DP_REMOTE_DPCD_WRITE:
		kfree(req.u.dpcd_write.bytes);
		break;
	case DP_REMOTE_I2C_READ:
		for (i = 0; i < req.u.i2c_read.num_transactions; i++)
			kfree(req.u.i2c_read.transactions[i].bytes);
		break;
	case DP_REMOTE_I2C_WRITE:
		kfree(req.u.i2c_write.bytes);
		break;
	}
}

static void drm_dp_crc_sideband_chunk_req(u8 *msg, u8 len)
{
	u8 crc4;

	crc4 = drm_dp_msg_data_crc4(msg, len);
	msg[len] = crc4;
}

static void drm_dp_encode_sideband_reply(struct drm_dp_sideband_msg_reply_body *rep,
					 struct drm_dp_sideband_msg_tx *raw)
{
	int idx = 0;
	u8 *buf = raw->msg;

	buf[idx++] = (rep->reply_type & 0x1) << 7 | (rep->req_type & 0x7f);

	raw->cur_len = idx;
}

static int drm_dp_sideband_msg_set_header(struct drm_dp_sideband_msg_rx *msg,
					  struct drm_dp_sideband_msg_hdr *hdr,
					  u8 hdrlen)
{
	/*
	 * ignore out-of-order messages or messages that are part of a
	 * failed transaction
	 */
	if (!hdr->somt && !msg->have_somt)
		return false;

	/* get length contained in this portion */
	msg->curchunk_idx = 0;
	msg->curchunk_len = hdr->msg_len;
	msg->curchunk_hdrlen = hdrlen;

	/* we have already gotten an somt - don't bother parsing */
	if (hdr->somt && msg->have_somt)
		return false;

	if (hdr->somt) {
		memcpy(&msg->initial_hdr, hdr,
		       sizeof(struct drm_dp_sideband_msg_hdr));
		msg->have_somt = true;
	}
	if (hdr->eomt)
		msg->have_eomt = true;

	return true;
}

/* this adds a chunk of msg to the builder to get the final msg */
static bool drm_dp_sideband_append_payload(struct drm_dp_sideband_msg_rx *msg,
					   u8 *replybuf, u8 replybuflen)
{
	u8 crc4;

	memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen);
	msg->curchunk_idx += replybuflen;

	if (msg->curchunk_idx >= msg->curchunk_len) {
		/* do CRC */
		crc4 = drm_dp_msg_data_crc4(msg->chunk, msg->curchunk_len - 1);
		if (crc4 != msg->chunk[msg->curchunk_len - 1])
			print_hex_dump(KERN_DEBUG, "wrong crc",
				       DUMP_PREFIX_NONE, 16, 1,
				       msg->chunk,  msg->curchunk_len, false);
		/* copy chunk into bigger msg */
		memcpy(&msg->msg[msg->curlen], msg->chunk, msg->curchunk_len - 1);
		msg->curlen += msg->curchunk_len - 1;
	}
	return true;
}

static bool drm_dp_sideband_parse_link_address(const struct drm_dp_mst_topology_mgr *mgr,
					       struct drm_dp_sideband_msg_rx *raw,
					       struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;
	int i;

	memcpy(repmsg->u.link_addr.guid, &raw->msg[idx], 16);
	idx += 16;
	repmsg->u.link_addr.nports = raw->msg[idx] & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	for (i = 0; i < repmsg->u.link_addr.nports; i++) {
		if (raw->msg[idx] & 0x80)
			repmsg->u.link_addr.ports[i].input_port = 1;

		repmsg->u.link_addr.ports[i].peer_device_type = (raw->msg[idx] >> 4) & 0x7;
		repmsg->u.link_addr.ports[i].port_number = (raw->msg[idx] & 0xf);

		idx++;
		if (idx > raw->curlen)
			goto fail_len;
		repmsg->u.link_addr.ports[i].mcs = (raw->msg[idx] >> 7) & 0x1;
		repmsg->u.link_addr.ports[i].ddps = (raw->msg[idx] >> 6) & 0x1;
		if (repmsg->u.link_addr.ports[i].input_port == 0)
			repmsg->u.link_addr.ports[i].legacy_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
		idx++;
		if (idx > raw->curlen)
			goto fail_len;
		if (repmsg->u.link_addr.ports[i].input_port == 0) {
			repmsg->u.link_addr.ports[i].dpcd_revision = (raw->msg[idx]);
			idx++;
			if (idx > raw->curlen)
				goto fail_len;
			memcpy(repmsg->u.link_addr.ports[i].peer_guid, &raw->msg[idx], 16);
			idx += 16;
			if (idx > raw->curlen)
				goto fail_len;
			repmsg->u.link_addr.ports[i].num_sdp_streams = (raw->msg[idx] >> 4) & 0xf;
			repmsg->u.link_addr.ports[i].num_sdp_stream_sinks = (raw->msg[idx] & 0xf);
			idx++;

		}
		if (idx > raw->curlen)
			goto fail_len;
	}

	return true;
fail_len:
	DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_remote_dpcd_read(struct drm_dp_sideband_msg_rx *raw,
						   struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.remote_dpcd_read_ack.port_number = raw->msg[idx] & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.remote_dpcd_read_ack.num_bytes = raw->msg[idx];
	idx++;
	if (idx > raw->curlen)
		goto fail_len;

	memcpy(repmsg->u.remote_dpcd_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_dpcd_read_ack.num_bytes);
	return true;
fail_len:
	DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_remote_dpcd_write(struct drm_dp_sideband_msg_rx *raw,
						      struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.remote_dpcd_write_ack.port_number = raw->msg[idx] & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_remote_i2c_read_ack(struct drm_dp_sideband_msg_rx *raw,
						      struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.remote_i2c_read_ack.port_number = (raw->msg[idx] & 0xf);
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.remote_i2c_read_ack.num_bytes = raw->msg[idx];
	idx++;
	/* TODO check */
	memcpy(repmsg->u.remote_i2c_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_i2c_read_ack.num_bytes);
	return true;
fail_len:
	DRM_DEBUG_KMS("remote i2c reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_enum_path_resources_ack(struct drm_dp_sideband_msg_rx *raw,
							  struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.path_resources.port_number = (raw->msg[idx] >> 4) & 0xf;
	repmsg->u.path_resources.fec_capable = raw->msg[idx] & 0x1;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.path_resources.full_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.path_resources.avail_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("enum resource parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_allocate_payload_ack(struct drm_dp_sideband_msg_rx *raw,
							  struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.allocate_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.allocate_payload.vcpi = raw->msg[idx];
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.allocate_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("allocate payload parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_query_payload_ack(struct drm_dp_sideband_msg_rx *raw,
						    struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.query_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;
	repmsg->u.query_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
	idx += 2;
	if (idx > raw->curlen)
		goto fail_len;
	return true;
fail_len:
	DRM_DEBUG_KMS("query payload parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_power_updown_phy_ack(struct drm_dp_sideband_msg_rx *raw,
						       struct drm_dp_sideband_msg_reply_body *repmsg)
{
	int idx = 1;

	repmsg->u.port_number.port_number = (raw->msg[idx] >> 4) & 0xf;
	idx++;
	if (idx > raw->curlen) {
		DRM_DEBUG_KMS("power up/down phy parse length fail %d %d\n",
			      idx, raw->curlen);
		return false;
	}
	return true;
}

static bool
drm_dp_sideband_parse_query_stream_enc_status(
				struct drm_dp_sideband_msg_rx *raw,
				struct drm_dp_sideband_msg_reply_body *repmsg)
{
	struct drm_dp_query_stream_enc_status_ack_reply *reply;

	reply = &repmsg->u.enc_status;

	reply->stream_id = raw->msg[3];

	reply->reply_signed = raw->msg[2] & BIT(0);

