net/sched/sch_taprio.c

// SPDX-License-Identifier: GPL-2.0

/* net/sched/sch_taprio.c	 Time Aware Priority Scheduler
 *
 * Authors:	Vinicius Costa Gomes <vinicius.gomes@intel.com>
 *
 */

#include <linux/ethtool.h>
#include <linux/ethtool_netlink.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/math64.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/time.h>
#include <net/gso.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>
#include <net/pkt_cls.h>
#include <net/sch_generic.h>
#include <net/sock.h>
#include <net/tcp.h>

#define TAPRIO_STAT_NOT_SET	(~0ULL)

#include "sch_mqprio_lib.h"

static LIST_HEAD(taprio_list);
static struct static_key_false taprio_have_broken_mqprio;
static struct static_key_false taprio_have_working_mqprio;

#define TAPRIO_ALL_GATES_OPEN -1

#define TXTIME_ASSIST_IS_ENABLED(flags) ((flags) & TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST)
#define FULL_OFFLOAD_IS_ENABLED(flags) ((flags) & TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
#define TAPRIO_SUPPORTED_FLAGS \
	(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
#define TAPRIO_FLAGS_INVALID U32_MAX
/* Minimum value for picos_per_byte to ensure non-zero duration
 * for minimum-sized Ethernet frames (ETH_ZLEN = 60).
 * 60 * 17 > PSEC_PER_NSEC (1000)
 */
#define TAPRIO_PICOS_PER_BYTE_MIN 17

struct sched_entry {
	/* Durations between this GCL entry and the GCL entry where the
	 * respective traffic class gate closes
	 */
	u64 gate_duration[TC_MAX_QUEUE];
	atomic_t budget[TC_MAX_QUEUE];
	/* The qdisc makes some effort so that no packet leaves
	 * after this time
	 */
	ktime_t gate_close_time[TC_MAX_QUEUE];
	struct list_head list;
	/* Used to calculate when to advance the schedule */
	ktime_t end_time;
	ktime_t next_txtime;
	int index;
	u32 gate_mask;
	u32 interval;
	u8 command;
};

struct sched_gate_list {
	/* Longest non-zero contiguous gate durations per traffic class,
	 * or 0 if a traffic class gate never opens during the schedule.
	 */
	u64 max_open_gate_duration[TC_MAX_QUEUE];
	u32 max_frm_len[TC_MAX_QUEUE]; /* for the fast path */
	u32 max_sdu[TC_MAX_QUEUE]; /* for dump */
	struct rcu_head rcu;
	struct list_head entries;
	size_t num_entries;
	ktime_t cycle_end_time;
	s64 cycle_time;
	s64 cycle_time_extension;
	s64 base_time;
};

struct taprio_sched {
	struct Qdisc **qdiscs;
	struct Qdisc *root;
	u32 flags;
	enum tk_offsets tk_offset;
	int clockid;
	bool offloaded;
	bool detected_mqprio;
	bool broken_mqprio;
	atomic64_t picos_per_byte; /* Using picoseconds because for 10Gbps+
				    * speeds it's sub-nanoseconds per byte
				    */

	/* Protects the update side of the RCU protected current_entry */
	spinlock_t current_entry_lock;
	struct sched_entry __rcu *current_entry;
	struct sched_gate_list __rcu *oper_sched;
	struct sched_gate_list __rcu *admin_sched;
	struct hrtimer advance_timer;
	struct list_head taprio_list;
	int cur_txq[TC_MAX_QUEUE];
	u32 max_sdu[TC_MAX_QUEUE]; /* save info from the user */
	u32 fp[TC_QOPT_MAX_QUEUE]; /* only for dump and offloading */
	u32 txtime_delay;
};

struct __tc_taprio_qopt_offload {
	refcount_t users;
	struct tc_taprio_qopt_offload offload;
};

static void taprio_calculate_gate_durations(struct taprio_sched *q,
					    struct sched_gate_list *sched)
{
	struct net_device *dev = qdisc_dev(q->root);
	int num_tc = netdev_get_num_tc(dev);
	struct sched_entry *entry, *cur;
	int tc;

	list_for_each_entry(entry, &sched->entries, list) {
		u32 gates_still_open = entry->gate_mask;

		/* For each traffic class, calculate each open gate duration,
		 * starting at this schedule entry and ending at the schedule
		 * entry containing a gate close event for that TC.
		 */
		cur = entry;

		do {
			if (!gates_still_open)
				break;

			for (tc = 0; tc < num_tc; tc++) {
				if (!(gates_still_open & BIT(tc)))
					continue;

				if (cur->gate_mask & BIT(tc))
					entry->gate_duration[tc] += cur->interval;
				else
					gates_still_open &= ~BIT(tc);
			}

			cur = list_next_entry_circular(cur, &sched->entries, list);
		} while (cur != entry);

		/* Keep track of the maximum gate duration for each traffic
		 * class, taking care to not confuse a traffic class which is
		 * temporarily closed with one that is always closed.
		 */
		for (tc = 0; tc < num_tc; tc++)
			if (entry->gate_duration[tc] &&
			    sched->max_open_gate_duration[tc] < entry->gate_duration[tc])
				sched->max_open_gate_duration[tc] = entry->gate_duration[tc];
	}
}

static bool taprio_entry_allows_tx(ktime_t skb_end_time,
				   struct sched_entry *entry, int tc)
{
	return ktime_before(skb_end_time, entry->gate_close_time[tc]);
}

static ktime_t sched_base_time(const struct sched_gate_list *sched)
{
	if (!sched)
		return KTIME_MAX;

	return ns_to_ktime(sched->base_time);
}

static ktime_t taprio_mono_to_any(const struct taprio_sched *q, ktime_t mono)
{
	/* This pairs with WRITE_ONCE() in taprio_parse_clockid() */
	enum tk_offsets tk_offset = READ_ONCE(q->tk_offset);

	switch (tk_offset) {
	case TK_OFFS_MAX:
		return mono;
	default:
		return ktime_mono_to_any(mono, tk_offset);
	}
}

static ktime_t taprio_get_time(const struct taprio_sched *q)
{
	return taprio_mono_to_any(q, ktime_get());
}

static void taprio_free_sched_cb(struct rcu_head *head)
{
	struct sched_gate_list *sched = container_of(head, struct sched_gate_list, rcu);
	struct sched_entry *entry, *n;

	list_for_each_entry_safe(entry, n, &sched->entries, list) {
		list_del(&entry->list);
		kfree(entry);
	}

	kfree(sched);
}

static void switch_schedules(struct taprio_sched *q,
			     struct sched_gate_list **admin,
			     struct sched_gate_list **oper)
{
	rcu_assign_pointer(q->oper_sched, *admin);
	rcu_assign_pointer(q->admin_sched, NULL);

	if (*oper)
		call_rcu(&(*oper)->rcu, taprio_free_sched_cb);

