blob: eaa6fb3224bc4809b5f4a883120f404968246096 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
/*
* Management Component Transport Protocol (MCTP) - serial transport
* binding. This driver is an implementation of the DMTF specificiation
* "DSP0253 - Management Component Transport Protocol (MCTP) Serial Transport
* Binding", available at:
*
* https://www.dmtf.org/sites/default/files/standards/documents/DSP0253_1.0.0.pdf
*
* This driver provides DSP0253-type MCTP-over-serial transport using a Linux
* tty device, by setting the N_MCTP line discipline on the tty.
*
* Copyright (c) 2021 Code Construct
*/
#include <linux/idr.h>
#include <linux/if_arp.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/tty.h>
#include <linux/workqueue.h>
#include <linux/crc-ccitt.h>
#include <linux/mctp.h>
#include <net/mctp.h>
#include <net/pkt_sched.h>
#define MCTP_SERIAL_MTU 68 /* base mtu (64) + mctp header */
#define MCTP_SERIAL_FRAME_MTU (MCTP_SERIAL_MTU + 6) /* + serial framing */
#define MCTP_SERIAL_VERSION 0x1 /* DSP0253 defines a single version: 1 */
#define BUFSIZE MCTP_SERIAL_FRAME_MTU
#define BYTE_FRAME 0x7e
#define BYTE_ESC 0x7d
static DEFINE_IDA(mctp_serial_ida);
enum mctp_serial_state {
STATE_IDLE,
STATE_START,
STATE_HEADER,
STATE_DATA,
STATE_ESCAPE,
STATE_TRAILER,
STATE_DONE,
STATE_ERR,
};
struct mctp_serial {
struct net_device *netdev;
struct tty_struct *tty;
int idx;
/* protects our rx & tx state machines; held during both paths */
spinlock_t lock;
struct work_struct tx_work;
enum mctp_serial_state txstate, rxstate;
u16 txfcs, rxfcs, rxfcs_rcvd;
unsigned int txlen, rxlen;
unsigned int txpos, rxpos;
unsigned char txbuf[BUFSIZE],
rxbuf[BUFSIZE];
};
static bool needs_escape(unsigned char c)
{
return c == BYTE_ESC || c == BYTE_FRAME;
}
static int next_chunk_len(struct mctp_serial *dev)
{
int i;
/* either we have no bytes to send ... */
if (dev->txpos == dev->txlen)
return 0;
/* ... or the next byte to send is an escaped byte; requiring a
* single-byte chunk...
*/
if (needs_escape(dev->txbuf[dev->txpos]))
return 1;
/* ... or we have one or more bytes up to the next escape - this chunk
* will be those non-escaped bytes, and does not include the escaped
* byte.
*/
for (i = 1; i + dev->txpos + 1 < dev->txlen; i++) {
if (needs_escape(dev->txbuf[dev->txpos + i + 1]))
break;
}
return i;
}
static int write_chunk(struct mctp_serial *dev, unsigned char *buf, int len)
{
return dev->tty->ops->write(dev->tty, buf, len);
}
static void mctp_serial_tx_work(struct work_struct *work)
{
struct mctp_serial *dev = container_of(work, struct mctp_serial,
tx_work);
unsigned char c, buf[3];
unsigned long flags;
int len, txlen;
spin_lock_irqsave(&dev->lock, flags);
/* txstate represents the next thing to send */
switch (dev->txstate) {
case STATE_START:
dev->txpos = 0;
fallthrough;
case STATE_HEADER:
buf[0] = BYTE_FRAME;
buf[1] = MCTP_SERIAL_VERSION;
buf[2] = dev->txlen;
if (!dev->txpos)
dev->txfcs = crc_ccitt(0, buf + 1, 2);
txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
if (txlen <= 0) {
dev->txstate = STATE_ERR;
} else {
dev->txpos += txlen;
if (dev->txpos == 3) {
dev->txstate = STATE_DATA;
dev->txpos = 0;
}
}
break;
case STATE_ESCAPE:
buf[0] = dev->txbuf[dev->txpos] & ~0x20;
txlen = write_chunk(dev, buf, 1);
if (txlen <= 0) {
dev->txstate = STATE_ERR;
} else {
dev->txpos += txlen;
if (dev->txpos == dev->txlen) {
dev->txstate = STATE_TRAILER;
dev->txpos = 0;
}
}
break;
case STATE_DATA:
len = next_chunk_len(dev);
if (len) {