	/*
	 * NOTE: It's my impression from reading the spec that the below parsing
	 * is correct. However I noticed while testing with an HDCP 1.4 display
	 * through an HDCP 2.2 hub that only bit 3 was set. In that case, I
	 * would expect both bits to be set. So keep the parsing following the
	 * spec, but beware reality might not match the spec (at least for some
	 * configurations).
	 */
	reply->hdcp_1x_device_present = raw->msg[2] & BIT(4);
	reply->hdcp_2x_device_present = raw->msg[2] & BIT(3);

	reply->query_capable_device_present = raw->msg[2] & BIT(5);
	reply->legacy_device_present = raw->msg[2] & BIT(6);
	reply->unauthorizable_device_present = raw->msg[2] & BIT(7);

	reply->auth_completed = !!(raw->msg[1] & BIT(3));
	reply->encryption_enabled = !!(raw->msg[1] & BIT(4));
	reply->repeater_present = !!(raw->msg[1] & BIT(5));
	reply->state = (raw->msg[1] & GENMASK(7, 6)) >> 6;

	return true;
}

static bool drm_dp_sideband_parse_reply(const struct drm_dp_mst_topology_mgr *mgr,
					struct drm_dp_sideband_msg_rx *raw,
					struct drm_dp_sideband_msg_reply_body *msg)
{
	memset(msg, 0, sizeof(*msg));
	msg->reply_type = (raw->msg[0] & 0x80) >> 7;
	msg->req_type = (raw->msg[0] & 0x7f);

	if (msg->reply_type == DP_SIDEBAND_REPLY_NAK) {
		memcpy(msg->u.nak.guid, &raw->msg[1], 16);
		msg->u.nak.reason = raw->msg[17];
		msg->u.nak.nak_data = raw->msg[18];
		return false;
	}

	switch (msg->req_type) {
	case DP_LINK_ADDRESS:
		return drm_dp_sideband_parse_link_address(mgr, raw, msg);
	case DP_QUERY_PAYLOAD:
		return drm_dp_sideband_parse_query_payload_ack(raw, msg);
	case DP_REMOTE_DPCD_READ:
		return drm_dp_sideband_parse_remote_dpcd_read(raw, msg);
	case DP_REMOTE_DPCD_WRITE:
		return drm_dp_sideband_parse_remote_dpcd_write(raw, msg);
	case DP_REMOTE_I2C_READ:
		return drm_dp_sideband_parse_remote_i2c_read_ack(raw, msg);
	case DP_REMOTE_I2C_WRITE:
		return true; /* since there's nothing to parse */
	case DP_ENUM_PATH_RESOURCES:
		return drm_dp_sideband_parse_enum_path_resources_ack(raw, msg);
	case DP_ALLOCATE_PAYLOAD:
		return drm_dp_sideband_parse_allocate_payload_ack(raw, msg);
	case DP_POWER_DOWN_PHY:
	case DP_POWER_UP_PHY:
		return drm_dp_sideband_parse_power_updown_phy_ack(raw, msg);
	case DP_CLEAR_PAYLOAD_ID_TABLE:
		return true; /* since there's nothing to parse */
	case DP_QUERY_STREAM_ENC_STATUS:
		return drm_dp_sideband_parse_query_stream_enc_status(raw, msg);
	default:
		drm_err(mgr->dev, "Got unknown reply 0x%02x (%s)\n",
			msg->req_type, drm_dp_mst_req_type_str(msg->req_type));
		return false;
	}
}

static bool
drm_dp_sideband_parse_connection_status_notify(const struct drm_dp_mst_topology_mgr *mgr,
					       struct drm_dp_sideband_msg_rx *raw,
					       struct drm_dp_sideband_msg_req_body *msg)
{
	int idx = 1;

	msg->u.conn_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;

	memcpy(msg->u.conn_stat.guid, &raw->msg[idx], 16);
	idx += 16;
	if (idx > raw->curlen)
		goto fail_len;

	msg->u.conn_stat.legacy_device_plug_status = (raw->msg[idx] >> 6) & 0x1;
	msg->u.conn_stat.displayport_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
	msg->u.conn_stat.message_capability_status = (raw->msg[idx] >> 4) & 0x1;
	msg->u.conn_stat.input_port = (raw->msg[idx] >> 3) & 0x1;
	msg->u.conn_stat.peer_device_type = (raw->msg[idx] & 0x7);
	idx++;
	return true;
fail_len:
	drm_dbg_kms(mgr->dev, "connection status reply parse length fail %d %d\n",
		    idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_resource_status_notify(const struct drm_dp_mst_topology_mgr *mgr,
							 struct drm_dp_sideband_msg_rx *raw,
							 struct drm_dp_sideband_msg_req_body *msg)
{
	int idx = 1;

	msg->u.resource_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
	idx++;
	if (idx > raw->curlen)
		goto fail_len;

	memcpy(msg->u.resource_stat.guid, &raw->msg[idx], 16);
	idx += 16;
	if (idx > raw->curlen)
		goto fail_len;

	msg->u.resource_stat.available_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
	idx++;
	return true;
fail_len:
	drm_dbg_kms(mgr->dev, "resource status reply parse length fail %d %d\n", idx, raw->curlen);
	return false;
}

static bool drm_dp_sideband_parse_req(const struct drm_dp_mst_topology_mgr *mgr,
				      struct drm_dp_sideband_msg_rx *raw,
				      struct drm_dp_sideband_msg_req_body *msg)
{
	memset(msg, 0, sizeof(*msg));
	msg->req_type = (raw->msg[0] & 0x7f);

	switch (msg->req_type) {
	case DP_CONNECTION_STATUS_NOTIFY:
		return drm_dp_sideband_parse_connection_status_notify(mgr, raw, msg);
	case DP_RESOURCE_STATUS_NOTIFY:
		return drm_dp_sideband_parse_resource_status_notify(mgr, raw, msg);
	default:
		drm_err(mgr->dev, "Got unknown request 0x%02x (%s)\n",
			msg->req_type, drm_dp_mst_req_type_str(msg->req_type));
		return false;
	}
}

static void build_dpcd_write(struct drm_dp_sideband_msg_tx *msg,
			     u8 port_num, u32 offset, u8 num_bytes, u8 *bytes)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_REMOTE_DPCD_WRITE;
	req.u.dpcd_write.port_number = port_num;
	req.u.dpcd_write.dpcd_address = offset;
	req.u.dpcd_write.num_bytes = num_bytes;
	req.u.dpcd_write.bytes = bytes;
	drm_dp_encode_sideband_req(&req, msg);
}

static void build_link_address(struct drm_dp_sideband_msg_tx *msg)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_LINK_ADDRESS;
	drm_dp_encode_sideband_req(&req, msg);
}

static void build_clear_payload_id_table(struct drm_dp_sideband_msg_tx *msg)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_CLEAR_PAYLOAD_ID_TABLE;
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
}

static int build_enum_path_resources(struct drm_dp_sideband_msg_tx *msg,
				     int port_num)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_ENUM_PATH_RESOURCES;
	req.u.port_num.port_number = port_num;
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
	return 0;
}

static void build_allocate_payload(struct drm_dp_sideband_msg_tx *msg,
				   int port_num,
				   u8 vcpi, uint16_t pbn,
				   u8 number_sdp_streams,
				   u8 *sdp_stream_sink)
{
	struct drm_dp_sideband_msg_req_body req;

	memset(&req, 0, sizeof(req));
	req.req_type = DP_ALLOCATE_PAYLOAD;
	req.u.allocate_payload.port_number = port_num;
	req.u.allocate_payload.vcpi = vcpi;
	req.u.allocate_payload.pbn = pbn;
	req.u.allocate_payload.number_sdp_streams = number_sdp_streams;
	memcpy(req.u.allocate_payload.sdp_stream_sink, sdp_stream_sink,
		   number_sdp_streams);
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
}

static void build_power_updown_phy(struct drm_dp_sideband_msg_tx *msg,
				   int port_num, bool power_up)
{
	struct drm_dp_sideband_msg_req_body req;

	if (power_up)
		req.req_type = DP_POWER_UP_PHY;
	else
		req.req_type = DP_POWER_DOWN_PHY;

	req.u.port_num.port_number = port_num;
	drm_dp_encode_sideband_req(&req, msg);
	msg->path_msg = true;
}

static int
build_query_stream_enc_status(struct drm_dp_sideband_msg_tx *msg, u8 stream_id,
			      u8 *q_id)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_QUERY_STREAM_ENC_STATUS;
	req.u.enc_status.stream_id = stream_id;
	memcpy(req.u.enc_status.client_id, q_id,
	       sizeof(req.u.enc_status.client_id));
	req.u.enc_status.stream_event = 0;
	req.u.enc_status.valid_stream_event = false;
	req.u.enc_status.stream_behavior = 0;
	req.u.enc_status.valid_stream_behavior = false;

	drm_dp_encode_sideband_req(&req, msg);
	return 0;
}

static int drm_dp_mst_assign_payload_id(struct drm_dp_mst_topology_mgr *mgr,
					struct drm_dp_vcpi *vcpi)
{
	int ret, vcpi_ret;

	mutex_lock(&mgr->payload_lock);
	ret = find_first_zero_bit(&mgr->payload_mask, mgr->max_payloads + 1);
	if (ret > mgr->max_payloads) {
		ret = -EINVAL;
		drm_dbg_kms(mgr->dev, "out of payload ids %d\n", ret);
		goto out_unlock;
	}

	vcpi_ret = find_first_zero_bit(&mgr->vcpi_mask, mgr->max_payloads + 1);
	if (vcpi_ret > mgr->max_payloads) {
		ret = -EINVAL;
		drm_dbg_kms(mgr->dev, "out of vcpi ids %d\n", ret);
		goto out_unlock;
	}

	set_bit(ret, &mgr->payload_mask);
	set_bit(vcpi_ret, &mgr->vcpi_mask);
	vcpi->vcpi = vcpi_ret + 1;
	mgr->proposed_vcpis[ret - 1] = vcpi;
out_unlock:
	mutex_unlock(&mgr->payload_lock);
	return ret;
}

static void drm_dp_mst_put_payload_id(struct drm_dp_mst_topology_mgr *mgr,
				      int vcpi)
{
	int i;

	if (vcpi == 0)
		return;

	mutex_lock(&mgr->payload_lock);
	drm_dbg_kms(mgr->dev, "putting payload %d\n", vcpi);
	clear_bit(vcpi - 1, &mgr->vcpi_mask);

	for (i = 0; i < mgr->max_payloads; i++) {
		if (mgr->proposed_vcpis[i] &&
		    mgr->proposed_vcpis[i]->vcpi == vcpi) {
			mgr->proposed_vcpis[i] = NULL;
			clear_bit(i + 1, &mgr->payload_mask);
		}
	}
	mutex_unlock(&mgr->payload_lock);
}

static bool check_txmsg_state(struct drm_dp_mst_topology_mgr *mgr,
			      struct drm_dp_sideband_msg_tx *txmsg)
{
	unsigned int state;