	*oper = *admin;
	*admin = NULL;
}

/* Get how much time has been already elapsed in the current cycle. */
static s32 get_cycle_time_elapsed(struct sched_gate_list *sched, ktime_t time)
{
	ktime_t time_since_sched_start;
	s32 time_elapsed;

	time_since_sched_start = ktime_sub(time, sched->base_time);
	div_s64_rem(time_since_sched_start, sched->cycle_time, &time_elapsed);

	return time_elapsed;
}

static ktime_t get_interval_end_time(struct sched_gate_list *sched,
				     struct sched_gate_list *admin,
				     struct sched_entry *entry,
				     ktime_t intv_start)
{
	s32 cycle_elapsed = get_cycle_time_elapsed(sched, intv_start);
	ktime_t intv_end, cycle_ext_end, cycle_end;

	cycle_end = ktime_add_ns(intv_start, sched->cycle_time - cycle_elapsed);
	intv_end = ktime_add_ns(intv_start, entry->interval);
	cycle_ext_end = ktime_add(cycle_end, sched->cycle_time_extension);

	if (ktime_before(intv_end, cycle_end))
		return intv_end;
	else if (admin && admin != sched &&
		 ktime_after(admin->base_time, cycle_end) &&
		 ktime_before(admin->base_time, cycle_ext_end))
		return admin->base_time;
	else
		return cycle_end;
}

static int length_to_duration(struct taprio_sched *q, int len)
{
	return div_u64(len * atomic64_read(&q->picos_per_byte), PSEC_PER_NSEC);
}

static int duration_to_length(struct taprio_sched *q, u64 duration)
{
	return div_u64(duration * PSEC_PER_NSEC, atomic64_read(&q->picos_per_byte));
}

/* Sets sched->max_sdu[] and sched->max_frm_len[] to the minimum between the
 * q->max_sdu[] requested by the user and the max_sdu dynamically determined by
 * the maximum open gate durations at the given link speed.
 */
static void taprio_update_queue_max_sdu(struct taprio_sched *q,
					struct sched_gate_list *sched,
					struct qdisc_size_table *stab)
{
	struct net_device *dev = qdisc_dev(q->root);
	int num_tc = netdev_get_num_tc(dev);
	u32 max_sdu_from_user;
	u32 max_sdu_dynamic;
	u32 max_sdu;
	int tc;

	for (tc = 0; tc < num_tc; tc++) {
		max_sdu_from_user = q->max_sdu[tc] ?: U32_MAX;

		/* TC gate never closes => keep the queueMaxSDU
		 * selected by the user
		 */
		if (sched->max_open_gate_duration[tc] == sched->cycle_time) {
			max_sdu_dynamic = U32_MAX;
		} else {
			u32 max_frm_len;

			max_frm_len = duration_to_length(q, sched->max_open_gate_duration[tc]);
			/* Compensate for L1 overhead from size table,
			 * but don't let the frame size go negative
			 */
			if (stab) {
				max_frm_len -= stab->szopts.overhead;
				max_frm_len = max_t(int, max_frm_len,
						    dev->hard_header_len + 1);
			}
			max_sdu_dynamic = max_frm_len - dev->hard_header_len;
			if (max_sdu_dynamic > dev->max_mtu)
				max_sdu_dynamic = U32_MAX;
		}

		max_sdu = min(max_sdu_dynamic, max_sdu_from_user);

		if (max_sdu != U32_MAX) {
			sched->max_frm_len[tc] = max_sdu + dev->hard_header_len;
			WRITE_ONCE(sched->max_sdu[tc], max_sdu);
		} else {
			sched->max_frm_len[tc] = U32_MAX; /* never oversized */
			WRITE_ONCE(sched->max_sdu[tc], 0);
		}
	}
}

/* Returns the entry corresponding to next available interval. If
 * validate_interval is set, it only validates whether the timestamp occurs
 * when the gate corresponding to the skb's traffic class is open.
 */
static struct sched_entry *find_entry_to_transmit(struct sk_buff *skb,
						  struct Qdisc *sch,
						  struct sched_gate_list *sched,
						  struct sched_gate_list *admin,
						  ktime_t time,
						  ktime_t *interval_start,
						  ktime_t *interval_end,
						  bool validate_interval)
{
	ktime_t curr_intv_start, curr_intv_end, cycle_end, packet_transmit_time;
	ktime_t earliest_txtime = KTIME_MAX, txtime, cycle, transmit_end_time;
	struct sched_entry *entry = NULL, *entry_found = NULL;
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	bool entry_available = false;
	s32 cycle_elapsed;
	int tc, n;

	tc = netdev_get_prio_tc_map(dev, skb->priority);
	packet_transmit_time = length_to_duration(q, qdisc_pkt_len(skb));

	*interval_start = 0;
	*interval_end = 0;

	if (!sched)
		return NULL;

	cycle = sched->cycle_time;
	cycle_elapsed = get_cycle_time_elapsed(sched, time);
	curr_intv_end = ktime_sub_ns(time, cycle_elapsed);
	cycle_end = ktime_add_ns(curr_intv_end, cycle);

	list_for_each_entry(entry, &sched->entries, list) {
		curr_intv_start = curr_intv_end;
		curr_intv_end = get_interval_end_time(sched, admin, entry,
						      curr_intv_start);

		if (ktime_after(curr_intv_start, cycle_end))
			break;

		if (!(entry->gate_mask & BIT(tc)) ||
		    packet_transmit_time > entry->interval)
			continue;

		txtime = entry->next_txtime;

		if (ktime_before(txtime, time) || validate_interval) {
			transmit_end_time = ktime_add_ns(time, packet_transmit_time);
			if ((ktime_before(curr_intv_start, time) &&
			     ktime_before(transmit_end_time, curr_intv_end)) ||
			    (ktime_after(curr_intv_start, time) && !validate_interval)) {
				entry_found = entry;
				*interval_start = curr_intv_start;
				*interval_end = curr_intv_end;
				break;
			} else if (!entry_available && !validate_interval) {
				/* Here, we are just trying to find out the
				 * first available interval in the next cycle.
				 */
				entry_available = true;
				entry_found = entry;
				*interval_start = ktime_add_ns(curr_intv_start, cycle);
				*interval_end = ktime_add_ns(curr_intv_end, cycle);
			}
		} else if (ktime_before(txtime, earliest_txtime) &&
			   !entry_available) {
			earliest_txtime = txtime;
			entry_found = entry;
			n = div_s64(ktime_sub(txtime, curr_intv_start), cycle);
			*interval_start = ktime_add(curr_intv_start, n * cycle);
			*interval_end = ktime_add(curr_intv_end, n * cycle);
		}
	}

	return entry_found;
}

static bool is_valid_interval(struct sk_buff *skb, struct Qdisc *sch)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct sched_gate_list *sched, *admin;
	ktime_t interval_start, interval_end;
	struct sched_entry *entry;

	rcu_read_lock();
	sched = rcu_dereference(q->oper_sched);
	admin = rcu_dereference(q->admin_sched);

	entry = find_entry_to_transmit(skb, sch, sched, admin, skb->tstamp,
				       &interval_start, &interval_end, true);
	rcu_read_unlock();

	return entry;
}

/* This returns the tstamp value set by TCP in terms of the set clock. */
static ktime_t get_tcp_tstamp(struct taprio_sched *q, struct sk_buff *skb)
{
	unsigned int offset = skb_network_offset(skb);
	const struct ipv6hdr *ipv6h;
	const struct iphdr *iph;
	struct ipv6hdr _ipv6h;

	ipv6h = skb_header_pointer(skb, offset, sizeof(_ipv6h), &_ipv6h);
	if (!ipv6h)
		return 0;

	if (ipv6h->version == 4) {
		iph = (struct iphdr *)ipv6h;
		offset += iph->ihl * 4;