c = dev->txbuf[dev->txpos];
if (len == 1 && needs_escape(c)) {
buf[0] = BYTE_ESC;
buf[1] = c & ~0x20;
dev->txfcs = crc_ccitt_byte(dev->txfcs, c);
txlen = write_chunk(dev, buf, 2);
if (txlen == 2)
dev->txpos++;
else if (txlen == 1)
dev->txstate = STATE_ESCAPE;
else
dev->txstate = STATE_ERR;
} else {
txlen = write_chunk(dev,
dev->txbuf + dev->txpos,
len);
if (txlen <= 0) {
dev->txstate = STATE_ERR;
} else {
dev->txfcs = crc_ccitt(dev->txfcs,
dev->txbuf +
dev->txpos,
txlen);
dev->txpos += txlen;
}
}
if (dev->txstate == STATE_DATA &&
dev->txpos == dev->txlen) {
dev->txstate = STATE_TRAILER;
dev->txpos = 0;
}
break;
}
dev->txstate = STATE_TRAILER;
dev->txpos = 0;
fallthrough;
case STATE_TRAILER:
buf[0] = dev->txfcs >> 8;
buf[1] = dev->txfcs & 0xff;
buf[2] = BYTE_FRAME;
txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
if (txlen <= 0) {
dev->txstate = STATE_ERR;
} else {
dev->txpos += txlen;
if (dev->txpos == 3) {
dev->txstate = STATE_DONE;
dev->txpos = 0;
}
}
break;
default:
netdev_err_once(dev->netdev, "invalid tx state %d\n",
dev->txstate);
}
if (dev->txstate == STATE_DONE) {
dev->netdev->stats.tx_packets++;
dev->netdev->stats.tx_bytes += dev->txlen;
dev->txlen = 0;
dev->txpos = 0;
clear_bit(TTY_DO_WRITE_WAKEUP, &dev->tty->flags);
dev->txstate = STATE_IDLE;
spin_unlock_irqrestore(&dev->lock, flags);
netif_wake_queue(dev->netdev);
} else {
spin_unlock_irqrestore(&dev->lock, flags);
}
}
static netdev_tx_t mctp_serial_tx(struct sk_buff *skb, struct net_device *ndev)
{
struct mctp_serial *dev = netdev_priv(ndev);
unsigned long flags;
WARN_ON(dev->txstate != STATE_IDLE);
if (skb->len > MCTP_SERIAL_MTU) {
dev->netdev->stats.tx_dropped++;
goto out;
}
spin_lock_irqsave(&dev->lock, flags);
netif_stop_queue(dev->netdev);
skb_copy_bits(skb, 0, dev->txbuf, skb->len);
dev->txpos = 0;
dev->txlen = skb->len;
dev->txstate = STATE_START;
spin_unlock_irqrestore(&dev->lock, flags);
set_bit(TTY_DO_WRITE_WAKEUP, &dev->tty->flags);
schedule_work(&dev->tx_work);
out:
kfree_skb(skb);
return NETDEV_TX_OK;
}
static void mctp_serial_tty_write_wakeup(struct tty_struct *tty)
{
struct mctp_serial *dev = tty->disc_data;
schedule_work(&dev->tx_work);
}
static void mctp_serial_rx(struct mctp_serial *dev)
{
struct mctp_skb_cb *cb;
struct sk_buff *skb;
if (dev->rxfcs != dev->rxfcs_rcvd) {
dev->netdev->stats.rx_dropped++;
dev->netdev->stats.rx_crc_errors++;
return;
}
skb = netdev_alloc_skb(dev->netdev, dev->rxlen);
if (!skb) {
dev->netdev->stats.rx_dropped++;
return;
}
skb->protocol = htons(ETH_P_MCTP);
skb_put_data(skb, dev->rxbuf, dev->rxlen);
skb_reset_network_header(skb);
cb = __mctp_cb(skb);
cb->halen = 0;
netif_rx_ni(skb);
dev->netdev->stats.rx_packets++;
dev->netdev->stats.rx_bytes += dev->rxlen;
}
static void mctp_serial_push_header(struct mctp_serial *dev, unsigned char c)
{
switch (dev->rxpos) {
case 0:
if (c == BYTE_FRAME)
dev->rxpos++;
else
dev->rxstate = STATE_ERR;
break;
case 1:
if (c == MCTP_SERIAL_VERSION) {
dev->rxpos++;
dev->rxfcs = crc_ccitt_byte(0, c);
} else {
dev->rxstate = STATE_ERR;
}
break;
case 2:
if (c > MCTP_SERIAL_FRAME_MTU) {
dev->rxstate = STATE_ERR;
} else {
dev->rxlen = c;
dev->rxpos = 0;
dev->rxstate = STATE_DATA;
dev->rxfcs = crc_ccitt_byte(dev->rxfcs, c);
}
break;
}
}
static void mctp_serial_push_trailer(struct mctp_serial *dev, unsigned char c)
{
switch (dev->rxpos) {
case 0:
dev->rxfcs_rcvd = c << 8;
dev->rxpos++;
break;
case 1:
dev->rxfcs_rcvd |= c;
dev->rxpos++;
break;
case 2:
if (c != BYTE_FRAME) {
dev->rxstate = STATE_ERR;