	/*
	 * All updates to txmsg->state are protected by mgr->qlock, and the two
	 * cases we check here are terminal states. For those the barriers
	 * provided by the wake_up/wait_event pair are enough.
	 */
	state = READ_ONCE(txmsg->state);
	return (state == DRM_DP_SIDEBAND_TX_RX ||
		state == DRM_DP_SIDEBAND_TX_TIMEOUT);
}

static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
				    struct drm_dp_sideband_msg_tx *txmsg)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	unsigned long wait_timeout = msecs_to_jiffies(4000);
	unsigned long wait_expires = jiffies + wait_timeout;
	int ret;

	for (;;) {
		/*
		 * If the driver provides a way for this, change to
		 * poll-waiting for the MST reply interrupt if we didn't receive
		 * it for 50 msec. This would cater for cases where the HPD
		 * pulse signal got lost somewhere, even though the sink raised
		 * the corresponding MST interrupt correctly. One example is the
		 * Club 3D CAC-1557 TypeC -> DP adapter which for some reason
		 * filters out short pulses with a duration less than ~540 usec.
		 *
		 * The poll period is 50 msec to avoid missing an interrupt
		 * after the sink has cleared it (after a 110msec timeout
		 * since it raised the interrupt).
		 */
		ret = wait_event_timeout(mgr->tx_waitq,
					 check_txmsg_state(mgr, txmsg),
					 mgr->cbs->poll_hpd_irq ?
						msecs_to_jiffies(50) :
						wait_timeout);

		if (ret || !mgr->cbs->poll_hpd_irq ||
		    time_after(jiffies, wait_expires))
			break;

		mgr->cbs->poll_hpd_irq(mgr);
	}

	mutex_lock(&mgr->qlock);
	if (ret > 0) {
		if (txmsg->state == DRM_DP_SIDEBAND_TX_TIMEOUT) {
			ret = -EIO;
			goto out;
		}
	} else {
		drm_dbg_kms(mgr->dev, "timedout msg send %p %d %d\n",
			    txmsg, txmsg->state, txmsg->seqno);

		/* dump some state */
		ret = -EIO;

		/* remove from q */
		if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED ||
		    txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
		    txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
			list_del(&txmsg->next);
	}
out:
	if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
		struct drm_printer p = drm_debug_printer(DBG_PREFIX);

		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
	}
	mutex_unlock(&mgr->qlock);

	drm_dp_mst_kick_tx(mgr);
	return ret;
}

static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
{
	struct drm_dp_mst_branch *mstb;

	mstb = kzalloc(sizeof(*mstb), GFP_KERNEL);
	if (!mstb)
		return NULL;

	mstb->lct = lct;
	if (lct > 1)
		memcpy(mstb->rad, rad, lct / 2);
	INIT_LIST_HEAD(&mstb->ports);
	kref_init(&mstb->topology_kref);
	kref_init(&mstb->malloc_kref);
	return mstb;
}

static void drm_dp_free_mst_branch_device(struct kref *kref)
{
	struct drm_dp_mst_branch *mstb =
		container_of(kref, struct drm_dp_mst_branch, malloc_kref);

	if (mstb->port_parent)
		drm_dp_mst_put_port_malloc(mstb->port_parent);

	kfree(mstb);
}

/**
 * DOC: Branch device and port refcounting
 *
 * Topology refcount overview
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * The refcounting schemes for &struct drm_dp_mst_branch and &struct
 * drm_dp_mst_port are somewhat unusual. Both ports and branch devices have
 * two different kinds of refcounts: topology refcounts, and malloc refcounts.
 *
 * Topology refcounts are not exposed to drivers, and are handled internally
 * by the DP MST helpers. The helpers use them in order to prevent the
 * in-memory topology state from being changed in the middle of critical
 * operations like changing the internal state of payload allocations. This
 * means each branch and port will be considered to be connected to the rest
 * of the topology until its topology refcount reaches zero. Additionally,
 * for ports this means that their associated &struct drm_connector will stay
 * registered with userspace until the port's refcount reaches 0.
 *
 * Malloc refcount overview
 * ~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * Malloc references are used to keep a &struct drm_dp_mst_port or &struct
 * drm_dp_mst_branch allocated even after all of its topology references have
 * been dropped, so that the driver or MST helpers can safely access each
 * branch's last known state before it was disconnected from the topology.
 * When the malloc refcount of a port or branch reaches 0, the memory
 * allocation containing the &struct drm_dp_mst_branch or &struct
 * drm_dp_mst_port respectively will be freed.
 *
 * For &struct drm_dp_mst_branch, malloc refcounts are not currently exposed
 * to drivers. As of writing this documentation, there are no drivers that
 * have a usecase for accessing &struct drm_dp_mst_branch outside of the MST
 * helpers. Exposing this API to drivers in a race-free manner would take more
 * tweaking of the refcounting scheme, however patches are welcome provided
 * there is a legitimate driver usecase for this.
 *
 * Refcount relationships in a topology
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * Let's take a look at why the relationship between topology and malloc
 * refcounts is designed the way it is.
 *
 * .. kernel-figure:: dp-mst/topology-figure-1.dot
 *
 *    An example of topology and malloc refs in a DP MST topology with two
 *    active payloads. Topology refcount increments are indicated by solid
 *    lines, and malloc refcount increments are indicated by dashed lines.
 *    Each starts from the branch which incremented the refcount, and ends at
 *    the branch to which the refcount belongs to, i.e. the arrow points the
 *    same way as the C pointers used to reference a structure.
 *
 * As you can see in the above figure, every branch increments the topology
 * refcount of its children, and increments the malloc refcount of its
 * parent. Additionally, every payload increments the malloc refcount of its
 * assigned port by 1.
 *
 * So, what would happen if MSTB #3 from the above figure was unplugged from
 * the system, but the driver hadn't yet removed payload #2 from port #3? The
 * topology would start to look like the figure below.
 *
 * .. kernel-figure:: dp-mst/topology-figure-2.dot
 *
 *    Ports and branch devices which have been released from memory are
 *    colored grey, and references which have been removed are colored red.
 *
 * Whenever a port or branch device's topology refcount reaches zero, it will
 * decrement the topology refcounts of all its children, the malloc refcount
 * of its parent, and finally its own malloc refcount. For MSTB #4 and port
 * #4, this means they both have been disconnected from the topology and freed
 * from memory. But, because payload #2 is still holding a reference to port
 * #3, port #3 is removed from the topology but its &struct drm_dp_mst_port
 * is still accessible from memory. This also means port #3 has not yet
 * decremented the malloc refcount of MSTB #3, so its &struct
 * drm_dp_mst_branch will also stay allocated in memory until port #3's
 * malloc refcount reaches 0.
 *
 * This relationship is necessary because in order to release payload #2, we
 * need to be able to figure out the last relative of port #3 that's still
 * connected to the topology. In this case, we would travel up the topology as
 * shown below.
 *
 * .. kernel-figure:: dp-mst/topology-figure-3.dot
 *
 * And finally, remove payload #2 by communicating with port #2 through
 * sideband transactions.
 */

/**
 * drm_dp_mst_get_mstb_malloc() - Increment the malloc refcount of a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to increment the malloc refcount of
 *
 * Increments &drm_dp_mst_branch.malloc_kref. When
 * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
 * will be released and @mstb may no longer be used.
 *
 * See also: drm_dp_mst_put_mstb_malloc()
 */
static void
drm_dp_mst_get_mstb_malloc(struct drm_dp_mst_branch *mstb)
{
	kref_get(&mstb->malloc_kref);
	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref));
}