		/* special-case 6in4 tunnelling, as that is a common way to get
		 * v6 connectivity in the home
		 */
		if (iph->protocol == IPPROTO_IPV6) {
			ipv6h = skb_header_pointer(skb, offset,
						   sizeof(_ipv6h), &_ipv6h);

			if (!ipv6h || ipv6h->nexthdr != IPPROTO_TCP)
				return 0;
		} else if (iph->protocol != IPPROTO_TCP) {
			return 0;
		}
	} else if (ipv6h->version == 6 && ipv6h->nexthdr != IPPROTO_TCP) {
		return 0;
	}

	return taprio_mono_to_any(q, skb->skb_mstamp_ns);
}

/* There are a few scenarios where we will have to modify the txtime from
 * what is read from next_txtime in sched_entry. They are:
 * 1. If txtime is in the past,
 *    a. The gate for the traffic class is currently open and packet can be
 *       transmitted before it closes, schedule the packet right away.
 *    b. If the gate corresponding to the traffic class is going to open later
 *       in the cycle, set the txtime of packet to the interval start.
 * 2. If txtime is in the future, there are packets corresponding to the
 *    current traffic class waiting to be transmitted. So, the following
 *    possibilities exist:
 *    a. We can transmit the packet before the window containing the txtime
 *       closes.
 *    b. The window might close before the transmission can be completed
 *       successfully. So, schedule the packet in the next open window.
 */
static long get_packet_txtime(struct sk_buff *skb, struct Qdisc *sch)
{
	ktime_t transmit_end_time, interval_end, interval_start, tcp_tstamp;
	struct taprio_sched *q = qdisc_priv(sch);
	struct sched_gate_list *sched, *admin;
	ktime_t minimum_time, now, txtime;
	int len, packet_transmit_time;
	struct sched_entry *entry;
	bool sched_changed;

	now = taprio_get_time(q);
	minimum_time = ktime_add_ns(now, q->txtime_delay);

	tcp_tstamp = get_tcp_tstamp(q, skb);
	minimum_time = max_t(ktime_t, minimum_time, tcp_tstamp);

	rcu_read_lock();
	admin = rcu_dereference(q->admin_sched);
	sched = rcu_dereference(q->oper_sched);
	if (admin && ktime_after(minimum_time, admin->base_time))
		switch_schedules(q, &admin, &sched);

	/* Until the schedule starts, all the queues are open */
	if (!sched || ktime_before(minimum_time, sched->base_time)) {
		txtime = minimum_time;
		goto done;
	}

	len = qdisc_pkt_len(skb);
	packet_transmit_time = length_to_duration(q, len);

	do {
		sched_changed = false;

		entry = find_entry_to_transmit(skb, sch, sched, admin,
					       minimum_time,
					       &interval_start, &interval_end,
					       false);
		if (!entry) {
			txtime = 0;
			goto done;
		}

		txtime = entry->next_txtime;
		txtime = max_t(ktime_t, txtime, minimum_time);
		txtime = max_t(ktime_t, txtime, interval_start);

		if (admin && admin != sched &&
		    ktime_after(txtime, admin->base_time)) {
			sched = admin;
			sched_changed = true;
			continue;
		}

		transmit_end_time = ktime_add(txtime, packet_transmit_time);
		minimum_time = transmit_end_time;

		/* Update the txtime of current entry to the next time it's
		 * interval starts.
		 */
		if (ktime_after(transmit_end_time, interval_end))
			entry->next_txtime = ktime_add(interval_start, sched->cycle_time);
	} while (sched_changed || ktime_after(transmit_end_time, interval_end));

	entry->next_txtime = transmit_end_time;

done:
	rcu_read_unlock();
	return txtime;
}

/* Devices with full offload are expected to honor this in hardware */
static bool taprio_skb_exceeds_queue_max_sdu(struct Qdisc *sch,
					     struct sk_buff *skb)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	struct sched_gate_list *sched;
	int prio = skb->priority;
	bool exceeds = false;
	u8 tc;

	tc = netdev_get_prio_tc_map(dev, prio);

	rcu_read_lock();
	sched = rcu_dereference(q->oper_sched);
	if (sched && skb->len > sched->max_frm_len[tc])
		exceeds = true;
	rcu_read_unlock();

	return exceeds;
}

static int taprio_enqueue_one(struct sk_buff *skb, struct Qdisc *sch,
			      struct Qdisc *child, struct sk_buff **to_free)
{
	struct taprio_sched *q = qdisc_priv(sch);

	/* sk_flags are only safe to use on full sockets. */
	if (skb->sk && sk_fullsock(skb->sk) && sock_flag(skb->sk, SOCK_TXTIME)) {
		if (!is_valid_interval(skb, sch))
			return qdisc_drop(skb, sch, to_free);
	} else if (TXTIME_ASSIST_IS_ENABLED(q->flags)) {
		skb->tstamp = get_packet_txtime(skb, sch);
		if (!skb->tstamp)
			return qdisc_drop(skb, sch, to_free);
	}

	qdisc_qstats_backlog_inc(sch, skb);
	qdisc_qlen_inc(sch);

	return qdisc_enqueue(skb, child, to_free);
}

static int taprio_enqueue_segmented(struct sk_buff *skb, struct Qdisc *sch,
				    struct Qdisc *child,
				    struct sk_buff **to_free)
{
	unsigned int slen = 0, numsegs = 0, len = qdisc_pkt_len(skb);
	netdev_features_t features = netif_skb_features(skb);
	struct sk_buff *segs, *nskb;
	int ret;

	segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
	if (IS_ERR_OR_NULL(segs))
		return qdisc_drop(skb, sch, to_free);

	skb_list_walk_safe(segs, segs, nskb) {
		skb_mark_not_on_list(segs);
		qdisc_skb_cb(segs)->pkt_len = segs->len;
		qdisc_skb_cb(segs)->pkt_segs = 1;
		slen += segs->len;

		/* FIXME: we should be segmenting to a smaller size
		 * rather than dropping these
		 */
		if (taprio_skb_exceeds_queue_max_sdu(sch, segs))
			ret = qdisc_drop(segs, sch, to_free);
		else
			ret = taprio_enqueue_one(segs, sch, child, to_free);

		if (ret != NET_XMIT_SUCCESS) {
			if (net_xmit_drop_count(ret))
				qdisc_qstats_drop(sch);
		} else {
			numsegs++;
		}
	}

	if (numsegs > 1)
		qdisc_tree_reduce_backlog(sch, 1 - numsegs, len - slen);
	consume_skb(skb);

	return numsegs > 0 ? NET_XMIT_SUCCESS : NET_XMIT_DROP;
}

/* Will not be called in the full offload case, since the TX queues are
 * attached to the Qdisc created using qdisc_create_dflt()
 */
static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
			  struct sk_buff **to_free)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct Qdisc *child;
	int queue;

	queue = skb_get_queue_mapping(skb);

	child = q->qdiscs[queue];
	if (unlikely(child == &noop_qdisc))
		return qdisc_drop(skb, sch, to_free);

	if (taprio_skb_exceeds_queue_max_sdu(sch, skb)) {
		/* Large packets might not be transmitted when the transmission
		 * duration exceeds any configured interval. Therefore, segment
		 * the skb into smaller chunks. Drivers with full offload are
		 * expected to handle this in hardware.
		 */
		if (skb_is_gso(skb))
			return taprio_enqueue_segmented(skb, sch, child,
							to_free);

		return qdisc_drop(skb, sch, to_free);
	}

	return taprio_enqueue_one(skb, sch, child, to_free);
}

static struct sk_buff *taprio_peek(struct Qdisc *sch)
{
	WARN_ONCE(1, "taprio only supports operating as root qdisc, peek() not implemented");
	return NULL;
}

static void taprio_set_budgets(struct taprio_sched *q,
			       struct sched_gate_list *sched,
			       struct sched_entry *entry)
{
	struct net_device *dev = qdisc_dev(q->root);
	int num_tc = netdev_get_num_tc(dev);
	int tc, budget;

	for (tc = 0; tc < num_tc; tc++) {
		/* Traffic classes which never close have infinite budget */
		if (entry->gate_duration[tc] == sched->cycle_time)
			budget = INT_MAX;
		else
			budget = div64_u64((u64)entry->gate_duration[tc] * PSEC_PER_NSEC,
					   atomic64_read(&q->picos_per_byte));