} else {
mctp_serial_rx(dev);
dev->rxlen = 0;
dev->rxpos = 0;
dev->rxstate = STATE_IDLE;
}
break;
}
}
static void mctp_serial_push(struct mctp_serial *dev, unsigned char c)
{
switch (dev->rxstate) {
case STATE_IDLE:
dev->rxstate = STATE_HEADER;
fallthrough;
case STATE_HEADER:
mctp_serial_push_header(dev, c);
break;
case STATE_ESCAPE:
c |= 0x20;
fallthrough;
case STATE_DATA:
if (dev->rxstate != STATE_ESCAPE && c == BYTE_ESC) {
dev->rxstate = STATE_ESCAPE;
} else {
dev->rxfcs = crc_ccitt_byte(dev->rxfcs, c);
dev->rxbuf[dev->rxpos] = c;
dev->rxpos++;
dev->rxstate = STATE_DATA;
if (dev->rxpos == dev->rxlen) {
dev->rxpos = 0;
dev->rxstate = STATE_TRAILER;
}
}
break;
case STATE_TRAILER:
mctp_serial_push_trailer(dev, c);
break;
case STATE_ERR:
if (c == BYTE_FRAME)
dev->rxstate = STATE_IDLE;
break;
default:
netdev_err_once(dev->netdev, "invalid rx state %d\n",
dev->rxstate);
}
}
static void mctp_serial_tty_receive_buf(struct tty_struct *tty,
const unsigned char *c,
const char *f, int len)
{
struct mctp_serial *dev = tty->disc_data;
int i;
if (!netif_running(dev->netdev))
return;
/* we don't (currently) use the flag bytes, just data. */
for (i = 0; i < len; i++)
mctp_serial_push(dev, c[i]);
}
static const struct net_device_ops mctp_serial_netdev_ops = {
.ndo_start_xmit = mctp_serial_tx,
};
static void mctp_serial_setup(struct net_device *ndev)
{
ndev->type = ARPHRD_MCTP;
/* we limit at the fixed MTU, which is also the MCTP-standard
* baseline MTU, so is also our minimum
*/
ndev->mtu = MCTP_SERIAL_MTU;
ndev->max_mtu = MCTP_SERIAL_MTU;
ndev->min_mtu = MCTP_SERIAL_MTU;
ndev->hard_header_len = 0;
ndev->addr_len = 0;
ndev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
ndev->flags = IFF_NOARP;
ndev->netdev_ops = &mctp_serial_netdev_ops;
ndev->needs_free_netdev = true;
}
static int mctp_serial_open(struct tty_struct *tty)
{
struct mctp_serial *dev;
struct net_device *ndev;
char name[32];
int idx, rc;
if (!capable(CAP_NET_ADMIN))
return -EPERM;
if (!tty->ops->write)
return -EOPNOTSUPP;
idx = ida_alloc(&mctp_serial_ida, GFP_KERNEL);
if (idx < 0)
return idx;
snprintf(name, sizeof(name), "mctpserial%d", idx);
ndev = alloc_netdev(sizeof(*dev), name, NET_NAME_ENUM,
mctp_serial_setup);
if (!ndev) {
rc = -ENOMEM;
goto free_ida;
}
dev = netdev_priv(ndev);
dev->idx = idx;
dev->tty = tty;
dev->netdev = ndev;
dev->txstate = STATE_IDLE;
dev->rxstate = STATE_IDLE;
spin_lock_init(&dev->lock);
INIT_WORK(&dev->tx_work, mctp_serial_tx_work);
rc = register_netdev(ndev);
if (rc)
goto free_netdev;
tty->receive_room = 64 * 1024;
tty->disc_data = dev;
return 0;
free_netdev:
free_netdev(ndev);
free_ida:
ida_free(&mctp_serial_ida, idx);
return rc;
}
static void mctp_serial_close(struct tty_struct *tty)
{
struct mctp_serial *dev = tty->disc_data;
int idx = dev->idx;
unregister_netdev(dev->netdev);
cancel_work_sync(&dev->tx_work);
ida_free(&mctp_serial_ida, idx);
}
static struct tty_ldisc_ops mctp_ldisc = {
.owner = THIS_MODULE,
.num = N_MCTP,
.name = "mctp",
.open = mctp_serial_open,
.close = mctp_serial_close,
.receive_buf = mctp_serial_tty_receive_buf,
.write_wakeup = mctp_serial_tty_write_wakeup,
};
static int __init mctp_serial_init(void)
{
return tty_register_ldisc(&mctp_ldisc);
}
static void __exit mctp_serial_exit(void)
{
tty_unregister_ldisc(&mctp_ldisc);
}
module_init(mctp_serial_init);
module_exit(mctp_serial_exit);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Jeremy Kerr <jk@codeconstruct.com.au>");
MODULE_DESCRIPTION("MCTP Serial transport");