/**
 * drm_dp_mst_put_mstb_malloc() - Decrement the malloc refcount of a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to decrement the malloc refcount of
 *
 * Decrements &drm_dp_mst_branch.malloc_kref. When
 * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
 * will be released and @mstb may no longer be used.
 *
 * See also: drm_dp_mst_get_mstb_malloc()
 */
static void
drm_dp_mst_put_mstb_malloc(struct drm_dp_mst_branch *mstb)
{
	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref) - 1);
	kref_put(&mstb->malloc_kref, drm_dp_free_mst_branch_device);
}

static void drm_dp_free_mst_port(struct kref *kref)
{
	struct drm_dp_mst_port *port =
		container_of(kref, struct drm_dp_mst_port, malloc_kref);

	drm_dp_mst_put_mstb_malloc(port->parent);
	kfree(port);
}

/**
 * drm_dp_mst_get_port_malloc() - Increment the malloc refcount of an MST port
 * @port: The &struct drm_dp_mst_port to increment the malloc refcount of
 *
 * Increments &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
 * reaches 0, the memory allocation for @port will be released and @port may
 * no longer be used.
 *
 * Because @port could potentially be freed at any time by the DP MST helpers
 * if &drm_dp_mst_port.malloc_kref reaches 0, including during a call to this
 * function, drivers that which to make use of &struct drm_dp_mst_port should
 * ensure that they grab at least one main malloc reference to their MST ports
 * in &drm_dp_mst_topology_cbs.add_connector. This callback is called before
 * there is any chance for &drm_dp_mst_port.malloc_kref to reach 0.
 *
 * See also: drm_dp_mst_put_port_malloc()
 */
void
drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port)
{
	kref_get(&port->malloc_kref);
	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->malloc_kref));
}
EXPORT_SYMBOL(drm_dp_mst_get_port_malloc);

/**
 * drm_dp_mst_put_port_malloc() - Decrement the malloc refcount of an MST port
 * @port: The &struct drm_dp_mst_port to decrement the malloc refcount of
 *
 * Decrements &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
 * reaches 0, the memory allocation for @port will be released and @port may
 * no longer be used.
 *
 * See also: drm_dp_mst_get_port_malloc()
 */
void
drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port)
{
	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->malloc_kref) - 1);
	kref_put(&port->malloc_kref, drm_dp_free_mst_port);
}
EXPORT_SYMBOL(drm_dp_mst_put_port_malloc);

#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)

#define STACK_DEPTH 8

static noinline void
__topology_ref_save(struct drm_dp_mst_topology_mgr *mgr,
		    struct drm_dp_mst_topology_ref_history *history,
		    enum drm_dp_mst_topology_ref_type type)
{
	struct drm_dp_mst_topology_ref_entry *entry = NULL;
	depot_stack_handle_t backtrace;
	ulong stack_entries[STACK_DEPTH];
	uint n;
	int i;

	n = stack_trace_save(stack_entries, ARRAY_SIZE(stack_entries), 1);
	backtrace = stack_depot_save(stack_entries, n, GFP_KERNEL);
	if (!backtrace)
		return;

	/* Try to find an existing entry for this backtrace */
	for (i = 0; i < history->len; i++) {
		if (history->entries[i].backtrace == backtrace) {
			entry = &history->entries[i];
			break;
		}
	}

	/* Otherwise add one */
	if (!entry) {
		struct drm_dp_mst_topology_ref_entry *new;
		int new_len = history->len + 1;

		new = krealloc(history->entries, sizeof(*new) * new_len,
			       GFP_KERNEL);
		if (!new)
			return;

		entry = &new[history->len];
		history->len = new_len;
		history->entries = new;

		entry->backtrace = backtrace;
		entry->type = type;
		entry->count = 0;
	}
	entry->count++;
	entry->ts_nsec = ktime_get_ns();
}

static int
topology_ref_history_cmp(const void *a, const void *b)
{
	const struct drm_dp_mst_topology_ref_entry *entry_a = a, *entry_b = b;

	if (entry_a->ts_nsec > entry_b->ts_nsec)
		return 1;
	else if (entry_a->ts_nsec < entry_b->ts_nsec)
		return -1;
	else
		return 0;
}

static inline const char *
topology_ref_type_to_str(enum drm_dp_mst_topology_ref_type type)
{
	if (type == DRM_DP_MST_TOPOLOGY_REF_GET)
		return "get";
	else
		return "put";
}

static void
__dump_topology_ref_history(struct drm_dp_mst_topology_ref_history *history,
			    void *ptr, const char *type_str)
{
	struct drm_printer p = drm_debug_printer(DBG_PREFIX);
	char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
	int i;

	if (!buf)
		return;

	if (!history->len)
		goto out;

	/* First, sort the list so that it goes from oldest to newest
	 * reference entry
	 */
	sort(history->entries, history->len, sizeof(*history->entries),
	     topology_ref_history_cmp, NULL);

	drm_printf(&p, "%s (%p) topology count reached 0, dumping history:\n",
		   type_str, ptr);

	for (i = 0; i < history->len; i++) {
		const struct drm_dp_mst_topology_ref_entry *entry =
			&history->entries[i];
		u64 ts_nsec = entry->ts_nsec;
		u32 rem_nsec = do_div(ts_nsec, 1000000000);

		stack_depot_snprint(entry->backtrace, buf, PAGE_SIZE, 4);

		drm_printf(&p, "  %d %ss (last at %5llu.%06u):\n%s",
			   entry->count,
			   topology_ref_type_to_str(entry->type),
			   ts_nsec, rem_nsec / 1000, buf);
	}

	/* Now free the history, since this is the only time we expose it */
	kfree(history->entries);
out:
	kfree(buf);
}

static __always_inline void
drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb)
{
	__dump_topology_ref_history(&mstb->topology_ref_history, mstb,
				    "MSTB");
}

static __always_inline void
drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port)
{
	__dump_topology_ref_history(&port->topology_ref_history, port,
				    "Port");
}

static __always_inline void
save_mstb_topology_ref(struct drm_dp_mst_branch *mstb,
		       enum drm_dp_mst_topology_ref_type type)
{
	__topology_ref_save(mstb->mgr, &mstb->topology_ref_history, type);
}

static __always_inline void
save_port_topology_ref(struct drm_dp_mst_port *port,
		       enum drm_dp_mst_topology_ref_type type)
{
	__topology_ref_save(port->mgr, &port->topology_ref_history, type);
}

static inline void
topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr)
{
	mutex_lock(&mgr->topology_ref_history_lock);
}

static inline void
topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr)
{
	mutex_unlock(&mgr->topology_ref_history_lock);
}
#else
static inline void
topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr) {}
static inline void
topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr) {}
static inline void
drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb) {}
static inline void
drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port) {}
#define save_mstb_topology_ref(mstb, type)
#define save_port_topology_ref(port, type)
#endif

static void drm_dp_destroy_mst_branch_device(struct kref *kref)
{
	struct drm_dp_mst_branch *mstb =
		container_of(kref, struct drm_dp_mst_branch, topology_kref);
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;

	drm_dp_mst_dump_mstb_topology_history(mstb);

	INIT_LIST_HEAD(&mstb->destroy_next);

	/*
	 * This can get called under mgr->mutex, so we need to perform the
	 * actual destruction of the mstb in another worker
	 */
	mutex_lock(&mgr->delayed_destroy_lock);
	list_add(&mstb->destroy_next, &mgr->destroy_branch_device_list);
	mutex_unlock(&mgr->delayed_destroy_lock);
	queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
}

/**
 * drm_dp_mst_topology_try_get_mstb() - Increment the topology refcount of a
 * branch device unless it's zero
 * @mstb: &struct drm_dp_mst_branch to increment the topology refcount of
 *
 * Attempts to grab a topology reference to @mstb, if it hasn't yet been
 * removed from the topology (e.g. &drm_dp_mst_branch.topology_kref has
 * reached 0). Holding a topology reference implies that a malloc reference
 * will be held to @mstb as long as the user holds the topology reference.
 *
 * Care should be taken to ensure that the user has at least one malloc
 * reference to @mstb. If you already have a topology reference to @mstb, you
 * should use drm_dp_mst_topology_get_mstb() instead.
 *
 * See also:
 * drm_dp_mst_topology_get_mstb()
 * drm_dp_mst_topology_put_mstb()
 *
 * Returns:
 * * 1: A topology reference was grabbed successfully
 * * 0: @port is no longer in the topology, no reference was grabbed
 */
static int __must_check
drm_dp_mst_topology_try_get_mstb(struct drm_dp_mst_branch *mstb)
{
	int ret;

	topology_ref_history_lock(mstb->mgr);
	ret = kref_get_unless_zero(&mstb->topology_kref);
	if (ret) {
		drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));
		save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
	}

	topology_ref_history_unlock(mstb->mgr);