		atomic_set(&entry->budget[tc], budget);
	}
}

/* When an skb is sent, it consumes from the budget of all traffic classes */
static int taprio_update_budgets(struct sched_entry *entry, size_t len,
				 int tc_consumed, int num_tc)
{
	int tc, budget, new_budget = 0;

	for (tc = 0; tc < num_tc; tc++) {
		budget = atomic_read(&entry->budget[tc]);
		/* Don't consume from infinite budget */
		if (budget == INT_MAX) {
			if (tc == tc_consumed)
				new_budget = budget;
			continue;
		}

		if (tc == tc_consumed)
			new_budget = atomic_sub_return(len, &entry->budget[tc]);
		else
			atomic_sub(len, &entry->budget[tc]);
	}

	return new_budget;
}

static struct sk_buff *taprio_dequeue_from_txq(struct Qdisc *sch, int txq,
					       struct sched_entry *entry,
					       u32 gate_mask)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	struct Qdisc *child = q->qdiscs[txq];
	int num_tc = netdev_get_num_tc(dev);
	struct sk_buff *skb;
	ktime_t guard;
	int prio;
	int len;
	u8 tc;

	if (unlikely(child == &noop_qdisc))
		return NULL;

	if (TXTIME_ASSIST_IS_ENABLED(q->flags))
		goto skip_peek_checks;

	skb = child->ops->peek(child);
	if (!skb)
		return NULL;

	prio = skb->priority;
	tc = netdev_get_prio_tc_map(dev, prio);

	if (!(gate_mask & BIT(tc)))
		return NULL;

	len = qdisc_pkt_len(skb);
	guard = ktime_add_ns(taprio_get_time(q), length_to_duration(q, len));

	/* In the case that there's no gate entry, there's no
	 * guard band ...
	 */
	if (gate_mask != TAPRIO_ALL_GATES_OPEN &&
	    !taprio_entry_allows_tx(guard, entry, tc))
		return NULL;

	/* ... and no budget. */
	if (gate_mask != TAPRIO_ALL_GATES_OPEN &&
	    taprio_update_budgets(entry, len, tc, num_tc) < 0)
		return NULL;

skip_peek_checks:
	skb = qdisc_dequeue_peeked(child);
	if (unlikely(!skb))
		return NULL;

	qdisc_bstats_update(sch, skb);
	qdisc_qstats_backlog_dec(sch, skb);
	qdisc_qlen_dec(sch);

	return skb;
}

static void taprio_next_tc_txq(struct net_device *dev, int tc, int *txq)
{
	int offset = dev->tc_to_txq[tc].offset;
	int count = dev->tc_to_txq[tc].count;

	(*txq)++;
	if (*txq == offset + count)
		*txq = offset;
}

/* Prioritize higher traffic classes, and select among TXQs belonging to the
 * same TC using round robin
 */
static struct sk_buff *taprio_dequeue_tc_priority(struct Qdisc *sch,
						  struct sched_entry *entry,
						  u32 gate_mask)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	int num_tc = netdev_get_num_tc(dev);
	struct sk_buff *skb;
	int tc;

	for (tc = num_tc - 1; tc >= 0; tc--) {
		int first_txq = q->cur_txq[tc];

		if (!(gate_mask & BIT(tc)))
			continue;

		do {
			skb = taprio_dequeue_from_txq(sch, q->cur_txq[tc],
						      entry, gate_mask);

			taprio_next_tc_txq(dev, tc, &q->cur_txq[tc]);

			if (q->cur_txq[tc] >= dev->num_tx_queues)
				q->cur_txq[tc] = first_txq;

			if (skb)
				return skb;
		} while (q->cur_txq[tc] != first_txq);
	}

	return NULL;
}

/* Broken way of prioritizing smaller TXQ indices and ignoring the traffic
 * class other than to determine whether the gate is open or not
 */
static struct sk_buff *taprio_dequeue_txq_priority(struct Qdisc *sch,
						   struct sched_entry *entry,
						   u32 gate_mask)
{
	struct net_device *dev = qdisc_dev(sch);
	struct sk_buff *skb;
	int i;

	for (i = 0; i < dev->num_tx_queues; i++) {
		skb = taprio_dequeue_from_txq(sch, i, entry, gate_mask);
		if (skb)
			return skb;
	}

	return NULL;
}

/* Will not be called in the full offload case, since the TX queues are
 * attached to the Qdisc created using qdisc_create_dflt()
 */
static struct sk_buff *taprio_dequeue(struct Qdisc *sch)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct sk_buff *skb = NULL;
	struct sched_entry *entry;
	u32 gate_mask;

	rcu_read_lock();
	entry = rcu_dereference(q->current_entry);
	/* if there's no entry, it means that the schedule didn't
	 * start yet, so force all gates to be open, this is in
	 * accordance to IEEE 802.1Qbv-2015 Section 8.6.9.4.5
	 * "AdminGateStates"
	 */
	gate_mask = entry ? entry->gate_mask : TAPRIO_ALL_GATES_OPEN;
	if (!gate_mask)
		goto done;

	if (static_branch_unlikely(&taprio_have_broken_mqprio) &&
	    !static_branch_likely(&taprio_have_working_mqprio)) {
		/* Single NIC kind which is broken */
		skb = taprio_dequeue_txq_priority(sch, entry, gate_mask);
	} else if (static_branch_likely(&taprio_have_working_mqprio) &&
		   !static_branch_unlikely(&taprio_have_broken_mqprio)) {
		/* Single NIC kind which prioritizes properly */
		skb = taprio_dequeue_tc_priority(sch, entry, gate_mask);
	} else {
		/* Mixed NIC kinds present in system, need dynamic testing */
		if (q->broken_mqprio)
			skb = taprio_dequeue_txq_priority(sch, entry, gate_mask);
		else
			skb = taprio_dequeue_tc_priority(sch, entry, gate_mask);
	}

done:
	rcu_read_unlock();

	return skb;
}

static bool should_restart_cycle(const struct sched_gate_list *oper,
				 const struct sched_entry *entry)
{
	if (list_is_last(&entry->list, &oper->entries))
		return true;

	if (ktime_compare(entry->end_time, oper->cycle_end_time) == 0)
		return true;

	return false;
}

static bool should_change_schedules(const struct sched_gate_list *admin,
				    const struct sched_gate_list *oper,
				    ktime_t end_time)
{
	ktime_t next_base_time, extension_time;

	if (!admin)
		return false;

	next_base_time = sched_base_time(admin);

	/* This is the simple case, the end_time would fall after
	 * the next schedule base_time.
	 */
	if (ktime_compare(next_base_time, end_time) <= 0)
		return true;

	/* This is the cycle_time_extension case, if the end_time
	 * plus the amount that can be extended would fall after the
	 * next schedule base_time, we can extend the current schedule
	 * for that amount.
	 */
	extension_time = ktime_add_ns(end_time, oper->cycle_time_extension);

	/* FIXME: the IEEE 802.1Q-2018 Specification isn't clear about
	 * how precisely the extension should be made. So after
	 * conformance testing, this logic may change.
	 */
	if (ktime_compare(next_base_time, extension_time) <= 0)
		return true;

	return false;
}

static enum hrtimer_restart advance_sched(struct hrtimer *timer)
{
	struct taprio_sched *q = container_of(timer, struct taprio_sched,
					      advance_timer);
	struct net_device *dev = qdisc_dev(q->root);
	struct sched_gate_list *oper, *admin;
	int num_tc = netdev_get_num_tc(dev);
	struct sched_entry *entry, *next;
	struct Qdisc *sch = q->root;
	ktime_t end_time;
	int tc;

	spin_lock(&q->current_entry_lock);
	entry = rcu_dereference_protected(q->current_entry,
					  lockdep_is_held(&q->current_entry_lock));
	oper = rcu_dereference_protected(q->oper_sched,
					 lockdep_is_held(&q->current_entry_lock));
	admin = rcu_dereference_protected(q->admin_sched,
					  lockdep_is_held(&q->current_entry_lock));

	if (!oper)
		switch_schedules(q, &admin, &oper);