	return ret;
}

/**
 * drm_dp_mst_topology_get_mstb() - Increment the topology refcount of a
 * branch device
 * @mstb: The &struct drm_dp_mst_branch to increment the topology refcount of
 *
 * Increments &drm_dp_mst_branch.topology_refcount without checking whether or
 * not it's already reached 0. This is only valid to use in scenarios where
 * you are already guaranteed to have at least one active topology reference
 * to @mstb. Otherwise, drm_dp_mst_topology_try_get_mstb() must be used.
 *
 * See also:
 * drm_dp_mst_topology_try_get_mstb()
 * drm_dp_mst_topology_put_mstb()
 */
static void drm_dp_mst_topology_get_mstb(struct drm_dp_mst_branch *mstb)
{
	topology_ref_history_lock(mstb->mgr);

	save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
	WARN_ON(kref_read(&mstb->topology_kref) == 0);
	kref_get(&mstb->topology_kref);
	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));

	topology_ref_history_unlock(mstb->mgr);
}

/**
 * drm_dp_mst_topology_put_mstb() - release a topology reference to a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to release the topology reference from
 *
 * Releases a topology reference from @mstb by decrementing
 * &drm_dp_mst_branch.topology_kref.
 *
 * See also:
 * drm_dp_mst_topology_try_get_mstb()
 * drm_dp_mst_topology_get_mstb()
 */
static void
drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
{
	topology_ref_history_lock(mstb->mgr);

	drm_dbg(mstb->mgr->dev, "mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref) - 1);
	save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_PUT);

	topology_ref_history_unlock(mstb->mgr);
	kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
}

static void drm_dp_destroy_port(struct kref *kref)
{
	struct drm_dp_mst_port *port =
		container_of(kref, struct drm_dp_mst_port, topology_kref);
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;

	drm_dp_mst_dump_port_topology_history(port);

	/* There's nothing that needs locking to destroy an input port yet */
	if (port->input) {
		drm_dp_mst_put_port_malloc(port);
		return;
	}

	kfree(port->cached_edid);

	/*
	 * we can't destroy the connector here, as we might be holding the
	 * mode_config.mutex from an EDID retrieval
	 */
	mutex_lock(&mgr->delayed_destroy_lock);
	list_add(&port->next, &mgr->destroy_port_list);
	mutex_unlock(&mgr->delayed_destroy_lock);
	queue_work(mgr->delayed_destroy_wq, &mgr->delayed_destroy_work);
}

/**
 * drm_dp_mst_topology_try_get_port() - Increment the topology refcount of a
 * port unless it's zero
 * @port: &struct drm_dp_mst_port to increment the topology refcount of
 *
 * Attempts to grab a topology reference to @port, if it hasn't yet been
 * removed from the topology (e.g. &drm_dp_mst_port.topology_kref has reached
 * 0). Holding a topology reference implies that a malloc reference will be
 * held to @port as long as the user holds the topology reference.
 *
 * Care should be taken to ensure that the user has at least one malloc
 * reference to @port. If you already have a topology reference to @port, you
 * should use drm_dp_mst_topology_get_port() instead.
 *
 * See also:
 * drm_dp_mst_topology_get_port()
 * drm_dp_mst_topology_put_port()
 *
 * Returns:
 * * 1: A topology reference was grabbed successfully
 * * 0: @port is no longer in the topology, no reference was grabbed
 */
static int __must_check
drm_dp_mst_topology_try_get_port(struct drm_dp_mst_port *port)
{
	int ret;

	topology_ref_history_lock(port->mgr);
	ret = kref_get_unless_zero(&port->topology_kref);
	if (ret) {
		drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref));
		save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);
	}

	topology_ref_history_unlock(port->mgr);
	return ret;
}

/**
 * drm_dp_mst_topology_get_port() - Increment the topology refcount of a port
 * @port: The &struct drm_dp_mst_port to increment the topology refcount of
 *
 * Increments &drm_dp_mst_port.topology_refcount without checking whether or
 * not it's already reached 0. This is only valid to use in scenarios where
 * you are already guaranteed to have at least one active topology reference
 * to @port. Otherwise, drm_dp_mst_topology_try_get_port() must be used.
 *
 * See also:
 * drm_dp_mst_topology_try_get_port()
 * drm_dp_mst_topology_put_port()
 */
static void drm_dp_mst_topology_get_port(struct drm_dp_mst_port *port)
{
	topology_ref_history_lock(port->mgr);

	WARN_ON(kref_read(&port->topology_kref) == 0);
	kref_get(&port->topology_kref);
	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref));
	save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);

	topology_ref_history_unlock(port->mgr);
}

/**
 * drm_dp_mst_topology_put_port() - release a topology reference to a port
 * @port: The &struct drm_dp_mst_port to release the topology reference from
 *
 * Releases a topology reference from @port by decrementing
 * &drm_dp_mst_port.topology_kref.
 *
 * See also:
 * drm_dp_mst_topology_try_get_port()
 * drm_dp_mst_topology_get_port()
 */
static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
{
	topology_ref_history_lock(port->mgr);

	drm_dbg(port->mgr->dev, "port %p (%d)\n", port, kref_read(&port->topology_kref) - 1);
	save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_PUT);

	topology_ref_history_unlock(port->mgr);
	kref_put(&port->topology_kref, drm_dp_destroy_port);
}

static struct drm_dp_mst_branch *
drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
					      struct drm_dp_mst_branch *to_find)
{
	struct drm_dp_mst_port *port;
	struct drm_dp_mst_branch *rmstb;

	if (to_find == mstb)
		return mstb;

	list_for_each_entry(port, &mstb->ports, next) {
		if (port->mstb) {
			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
			    port->mstb, to_find);
			if (rmstb)
				return rmstb;
		}
	}
	return NULL;
}

static struct drm_dp_mst_branch *
drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
				       struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_branch *rmstb = NULL;

	mutex_lock(&mgr->lock);
	if (mgr->mst_primary) {
		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
		    mgr->mst_primary, mstb);

		if (rmstb && !drm_dp_mst_topology_try_get_mstb(rmstb))
			rmstb = NULL;
	}
	mutex_unlock(&mgr->lock);
	return rmstb;
}

static struct drm_dp_mst_port *
drm_dp_mst_topology_get_port_validated_locked(struct drm_dp_mst_branch *mstb,
					      struct drm_dp_mst_port *to_find)
{
	struct drm_dp_mst_port *port, *mport;

	list_for_each_entry(port, &mstb->ports, next) {
		if (port == to_find)
			return port;

		if (port->mstb) {
			mport = drm_dp_mst_topology_get_port_validated_locked(
			    port->mstb, to_find);
			if (mport)
				return mport;
		}
	}
	return NULL;
}

static struct drm_dp_mst_port *
drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
				       struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_port *rport = NULL;

	mutex_lock(&mgr->lock);
	if (mgr->mst_primary) {
		rport = drm_dp_mst_topology_get_port_validated_locked(
		    mgr->mst_primary, port);

		if (rport && !drm_dp_mst_topology_try_get_port(rport))
			rport = NULL;
	}
	mutex_unlock(&mgr->lock);
	return rport;
}

static struct drm_dp_mst_port *drm_dp_get_port(struct drm_dp_mst_branch *mstb, u8 port_num)
{
	struct drm_dp_mst_port *port;
	int ret;

	list_for_each_entry(port, &mstb->ports, next) {
		if (port->port_num == port_num) {
			ret = drm_dp_mst_topology_try_get_port(port);
			return ret ? port : NULL;
		}
	}

	return NULL;
}

/*
 * calculate a new RAD for this MST branch device
 * if parent has an LCT of 2 then it has 1 nibble of RAD,
 * if parent has an LCT of 3 then it has 2 nibbles of RAD,
 */
static u8 drm_dp_calculate_rad(struct drm_dp_mst_port *port,
				 u8 *rad)
{
	int parent_lct = port->parent->lct;
	int shift = 4;
	int idx = (parent_lct - 1) / 2;

	if (parent_lct > 1) {
		memcpy(rad, port->parent->rad, idx + 1);
		shift = (parent_lct % 2) ? 4 : 0;
	} else
		rad[0] = 0;

	rad[idx] |= port->port_num << shift;
	return parent_lct + 1;
}

static bool drm_dp_mst_is_end_device(u8 pdt, bool mcs)
{
	switch (pdt) {
	case DP_PEER_DEVICE_DP_LEGACY_CONV:
	case DP_PEER_DEVICE_SST_SINK:
		return true;
	case DP_PEER_DEVICE_MST_BRANCHING:
		/* For sst branch device */
		if (!mcs)
			return true;

		return false;
	}
	return true;
}

static int
drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
		    bool new_mcs)
{
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	struct drm_dp_mst_branch *mstb;
	u8 rad[8], lct;
	int ret = 0;

	if (port->pdt == new_pdt && port->mcs == new_mcs)
		return 0;

	/* Teardown the old pdt, if there is one */
	if (port->pdt != DP_PEER_DEVICE_NONE) {
		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
			/*
			 * If the new PDT would also have an i2c bus,
			 * don't bother with reregistering it
			 */
			if (new_pdt != DP_PEER_DEVICE_NONE &&
			    drm_dp_mst_is_end_device(new_pdt, new_mcs)) {
				port->pdt = new_pdt;
				port->mcs = new_mcs;
				return 0;
			}

			/* remove i2c over sideband */
			drm_dp_mst_unregister_i2c_bus(port);
		} else {
			mutex_lock(&mgr->lock);
			drm_dp_mst_topology_put_mstb(port->mstb);
			port->mstb = NULL;
			mutex_unlock(&mgr->lock);
		}
	}

	port->pdt = new_pdt;
	port->mcs = new_mcs;

	if (port->pdt != DP_PEER_DEVICE_NONE) {
		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
			/* add i2c over sideband */
			ret = drm_dp_mst_register_i2c_bus(port);
		} else {
			lct = drm_dp_calculate_rad(port, rad);
			mstb = drm_dp_add_mst_branch_device(lct, rad);
			if (!mstb) {
				ret = -ENOMEM;
				drm_err(mgr->dev, "Failed to create MSTB for port %p", port);
				goto out;
			}

			mutex_lock(&mgr->lock);
			port->mstb = mstb;
			mstb->mgr = port->mgr;
			mstb->port_parent = port;

			/*
			 * Make sure this port's memory allocation stays
			 * around until its child MSTB releases it
			 */
			drm_dp_mst_get_port_malloc(port);
			mutex_unlock(&mgr->lock);

			/* And make sure we send a link address for this */
			ret = 1;
		}
	}

out:
	if (ret < 0)
		port->pdt = DP_PEER_DEVICE_NONE;
	return ret;
}

/**
 * drm_dp_mst_dpcd_read() - read a series of bytes from the DPCD via sideband
 * @aux: Fake sideband AUX CH
 * @offset: address of the (first) register to read
 * @buffer: buffer to store the register values
 * @size: number of bytes in @buffer
 *
 * Performs the same functionality for remote devices via
 * sideband messaging as drm_dp_dpcd_read() does for local
 * devices via actual AUX CH.
 *
 * Return: Number of bytes read, or negative error code on failure.
 */
ssize_t drm_dp_mst_dpcd_read(struct drm_dp_aux *aux,
			     unsigned int offset, void *buffer, size_t size)
{
	struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
						    aux);

	return drm_dp_send_dpcd_read(port->mgr, port,
				     offset, size, buffer);
}

/**
 * drm_dp_mst_dpcd_write() - write a series of bytes to the DPCD via sideband
 * @aux: Fake sideband AUX CH
 * @offset: address of the (first) register to write
 * @buffer: buffer containing the values to write
 * @size: number of bytes in @buffer
 *
 * Performs the same functionality for remote devices via
 * sideband messaging as drm_dp_dpcd_write() does for local
 * devices via actual AUX CH.
 *
 * Return: number of bytes written on success, negative error code on failure.
 */
ssize_t drm_dp_mst_dpcd_write(struct drm_dp_aux *aux,
			      unsigned int offset, void *buffer, size_t size)
{
	struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
						    aux);

	return drm_dp_send_dpcd_write(port->mgr, port,
				      offset, size, buffer);
}

static int drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, u8 *guid)
{
	int ret = 0;

	memcpy(mstb->guid, guid, 16);

	if (!drm_dp_validate_guid(mstb->mgr, mstb->guid)) {
		if (mstb->port_parent) {
			ret = drm_dp_send_dpcd_write(mstb->mgr,
						     mstb->port_parent,
						     DP_GUID, 16, mstb->guid);
		} else {
			ret = drm_dp_dpcd_write(mstb->mgr->aux,
						DP_GUID, mstb->guid, 16);
		}
	}

	if (ret < 16 && ret > 0)
		return -EPROTO;

	return ret == 16 ? 0 : ret;
}

static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb,
				int pnum,
				char *proppath,
				size_t proppath_size)
{
	int i;
	char temp[8];

	snprintf(proppath, proppath_size, "mst:%d", mstb->mgr->conn_base_id);
	for (i = 0; i < (mstb->lct - 1); i++) {
		int shift = (i % 2) ? 0 : 4;
		int port_num = (mstb->rad[i / 2] >> shift) & 0xf;

		snprintf(temp, sizeof(temp), "-%d", port_num);
		strlcat(proppath, temp, proppath_size);
	}
	snprintf(temp, sizeof(temp), "-%d", pnum);
	strlcat(proppath, temp, proppath_size);
}

/**
 * drm_dp_mst_connector_late_register() - Late MST connector registration
 * @connector: The MST connector
 * @port: The MST port for this connector
 *
 * Helper to register the remote aux device for this MST port. Drivers should
 * call this from their mst connector's late_register hook to enable MST aux
 * devices.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_dp_mst_connector_late_register(struct drm_connector *connector,
				       struct drm_dp_mst_port *port)
{
	drm_dbg_kms(port->mgr->dev, "registering %s remote bus for %s\n",
		    port->aux.name, connector->kdev->kobj.name);

	port->aux.dev = connector->kdev;
	return drm_dp_aux_register_devnode(&port->aux);
}
EXPORT_SYMBOL(drm_dp_mst_connector_late_register);

/**
 * drm_dp_mst_connector_early_unregister() - Early MST connector unregistration
 * @connector: The MST connector
 * @port: The MST port for this connector
 *
 * Helper to unregister the remote aux device for this MST port, registered by
 * drm_dp_mst_connector_late_register(). Drivers should call this from their mst
 * connector's early_unregister hook.
 */
void drm_dp_mst_connector_early_unregister(struct drm_connector *connector,
					   struct drm_dp_mst_port *port)
{
	drm_dbg_kms(port->mgr->dev, "unregistering %s remote bus for %s\n",
		    port->aux.name, connector->kdev->kobj.name);
	drm_dp_aux_unregister_devnode(&port->aux);
}
EXPORT_SYMBOL(drm_dp_mst_connector_early_unregister);

static void
drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
			      struct drm_dp_mst_port *port)
{
	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
	char proppath[255];
	int ret;

	build_mst_prop_path(mstb, port->port_num, proppath, sizeof(proppath));
	port->connector = mgr->cbs->add_connector(mgr, port, proppath);
	if (!port->connector) {
		ret = -ENOMEM;
		goto error;
	}

	if (port->pdt != DP_PEER_DEVICE_NONE &&
	    drm_dp_mst_is_end_device(port->pdt, port->mcs) &&
	    port->port_num >= DP_MST_LOGICAL_PORT_0)
		port->cached_edid = drm_get_edid(port->connector,
						 &port->aux.ddc);

	drm_connector_register(port->connector);
	return;

error:
	drm_err(mgr->dev, "Failed to create connector for port %p: %d\n", port, ret);
}

/*
 * Drop a topology reference, and unlink the port from the in-memory topology
 * layout
 */
static void
drm_dp_mst_topology_unlink_port(struct drm_dp_mst_topology_mgr *mgr,
				struct drm_dp_mst_port *port)
{
	mutex_lock(&mgr->lock);
	port->parent->num_ports--;
	list_del(&port->next);
	mutex_unlock(&mgr->lock);
	drm_dp_mst_topology_put_port(port);
}

static struct drm_dp_mst_port *
drm_dp_mst_add_port(struct drm_device *dev,
		    struct drm_dp_mst_topology_mgr *mgr,
		    struct drm_dp_mst_branch *mstb, u8 port_number)
{
	struct drm_dp_mst_port *port = kzalloc(sizeof(*port), GFP_KERNEL);

	if (!port)
		return NULL;

	kref_init(&port->topology_kref);
	kref_init(&port->malloc_kref);
	port->parent = mstb;
	port->port_num = port_number;
	port->mgr = mgr;
	port->aux.name = "DPMST";
	port->aux.dev = dev->dev;
	port->aux.is_remote = true;

	/* initialize the MST downstream port's AUX crc work queue */
	port->aux.drm_dev = dev;
	drm_dp_remote_aux_init(&port->aux);