	/* This can happen in two cases: 1. this is the very first run
	 * of this function (i.e. we weren't running any schedule
	 * previously); 2. The previous schedule just ended. The first
	 * entry of all schedules are pre-calculated during the
	 * schedule initialization.
	 */
	if (unlikely(!entry || entry->end_time == oper->base_time)) {
		next = list_first_entry(&oper->entries, struct sched_entry,
					list);
		end_time = next->end_time;
		goto first_run;
	}

	if (should_restart_cycle(oper, entry)) {
		next = list_first_entry(&oper->entries, struct sched_entry,
					list);
		oper->cycle_end_time = ktime_add_ns(oper->cycle_end_time,
						    oper->cycle_time);
	} else {
		next = list_next_entry(entry, list);
	}

	end_time = ktime_add_ns(entry->end_time, next->interval);
	end_time = min_t(ktime_t, end_time, oper->cycle_end_time);

	for (tc = 0; tc < num_tc; tc++) {
		if (next->gate_duration[tc] == oper->cycle_time)
			next->gate_close_time[tc] = KTIME_MAX;
		else
			next->gate_close_time[tc] = ktime_add_ns(entry->end_time,
								 next->gate_duration[tc]);
	}

	if (should_change_schedules(admin, oper, end_time)) {
		switch_schedules(q, &admin, &oper);
		/* After changing schedules, the next entry is the first one
		 * in the new schedule, with a pre-calculated end_time.
		 */
		next = list_first_entry(&oper->entries, struct sched_entry, list);
		end_time = next->end_time;
	}

	next->end_time = end_time;
	taprio_set_budgets(q, oper, next);

first_run:
	rcu_assign_pointer(q->current_entry, next);
	spin_unlock(&q->current_entry_lock);

	hrtimer_set_expires(&q->advance_timer, end_time);

	rcu_read_lock();
	__netif_schedule(sch);
	rcu_read_unlock();

	return HRTIMER_RESTART;
}

static const struct nla_policy entry_policy[TCA_TAPRIO_SCHED_ENTRY_MAX + 1] = {
	[TCA_TAPRIO_SCHED_ENTRY_INDEX]	   = { .type = NLA_U32 },
	[TCA_TAPRIO_SCHED_ENTRY_CMD]	   = { .type = NLA_U8 },
	[TCA_TAPRIO_SCHED_ENTRY_GATE_MASK] = { .type = NLA_U32 },
	[TCA_TAPRIO_SCHED_ENTRY_INTERVAL]  = { .type = NLA_U32 },
};

static const struct nla_policy taprio_tc_policy[TCA_TAPRIO_TC_ENTRY_MAX + 1] = {
	[TCA_TAPRIO_TC_ENTRY_INDEX]	   = NLA_POLICY_MAX(NLA_U32,
							    TC_QOPT_MAX_QUEUE - 1),
	[TCA_TAPRIO_TC_ENTRY_MAX_SDU]	   = { .type = NLA_U32 },
	[TCA_TAPRIO_TC_ENTRY_FP]	   = NLA_POLICY_RANGE(NLA_U32,
							      TC_FP_EXPRESS,
							      TC_FP_PREEMPTIBLE),
};

static const struct netlink_range_validation_signed taprio_cycle_time_range = {
	.min = 0,
	.max = INT_MAX,
};

static const struct nla_policy taprio_policy[TCA_TAPRIO_ATTR_MAX + 1] = {
	[TCA_TAPRIO_ATTR_PRIOMAP]	       = {
		.len = sizeof(struct tc_mqprio_qopt)
	},
	[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST]           = { .type = NLA_NESTED },
	[TCA_TAPRIO_ATTR_SCHED_BASE_TIME]            = { .type = NLA_S64 },
	[TCA_TAPRIO_ATTR_SCHED_SINGLE_ENTRY]         = { .type = NLA_NESTED },
	[TCA_TAPRIO_ATTR_SCHED_CLOCKID]              = { .type = NLA_S32 },
	[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]           =
		NLA_POLICY_FULL_RANGE_SIGNED(NLA_S64, &taprio_cycle_time_range),
	[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION] = { .type = NLA_S64 },
	[TCA_TAPRIO_ATTR_FLAGS]                      =
		NLA_POLICY_MASK(NLA_U32, TAPRIO_SUPPORTED_FLAGS),
	[TCA_TAPRIO_ATTR_TXTIME_DELAY]		     = { .type = NLA_U32 },
	[TCA_TAPRIO_ATTR_TC_ENTRY]		     = { .type = NLA_NESTED },
};

static int fill_sched_entry(struct taprio_sched *q, struct nlattr **tb,
			    struct sched_entry *entry,
			    struct netlink_ext_ack *extack)
{
	int min_duration = length_to_duration(q, ETH_ZLEN);
	u32 interval = 0;

	if (tb[TCA_TAPRIO_SCHED_ENTRY_CMD])
		entry->command = nla_get_u8(
			tb[TCA_TAPRIO_SCHED_ENTRY_CMD]);

	if (tb[TCA_TAPRIO_SCHED_ENTRY_GATE_MASK])
		entry->gate_mask = nla_get_u32(
			tb[TCA_TAPRIO_SCHED_ENTRY_GATE_MASK]);

	if (tb[TCA_TAPRIO_SCHED_ENTRY_INTERVAL])
		interval = nla_get_u32(
			tb[TCA_TAPRIO_SCHED_ENTRY_INTERVAL]);

	/* The interval should allow at least the minimum ethernet
	 * frame to go out.
	 */
	if (interval < min_duration) {
		NL_SET_ERR_MSG(extack, "Invalid interval for schedule entry");
		return -EINVAL;
	}

	entry->interval = interval;

	return 0;
}

static int parse_sched_entry(struct taprio_sched *q, struct nlattr *n,
			     struct sched_entry *entry, int index,
			     struct netlink_ext_ack *extack)
{
	struct nlattr *tb[TCA_TAPRIO_SCHED_ENTRY_MAX + 1] = { };
	int err;

	err = nla_parse_nested_deprecated(tb, TCA_TAPRIO_SCHED_ENTRY_MAX, n,
					  entry_policy, NULL);
	if (err < 0) {
		NL_SET_ERR_MSG(extack, "Could not parse nested entry");
		return -EINVAL;
	}

	entry->index = index;

	return fill_sched_entry(q, tb, entry, extack);
}

static int parse_sched_list(struct taprio_sched *q, struct nlattr *list,
			    struct sched_gate_list *sched,
			    struct netlink_ext_ack *extack)
{
	struct nlattr *n;
	int err, rem;
	int i = 0;

	if (!list)
		return -EINVAL;

	nla_for_each_nested(n, list, rem) {
		struct sched_entry *entry;

		if (nla_type(n) != TCA_TAPRIO_SCHED_ENTRY) {
			NL_SET_ERR_MSG(extack, "Attribute is not of type 'entry'");
			continue;
		}

		entry = kzalloc_obj(*entry);
		if (!entry) {
			NL_SET_ERR_MSG(extack, "Not enough memory for entry");
			return -ENOMEM;
		}

		err = parse_sched_entry(q, n, entry, i, extack);
		if (err < 0) {
			kfree(entry);
			return err;
		}