	/*
	 * Make sure the memory allocation for our parent branch stays
	 * around until our own memory allocation is released
	 */
	drm_dp_mst_get_mstb_malloc(mstb);

	return port;
}

static int
drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
				    struct drm_device *dev,
				    struct drm_dp_link_addr_reply_port *port_msg)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	struct drm_dp_mst_port *port;
	int old_ddps = 0, ret;
	u8 new_pdt = DP_PEER_DEVICE_NONE;
	bool new_mcs = 0;
	bool created = false, send_link_addr = false, changed = false;

	port = drm_dp_get_port(mstb, port_msg->port_number);
	if (!port) {
		port = drm_dp_mst_add_port(dev, mgr, mstb,
					   port_msg->port_number);
		if (!port)
			return -ENOMEM;
		created = true;
		changed = true;
	} else if (!port->input && port_msg->input_port && port->connector) {
		/* Since port->connector can't be changed here, we create a
		 * new port if input_port changes from 0 to 1
		 */
		drm_dp_mst_topology_unlink_port(mgr, port);
		drm_dp_mst_topology_put_port(port);
		port = drm_dp_mst_add_port(dev, mgr, mstb,
					   port_msg->port_number);
		if (!port)
			return -ENOMEM;
		changed = true;
		created = true;
	} else if (port->input && !port_msg->input_port) {
		changed = true;
	} else if (port->connector) {
		/* We're updating a port that's exposed to userspace, so do it
		 * under lock
		 */
		drm_modeset_lock(&mgr->base.lock, NULL);

		old_ddps = port->ddps;
		changed = port->ddps != port_msg->ddps ||
			(port->ddps &&
			 (port->ldps != port_msg->legacy_device_plug_status ||
			  port->dpcd_rev != port_msg->dpcd_revision ||
			  port->mcs != port_msg->mcs ||
			  port->pdt != port_msg->peer_device_type ||
			  port->num_sdp_stream_sinks !=
			  port_msg->num_sdp_stream_sinks));
	}

	port->input = port_msg->input_port;
	if (!port->input)
		new_pdt = port_msg->peer_device_type;
	new_mcs = port_msg->mcs;
	port->ddps = port_msg->ddps;
	port->ldps = port_msg->legacy_device_plug_status;
	port->dpcd_rev = port_msg->dpcd_revision;
	port->num_sdp_streams = port_msg->num_sdp_streams;
	port->num_sdp_stream_sinks = port_msg->num_sdp_stream_sinks;

	/* manage mstb port lists with mgr lock - take a reference
	   for this list */
	if (created) {
		mutex_lock(&mgr->lock);
		drm_dp_mst_topology_get_port(port);
		list_add(&port->next, &mstb->ports);
		mstb->num_ports++;
		mutex_unlock(&mgr->lock);
	}

	/*
	 * Reprobe PBN caps on both hotplug, and when re-probing the link
	 * for our parent mstb
	 */
	if (old_ddps != port->ddps || !created) {
		if (port->ddps && !port->input) {
			ret = drm_dp_send_enum_path_resources(mgr, mstb,
							      port);
			if (ret == 1)
				changed = true;
		} else {
			port->full_pbn = 0;
		}
	}

	ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
	if (ret == 1) {
		send_link_addr = true;
	} else if (ret < 0) {
		drm_err(dev, "Failed to change PDT on port %p: %d\n", port, ret);
		goto fail;
	}

	/*
	 * If this port wasn't just created, then we're reprobing because
	 * we're coming out of suspend. In this case, always resend the link
	 * address if there's an MSTB on this port
	 */
	if (!created && port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
	    port->mcs)
		send_link_addr = true;

	if (port->connector)
		drm_modeset_unlock(&mgr->base.lock);
	else if (!port->input)
		drm_dp_mst_port_add_connector(mstb, port);

	if (send_link_addr && port->mstb) {
		ret = drm_dp_send_link_address(mgr, port->mstb);
		if (ret == 1) /* MSTB below us changed */
			changed = true;
		else if (ret < 0)
			goto fail_put;
	}

	/* put reference to this port */
	drm_dp_mst_topology_put_port(port);
	return changed;

fail:
	drm_dp_mst_topology_unlink_port(mgr, port);
	if (port->connector)
		drm_modeset_unlock(&mgr->base.lock);
fail_put:
	drm_dp_mst_topology_put_port(port);
	return ret;
}

static void
drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
			    struct drm_dp_connection_status_notify *conn_stat)
{
	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
	struct drm_dp_mst_port *port;
	int old_ddps, ret;
	u8 new_pdt;
	bool new_mcs;
	bool dowork = false, create_connector = false;

	port = drm_dp_get_port(mstb, conn_stat->port_number);
	if (!port)
		return;

	if (port->connector) {
		if (!port->input && conn_stat->input_port) {
			/*
			 * We can't remove a connector from an already exposed
			 * port, so just throw the port out and make sure we
			 * reprobe the link address of it's parent MSTB
			 */
			drm_dp_mst_topology_unlink_port(mgr, port);
			mstb->link_address_sent = false;
			dowork = true;
			goto out;
		}

		/* Locking is only needed if the port's exposed to userspace */
		drm_modeset_lock(&mgr->base.lock, NULL);
	} else if (port->input && !conn_stat->input_port) {
		create_connector = true;
		/* Reprobe link address so we get num_sdp_streams */
		mstb->link_address_sent = false;
		dowork = true;
	}

	old_ddps = port->ddps;
	port->input = conn_stat->input_port;
	port->ldps = conn_stat->legacy_device_plug_status;
	port->ddps = conn_stat->displayport_device_plug_status;

	if (old_ddps != port->ddps) {
		if (port->ddps && !port->input)
			drm_dp_send_enum_path_resources(mgr, mstb, port);
		else
			port->full_pbn = 0;
	}

	new_pdt = port->input ? DP_PEER_DEVICE_NONE : conn_stat->peer_device_type;
	new_mcs = conn_stat->message_capability_status;
	ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
	if (ret == 1) {
		dowork = true;
	} else if (ret < 0) {
		drm_err(mgr->dev, "Failed to change PDT for port %p: %d\n", port, ret);
		dowork = false;
	}

	if (port->connector)
		drm_modeset_unlock(&mgr->base.lock);
	else if (create_connector)
		drm_dp_mst_port_add_connector(mstb, port);

out:
	drm_dp_mst_topology_put_port(port);
	if (dowork)
		queue_work(system_long_wq, &mstb->mgr->work);
}

static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
							       u8 lct, u8 *rad)
{
	struct drm_dp_mst_branch *mstb;
	struct drm_dp_mst_port *port;
	int i, ret;
	/* find the port by iterating down */

	mutex_lock(&mgr->lock);
	mstb = mgr->mst_primary;

	if (!mstb)
		goto out;

	for (i = 0; i < lct - 1; i++) {
		int shift = (i % 2) ? 0 : 4;
		int port_num = (rad[i / 2] >> shift) & 0xf;

		list_for_each_entry(port, &mstb->ports, next) {
			if (port->port_num == port_num) {
				mstb = port->mstb;
				if (!mstb) {
					drm_err(mgr->dev,
						"failed to lookup MSTB with lct %d, rad %02x\n",
						lct, rad[0]);
					goto out;
				}

				break;
			}
		}
	}
	ret = drm_dp_mst_topology_try_get_mstb(mstb);
	if (!ret)
		mstb = NULL;
out:
	mutex_unlock(&mgr->lock);
	return mstb;
}

static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
	struct drm_dp_mst_branch *mstb,
	const uint8_t *guid)
{
	struct drm_dp_mst_branch *found_mstb;
	struct drm_dp_mst_port *port;

	if (memcmp(mstb->guid, guid, 16) == 0)
		return mstb;


	list_for_each_entry(port, &mstb->ports, next) {
		if (!port->mstb)
			continue;

		found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);

		if (found_mstb)
			return found_mstb;
	}

	return NULL;
}

static struct drm_dp_mst_branch *
drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
				     const uint8_t *guid)
{
	struct drm_dp_mst_branch *mstb;
	int ret;

	/* find the port by iterating down */
	mutex_lock(&mgr->lock);

	mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
	if (mstb) {
		ret = drm_dp_mst_topology_try_get_mstb(mstb);
		if (!ret)
			mstb = NULL;
	}

	mutex_unlock(&mgr->lock);
	return mstb;
}

static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
					       struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_mst_port *port;
	int ret;
	bool changed = false;

	if (!mstb->link_address_sent) {
		ret = drm_dp_send_link_address(mgr, mstb);
		if (ret == 1)
			changed = true;
		else if (ret < 0)
			return ret;
	}

	list_for_each_entry(port, &mstb->ports, next) {
		struct drm_dp_mst_branch *mstb_child = NULL;

		if (port->input || !port->ddps)
			continue;

		if (port->mstb)
			mstb_child = drm_dp_mst_topology_get_mstb_validated(
			    mgr, port->mstb);

		if (mstb_child) {
			ret = drm_dp_check_and_send_link_address(mgr,
								 mstb_child);
			drm_dp_mst_topology_put_mstb(mstb_child);
			if (ret == 1)
				changed = true;
			else if (ret < 0)
				return ret;
		}
	}

	return changed;
}

static void drm_dp_mst_link_probe_work(struct work_struct *work)
{
	struct drm_dp_mst_topology_mgr *mgr =
		container_of(work, struct drm_dp_mst_topology_mgr, work);
	struct drm_device *dev = mgr->dev;
	struct drm_dp_mst_branch *mstb;
	int ret;
	bool clear_payload_id_table;

	mutex_lock(&mgr->probe_lock);

	mutex_lock(&mgr->lock);
	clear_payload_id_table = !mgr->payload_id_table_cleared;
	mgr->payload_id_table_cleared = true;

	mstb = mgr->mst_primary;
	if (mstb) {
		ret = drm_dp_mst_topology_try_get_mstb(mstb);
		if (!ret)
			mstb = NULL;
	}
	mutex_unlock(&mgr->lock);
	if (!mstb) {
		mutex_unlock(&mgr->probe_lock);
		return;
	}

	/*
	 * Certain branch devices seem to incorrectly report an available_pbn
	 * of 0 on downstream sinks, even after clearing the
	 * DP_PAYLOAD_ALLOCATE_* registers in
	 * drm_dp_mst_topology_mgr_set_mst(). Namely, the CableMatters USB-C
	 * 2x DP hub. Sending a CLEAR_PAYLOAD_ID_TABLE message seems to make
	 * things work again.
	 */
	if (clear_payload_id_table) {
		drm_dbg_kms(dev, "Clearing payload ID table\n");
		drm_dp_send_clear_payload_id_table(mgr, mstb);
	}

	ret = drm_dp_check_and_send_link_address(mgr, mstb);
	drm_dp_mst_topology_put_mstb(mstb);

	mutex_unlock(&mgr->probe_lock);
	if (ret > 0)
		drm_kms_helper_hotplug_event(dev);
}

static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
				 u8 *guid)
{
	u64 salt;

	if (memchr_inv(guid, 0, 16))
		return true;

	salt = get_jiffies_64();

	memcpy(&guid[0], &salt, sizeof(u64));
	memcpy(&guid[8], &salt, sizeof(u64));

	return false;
}

static void build_dpcd_read(struct drm_dp_sideband_msg_tx *msg,
			    u8 port_num, u32 offset, u8 num_bytes)
{
	struct drm_dp_sideband_msg_req_body req;

	req.req_type = DP_REMOTE_DPCD_READ;
	req.u.dpcd_read.port_number = port_num;
	req.u.dpcd_read.dpcd_address = offset;
	req.u.dpcd_read.num_bytes = num_bytes;
	drm_dp_encode_sideband_req(&req, msg);
}

static int drm_dp_send_sideband_msg(struct drm_dp_mst_topology_mgr *mgr,
				    bool up, u8 *msg, int len)
{
	int ret;
	int regbase = up ? DP_SIDEBAND_MSG_UP_REP_BASE : DP_SIDEBAND_MSG_DOWN_REQ_BASE;
	int tosend, total, offset;
	int retries = 0;

retry:
	total = len;
	offset = 0;
	do {
		tosend = min3(mgr->max_dpcd_transaction_bytes, 16, total);

		ret = drm_dp_dpcd_write(mgr->aux, regbase + offset,
					&msg[offset],
					tosend);
		if (ret != tosend) {
			if (ret == -EIO && retries < 5) {
				retries++;
				goto retry;
			}
			drm_dbg_kms(mgr->dev, "failed to dpcd write %d %d\n", tosend, ret);

			return -EIO;
		}
		offset += tosend;
		total -= tosend;
	} while (total > 0);
	return 0;
}

static int set_hdr_from_dst_qlock(struct drm_dp_sideband_msg_hdr *hdr,
				  struct drm_dp_sideband_msg_tx *txmsg)
{
	struct drm_dp_mst_branch *mstb = txmsg->dst;
	u8 req_type;

	req_type = txmsg->msg[0] & 0x7f;
	if (req_type == DP_CONNECTION_STATUS_NOTIFY ||
		req_type == DP_RESOURCE_STATUS_NOTIFY ||
		req_type == DP_CLEAR_PAYLOAD_ID_TABLE)
		hdr->broadcast = 1;
	else
		hdr->broadcast = 0;
	hdr->path_msg = txmsg->path_msg;
	if (hdr->broadcast) {
		hdr->lct = 1;
		hdr->lcr = 6;
	} else {
		hdr->lct = mstb->lct;
		hdr->lcr = mstb->lct - 1;
	}

	memcpy(hdr->rad, mstb->rad, hdr->lct / 2);

	return 0;
}
/*
 * process a single block of the next message in the sideband queue
 */
static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
				   struct drm_dp_sideband_msg_tx *txmsg,
				   bool up)
{
	u8 chunk[48];
	struct drm_dp_sideband_msg_hdr hdr;
	int len, space, idx, tosend;
	int ret;

	if (txmsg->state == DRM_DP_SIDEBAND_TX_SENT)
		return 0;

	memset(&hdr, 0, sizeof(struct drm_dp_sideband_msg_hdr));

	if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED)
		txmsg->state = DRM_DP_SIDEBAND_TX_START_SEND;

	/* make hdr from dst mst */
	ret = set_hdr_from_dst_qlock(&hdr, txmsg);
	if (ret < 0)
		return ret;

	/* amount left to send in this message */
	len = txmsg->cur_len - txmsg->cur_offset;

	/* 48 - sideband msg size - 1 byte for data CRC, x header bytes */
	space = 48 - 1 - drm_dp_calc_sb_hdr_size(&hdr);

	tosend = min(len, space);
	if (len == txmsg->cur_len)
		hdr.somt = 1;
	if (space >= len)
		hdr.eomt = 1;


	hdr.msg_len = tosend + 1;
	drm_dp_encode_sideband_msg_hdr(&hdr, chunk, &idx);
	memcpy(&chunk[idx], &txmsg->msg[txmsg->cur_offset], tosend);
	/* add crc at end */
	drm_dp_crc_sideband_chunk_req(&chunk[idx], tosend);
	idx += tosend + 1;

	ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
	if (ret) {
		if (drm_debug_enabled(DRM_UT_DP)) {
			struct drm_printer p = drm_debug_printer(DBG_PREFIX);

			drm_printf(&p, "sideband msg failed to send\n");
			drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
		}
		return ret;
	}

	txmsg->cur_offset += tosend;
	if (txmsg->cur_offset == txmsg->cur_len) {
		txmsg->state = DRM_DP_SIDEBAND_TX_SENT;
		return 1;
	}
	return 0;
}

static void process_single_down_tx_qlock(struct drm_dp_mst_topology_mgr *mgr)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	int ret;

	WARN_ON(!mutex_is_locked(&mgr->qlock));

	/* construct a chunk from the first msg in the tx_msg queue */
	if (list_empty(&mgr->tx_msg_downq))
		return;

	txmsg = list_first_entry(&mgr->tx_msg_downq,
				 struct drm_dp_sideband_msg_tx, next);
	ret = process_single_tx_qlock(mgr, txmsg, false);
	if (ret < 0) {
		drm_dbg_kms(mgr->dev, "failed to send msg in q %d\n", ret);
		list_del(&txmsg->next);
		txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
		wake_up_all(&mgr->tx_waitq);
	}
}

static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
				 struct drm_dp_sideband_msg_tx *txmsg)
{
	mutex_lock(&mgr->qlock);
	list_add_tail(&txmsg->next, &mgr->tx_msg_downq);

	if (drm_debug_enabled(DRM_UT_DP)) {
		struct drm_printer p = drm_debug_printer(DBG_PREFIX);

		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
	}

	if (list_is_singular(&mgr->tx_msg_downq))
		process_single_down_tx_qlock(mgr);
	mutex_unlock(&mgr->qlock);
}

static void
drm_dp_dump_link_address(const struct drm_dp_mst_topology_mgr *mgr,
			 struct drm_dp_link_address_ack_reply *reply)
{
	struct drm_dp_link_addr_reply_port *port_reply;
	int i;

	for (i = 0; i < reply->nports; i++) {
		port_reply = &reply->ports[i];
		drm_dbg_kms(mgr->dev,
			    "port %d: input %d, pdt: %d, pn: %d, dpcd_rev: %02x, mcs: %d, ddps: %d, ldps %d, sdp %d/%d\n",
			    i,
			    port_reply->input_port,
			    port_reply->peer_device_type,
			    port_reply->port_number,
			    port_reply->dpcd_revision,
			    port_reply->mcs,
			    port_reply->ddps,
			    port_reply->legacy_device_plug_status,
			    port_reply->num_sdp_streams,
			    port_reply->num_sdp_stream_sinks);
	}
}

static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
				     struct drm_dp_mst_branch *mstb)
{
	struct drm_dp_sideband_msg_tx *txmsg;
	struct drm_dp_link_address_ack_reply *reply;
	struct drm_dp_mst_port *port, *tmp;
	int i, ret, port_mask = 0;
	bool changed = false;

	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);