		list_add_tail(&entry->list, &sched->entries);
		i++;
	}

	sched->num_entries = i;

	return i;
}

static int parse_taprio_schedule(struct taprio_sched *q, struct nlattr **tb,
				 struct sched_gate_list *new,
				 struct netlink_ext_ack *extack)
{
	int err = 0;

	if (tb[TCA_TAPRIO_ATTR_SCHED_SINGLE_ENTRY]) {
		NL_SET_ERR_MSG(extack, "Adding a single entry is not supported");
		return -ENOTSUPP;
	}

	if (tb[TCA_TAPRIO_ATTR_SCHED_BASE_TIME])
		new->base_time = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_BASE_TIME]);

	if (tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION])
		new->cycle_time_extension = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION]);

	if (tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME])
		new->cycle_time = nla_get_s64(tb[TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME]);

	if (tb[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST])
		err = parse_sched_list(q, tb[TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST],
				       new, extack);
	if (err < 0)
		return err;

	if (!new->cycle_time) {
		struct sched_entry *entry;
		ktime_t cycle = 0;

		list_for_each_entry(entry, &new->entries, list)
			cycle = ktime_add_ns(cycle, entry->interval);

		if (cycle < 0 || cycle > INT_MAX) {
			NL_SET_ERR_MSG(extack, "'cycle_time' is too big");
			return -EINVAL;
		}

		new->cycle_time = cycle;
	}

	if (new->cycle_time < new->num_entries * length_to_duration(q, ETH_ZLEN)) {
		NL_SET_ERR_MSG(extack, "'cycle_time' is too small");
		return -EINVAL;
	}

	taprio_calculate_gate_durations(q, new);

	return 0;
}

static int taprio_parse_mqprio_opt(struct net_device *dev,
				   struct tc_mqprio_qopt *qopt,
				   struct netlink_ext_ack *extack,
				   u32 taprio_flags)
{
	bool allow_overlapping_txqs = TXTIME_ASSIST_IS_ENABLED(taprio_flags);

	if (!qopt) {
		if (!dev->num_tc) {
			NL_SET_ERR_MSG(extack, "'mqprio' configuration is necessary");
			return -EINVAL;
		}
		return 0;
	}

	/* taprio imposes that traffic classes map 1:n to tx queues */
	if (qopt->num_tc > dev->num_tx_queues) {
		NL_SET_ERR_MSG(extack, "Number of traffic classes is greater than number of HW queues");
		return -EINVAL;
	}

	/* For some reason, in txtime-assist mode, we allow TXQ ranges for
	 * different TCs to overlap, and just validate the TXQ ranges.
	 */
	return mqprio_validate_qopt(dev, qopt, true, allow_overlapping_txqs,
				    extack);
}

static int taprio_get_start_time(struct Qdisc *sch,
				 struct sched_gate_list *sched,
				 ktime_t *start)
{
	struct taprio_sched *q = qdisc_priv(sch);
	ktime_t now, base, cycle;
	s64 n;

	base = sched_base_time(sched);
	now = taprio_get_time(q);

	if (ktime_after(base, now)) {
		*start = base;
		return 0;
	}

	cycle = sched->cycle_time;

	/* The qdisc is expected to have at least one sched_entry.  Moreover,
	 * any entry must have 'interval' > 0. Thus if the cycle time is zero,
	 * something went really wrong. In that case, we should warn about this
	 * inconsistent state and return error.
	 */
	if (WARN_ON(!cycle))
		return -EFAULT;

	/* Schedule the start time for the beginning of the next
	 * cycle.
	 */
	n = div64_s64(ktime_sub_ns(now, base), cycle);
	*start = ktime_add_ns(base, (n + 1) * cycle);
	return 0;
}

static void setup_first_end_time(struct taprio_sched *q,
				 struct sched_gate_list *sched, ktime_t base)
{
	struct net_device *dev = qdisc_dev(q->root);
	int num_tc = netdev_get_num_tc(dev);
	struct sched_entry *first;
	ktime_t cycle;
	int tc;

	first = list_first_entry(&sched->entries,
				 struct sched_entry, list);

	cycle = sched->cycle_time;

	/* FIXME: find a better place to do this */
	sched->cycle_end_time = ktime_add_ns(base, cycle);

	first->end_time = ktime_add_ns(base, first->interval);
	taprio_set_budgets(q, sched, first);

	for (tc = 0; tc < num_tc; tc++) {
		if (first->gate_duration[tc] == sched->cycle_time)
			first->gate_close_time[tc] = KTIME_MAX;
		else
			first->gate_close_time[tc] = ktime_add_ns(base, first->gate_duration[tc]);
	}

	rcu_assign_pointer(q->current_entry, NULL);
}

static void taprio_start_sched(struct Qdisc *sch,
			       ktime_t start, struct sched_gate_list *new)
{
	struct taprio_sched *q = qdisc_priv(sch);
	ktime_t expires;

	if (FULL_OFFLOAD_IS_ENABLED(q->flags))
		return;

	expires = hrtimer_get_expires(&q->advance_timer);
	if (expires == 0)
		expires = KTIME_MAX;

	/* If the new schedule starts before the next expiration, we
	 * reprogram it to the earliest one, so we change the admin
	 * schedule to the operational one at the right time.
	 */
	start = min_t(ktime_t, start, expires);

	hrtimer_start(&q->advance_timer, start, HRTIMER_MODE_ABS);
}

static void taprio_set_picos_per_byte(struct net_device *dev,
				      struct taprio_sched *q,
				      struct netlink_ext_ack *extack)
{
	struct ethtool_link_ksettings ecmd;
	int speed = SPEED_10;
	int picos_per_byte;
	int err;

	err = netif_get_link_ksettings(dev, &ecmd);
	if (err < 0)
		goto skip;

	if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
		speed = ecmd.base.speed;

skip:
	picos_per_byte = (USEC_PER_SEC * 8) / speed;
	if (picos_per_byte < TAPRIO_PICOS_PER_BYTE_MIN) {
		if (!extack)
			pr_warn("Link speed %d is too high. Schedule may be inaccurate.\n",
				speed);
		NL_SET_ERR_MSG_FMT_MOD(extack,
				       "Link speed %d is too high. Schedule may be inaccurate.",
				       speed);
		picos_per_byte = TAPRIO_PICOS_PER_BYTE_MIN;
	}

	atomic64_set(&q->picos_per_byte, picos_per_byte);
	netdev_dbg(dev, "taprio: set %s's picos_per_byte to: %lld, linkspeed: %d\n",
		   dev->name, (long long)atomic64_read(&q->picos_per_byte),
		   speed);
}

static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event,
			       void *ptr)
{
	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct sched_gate_list *oper, *admin;
	struct qdisc_size_table *stab;
	struct taprio_sched *q;

	ASSERT_RTNL();

	if (event != NETDEV_UP && event != NETDEV_CHANGE)
		return NOTIFY_DONE;

	list_for_each_entry(q, &taprio_list, taprio_list) {
		if (dev != qdisc_dev(q->root))
			continue;

		taprio_set_picos_per_byte(dev, q, NULL);

		stab = rtnl_dereference(q->root->stab);

		rcu_read_lock();
		oper = rcu_dereference(q->oper_sched);
		if (oper)
			taprio_update_queue_max_sdu(q, oper, stab);

		admin = rcu_dereference(q->admin_sched);
		if (admin)
			taprio_update_queue_max_sdu(q, admin, stab);
		rcu_read_unlock();

		break;
	}

	return NOTIFY_DONE;
}

static void setup_txtime(struct taprio_sched *q,
			 struct sched_gate_list *sched, ktime_t base)
{
	struct sched_entry *entry;
	u64 interval = 0;

	list_for_each_entry(entry, &sched->entries, list) {
		entry->next_txtime = ktime_add_ns(base, interval);
		interval += entry->interval;
	}
}

static struct tc_taprio_qopt_offload *taprio_offload_alloc(int num_entries)
{
	struct __tc_taprio_qopt_offload *__offload;

	__offload = kzalloc_flex(*__offload, offload.entries, num_entries);
	if (!__offload)
		return NULL;

	refcount_set(&__offload->users, 1);

	return &__offload->offload;
}

struct tc_taprio_qopt_offload *taprio_offload_get(struct tc_taprio_qopt_offload
						  *offload)
{
	struct __tc_taprio_qopt_offload *__offload;

	__offload = container_of(offload, struct __tc_taprio_qopt_offload,
				 offload);

	refcount_inc(&__offload->users);

	return offload;
}
EXPORT_SYMBOL_GPL(taprio_offload_get);

void taprio_offload_free(struct tc_taprio_qopt_offload *offload)
{
	struct __tc_taprio_qopt_offload *__offload;

	__offload = container_of(offload, struct __tc_taprio_qopt_offload,
				 offload);

	if (!refcount_dec_and_test(&__offload->users))
		return;

	kfree(__offload);
}
EXPORT_SYMBOL_GPL(taprio_offload_free);

/* The function will only serve to keep the pointers to the "oper" and "admin"
 * schedules valid in relation to their base times, so when calling dump() the
 * users looks at the right schedules.
 * When using full offload, the admin configuration is promoted to oper at the
 * base_time in the PHC time domain.  But because the system time is not
 * necessarily in sync with that, we can't just trigger a hrtimer to call
 * switch_schedules at the right hardware time.
 * At the moment we call this by hand right away from taprio, but in the future
 * it will be useful to create a mechanism for drivers to notify taprio of the
 * offload state (PENDING, ACTIVE, INACTIVE) so it can be visible in dump().
 * This is left as TODO.
 */
static void taprio_offload_config_changed(struct taprio_sched *q)
{
	struct sched_gate_list *oper, *admin;

	oper = rtnl_dereference(q->oper_sched);
	admin = rtnl_dereference(q->admin_sched);

	switch_schedules(q, &admin, &oper);
}

static u32 tc_map_to_queue_mask(struct net_device *dev, u32 tc_mask)
{
	u32 i, queue_mask = 0;

	for (i = 0; i < dev->num_tc; i++) {
		u32 offset, count;

		if (!(tc_mask & BIT(i)))
			continue;

		offset = dev->tc_to_txq[i].offset;
		count = dev->tc_to_txq[i].count;

		queue_mask |= GENMASK(offset + count - 1, offset);
	}

	return queue_mask;
}

static void taprio_sched_to_offload(struct net_device *dev,
				    struct sched_gate_list *sched,
				    struct tc_taprio_qopt_offload *offload,
				    const struct tc_taprio_caps *caps)
{
	struct sched_entry *entry;
	int i = 0;

	offload->base_time = sched->base_time;
	offload->cycle_time = sched->cycle_time;
	offload->cycle_time_extension = sched->cycle_time_extension;

	list_for_each_entry(entry, &sched->entries, list) {
		struct tc_taprio_sched_entry *e = &offload->entries[i];

		e->command = entry->command;
		e->interval = entry->interval;
		if (caps->gate_mask_per_txq)
			e->gate_mask = tc_map_to_queue_mask(dev,
							    entry->gate_mask);
		else
			e->gate_mask = entry->gate_mask;

		i++;
	}

	offload->num_entries = i;
}

static void taprio_detect_broken_mqprio(struct taprio_sched *q)
{
	struct net_device *dev = qdisc_dev(q->root);
	struct tc_taprio_caps caps;

	qdisc_offload_query_caps(dev, TC_SETUP_QDISC_TAPRIO,
				 &caps, sizeof(caps));

	q->broken_mqprio = caps.broken_mqprio;
	if (q->broken_mqprio)
		static_branch_inc(&taprio_have_broken_mqprio);
	else
		static_branch_inc(&taprio_have_working_mqprio);

	q->detected_mqprio = true;
}

static void taprio_cleanup_broken_mqprio(struct taprio_sched *q)
{
	if (!q->detected_mqprio)
		return;

	if (q->broken_mqprio)
		static_branch_dec(&taprio_have_broken_mqprio);
	else
		static_branch_dec(&taprio_have_working_mqprio);
}

static int taprio_enable_offload(struct net_device *dev,
				 struct taprio_sched *q,
				 struct sched_gate_list *sched,
				 struct netlink_ext_ack *extack)
{
	const struct net_device_ops *ops = dev->netdev_ops;
	struct tc_taprio_qopt_offload *offload;
	struct tc_taprio_caps caps;
	int tc, err = 0;

	if (!ops->ndo_setup_tc) {
		NL_SET_ERR_MSG(extack,
			       "Device does not support taprio offload");
		return -EOPNOTSUPP;
	}

	qdisc_offload_query_caps(dev, TC_SETUP_QDISC_TAPRIO,
				 &caps, sizeof(caps));

	if (!caps.supports_queue_max_sdu) {
		for (tc = 0; tc < TC_MAX_QUEUE; tc++) {
			if (q->max_sdu[tc]) {
				NL_SET_ERR_MSG_MOD(extack,
						   "Device does not handle queueMaxSDU");
				return -EOPNOTSUPP;
			}
		}
	}

	offload = taprio_offload_alloc(sched->num_entries);
	if (!offload) {
		NL_SET_ERR_MSG(extack,
			       "Not enough memory for enabling offload mode");
		return -ENOMEM;
	}
	offload->cmd = TAPRIO_CMD_REPLACE;
	offload->extack = extack;
	mqprio_qopt_reconstruct(dev, &offload->mqprio.qopt);
	offload->mqprio.extack = extack;
	taprio_sched_to_offload(dev, sched, offload, &caps);
	mqprio_fp_to_offload(q->fp, &offload->mqprio);

	for (tc = 0; tc < TC_MAX_QUEUE; tc++)
		offload->max_sdu[tc] = q->max_sdu[tc];

	err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_TAPRIO, offload);
	if (err < 0) {
		NL_SET_ERR_MSG_WEAK(extack,
				    "Device failed to setup taprio offload");
		goto done;
	}

	q->offloaded = true;

done:
	/* The offload structure may linger around via a reference taken by the
	 * device driver, so clear up the netlink extack pointer so that the
	 * driver isn't tempted to dereference data which stopped being valid
	 */
	offload->extack = NULL;
	offload->mqprio.extack = NULL;
	taprio_offload_free(offload);

	return err;
}

static int taprio_disable_offload(struct net_device *dev,
				  struct taprio_sched *q,
				  struct netlink_ext_ack *extack)
{
	const struct net_device_ops *ops = dev->netdev_ops;
	struct tc_taprio_qopt_offload *offload;
	int err;

	if (!q->offloaded)
		return 0;

	offload = taprio_offload_alloc(0);
	if (!offload) {
		NL_SET_ERR_MSG(extack,
			       "Not enough memory to disable offload mode");
		return -ENOMEM;
	}
	offload->cmd = TAPRIO_CMD_DESTROY;

	err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_TAPRIO, offload);
	if (err < 0) {
		NL_SET_ERR_MSG(extack,
			       "Device failed to disable offload");
		goto out;
	}

	q->offloaded = false;

out:
	taprio_offload_free(offload);

	return err;
}

/* If full offload is enabled, the only possible clockid is the net device's
 * PHC. For that reason, specifying a clockid through netlink is incorrect.
 * For txtime-assist, it is implicitly assumed that the device's PHC is kept
 * in sync with the specified clockid via a user space daemon such as phc2sys.
 * For both software taprio and txtime-assist, the clockid is used for the
 * hrtimer that advances the schedule and hence mandatory.
 */
static int taprio_parse_clockid(struct Qdisc *sch, struct nlattr **tb,
				struct netlink_ext_ack *extack)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	int err = -EINVAL;

	if (FULL_OFFLOAD_IS_ENABLED(q->flags)) {
		const struct ethtool_ops *ops = dev->ethtool_ops;
		struct kernel_ethtool_ts_info info = {
			.cmd = ETHTOOL_GET_TS_INFO,
			.phc_index = -1,
		};

		if (tb[TCA_TAPRIO_ATTR_SCHED_CLOCKID]) {
			NL_SET_ERR_MSG(extack,
				       "The 'clockid' cannot be specified for full offload");
			goto out;
		}

		if (ops && ops->get_ts_info)
			err = ops->get_ts_info(dev, &info);

		if (err || info.phc_index < 0) {
			NL_SET_ERR_MSG(extack,
				       "Device does not have a PTP clock");
			err = -ENOTSUPP;
			goto out;
		}
	} else if (tb[TCA_TAPRIO_ATTR_SCHED_CLOCKID]) {
		int clockid = nla_get_s32(tb[TCA_TAPRIO_ATTR_SCHED_CLOCKID]);
		enum tk_offsets tk_offset;

		/* We only support static clockids and we don't allow
		 * for it to be modified after the first init.
		 */
		if (clockid < 0 ||
		    (q->clockid != -1 && q->clockid != clockid)) {
			NL_SET_ERR_MSG(extack,
				       "Changing the 'clockid' of a running schedule is not supported");
			err = -ENOTSUPP;
			goto out;
		}

		switch (clockid) {
		case CLOCK_REALTIME:
			tk_offset = TK_OFFS_REAL;
			break;
		case CLOCK_MONOTONIC:
			tk_offset = TK_OFFS_MAX;
			break;
		case CLOCK_BOOTTIME:
			tk_offset = TK_OFFS_BOOT;
			break;
		case CLOCK_TAI:
			tk_offset = TK_OFFS_TAI;
			break;
		default:
			NL_SET_ERR_MSG(extack, "Invalid 'clockid'");
			err = -EINVAL;
			goto out;
		}
		/* This pairs with READ_ONCE() in taprio_mono_to_any */
		WRITE_ONCE(q->tk_offset, tk_offset);

		q->clockid = clockid;
	} else {
		NL_SET_ERR_MSG(extack, "Specifying a 'clockid' is mandatory");
		goto out;
	}

	/* Everything went ok, return success. */
	err = 0;

out:
	return err;
}

static int taprio_parse_tc_entry(struct Qdisc *sch,
				 struct nlattr *opt,
				 u32 max_sdu[TC_QOPT_MAX_QUEUE],
				 u32 fp[TC_QOPT_MAX_QUEUE],
				 unsigned long *seen_tcs,
				 struct netlink_ext_ack *extack)
{
	struct nlattr *tb[TCA_TAPRIO_TC_ENTRY_MAX + 1] = { };
	struct net_device *dev = qdisc_dev(sch);
	int err, tc;
	u32 val;

	err = nla_parse_nested(tb, TCA_TAPRIO_TC_ENTRY_MAX, opt,
			       taprio_tc_policy, extack);
	if (err < 0)
		return err;

	if (NL_REQ_ATTR_CHECK(extack, opt, tb, TCA_TAPRIO_TC_ENTRY_INDEX)) {
		NL_SET_ERR_MSG_MOD(extack, "TC entry index missing");
		return -EINVAL;
	}

	tc = nla_get_u32(tb[TCA_TAPRIO_TC_ENTRY_INDEX]);
	if (*seen_tcs & BIT(tc)) {
		NL_SET_ERR_MSG_ATTR(extack, tb[TCA_TAPRIO_TC_ENTRY_INDEX],
				    "Duplicate tc entry");
		return -EINVAL;
	}

	*seen_tcs |= BIT(tc);

	if (tb[TCA_TAPRIO_TC_ENTRY_MAX_SDU]) {
		val = nla_get_u32(tb[TCA_TAPRIO_TC_ENTRY_MAX_SDU]);
		if (val > dev->max_mtu) {
			NL_SET_ERR_MSG_MOD(extack, "TC max SDU exceeds device max MTU");
			return -ERANGE;
		}

		max_sdu[tc] = val;
	}

	if (tb[TCA_TAPRIO_TC_ENTRY_FP])
		fp[tc] = nla_get_u32(tb[TCA_TAPRIO_TC_ENTRY_FP]);

	return 0;
}

static int taprio_parse_tc_entries(struct Qdisc *sch,
				   struct nlattr *opt,
				   struct netlink_ext_ack *extack)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	u32 max_sdu[TC_QOPT_MAX_QUEUE];
	bool have_preemption = false;
	unsigned long seen_tcs = 0;
	u32 fp[TC_QOPT_MAX_QUEUE];
	struct nlattr *n;
	int tc, rem;
	int err = 0;

	for (tc = 0; tc < TC_QOPT_MAX_QUEUE; tc++) {
		max_sdu[tc] = q->max_sdu[tc];
		fp[tc] = q->fp[tc];
	}

	nla_for_each_nested_type(n, TCA_TAPRIO_ATTR_TC_ENTRY, opt, rem) {
		err = taprio_parse_tc_entry(sch, n, max_sdu, fp, &seen_tcs,
					    extack);
		if (err)
			return err;
	}

	for (tc = 0; tc < TC_QOPT_MAX_QUEUE; tc++) {
		WRITE_ONCE(q->max_sdu[tc], max_sdu[tc]);
		WRITE_ONCE(q->fp[tc], fp[tc]);
		if (fp[tc] != TC_FP_EXPRESS)
			have_preemption = true;
	}

	if (have_preemption) {
		if (!FULL_OFFLOAD_IS_ENABLED(q->flags)) {
			NL_SET_ERR_MSG(extack,
				       "Preemption only supported with full offload");
			return -EOPNOTSUPP;
		}

		if (!ethtool_dev_mm_supported(dev)) {
			NL_SET_ERR_MSG(extack,
				       "Device does not support preemption");
			return -EOPNOTSUPP;
		}
	}

	return err;
}

static int taprio_mqprio_cmp(const struct net_device *dev,
			     const struct tc_mqprio_qopt *mqprio)
{
	int i;

	if (!mqprio || mqprio->num_tc != dev->num_tc)
		return -1;

	for (i = 0; i < mqprio->num_tc; i++)
		if (dev->tc_to_txq[i].count != mqprio->count[i] ||
		    dev->tc_to_txq[i].offset != mqprio->offset[i])
			return -1;

	for (i = 0; i <= TC_BITMASK; i++)
		if (dev->prio_tc_map[i] != mqprio->prio_tc_map[i])
			return -1;

	return 0;
}

static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
			 struct netlink_ext_ack *extack)
{
	struct qdisc_size_table *stab = rtnl_dereference(sch->stab);
	struct nlattr *tb[TCA_TAPRIO_ATTR_MAX + 1] = { };
	struct sched_gate_list *oper, *admin, *new_admin;
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	struct tc_mqprio_qopt *mqprio = NULL;
	unsigned long flags;
	u32 taprio_flags;
	ktime_t start;
	int i, err;

	err = nla_parse_nested_deprecated(tb, TCA_TAPRIO_ATTR_MAX, opt,
					  taprio_policy, extack);
	if (err < 0)
		return err;

	if (tb[TCA_TAPRIO_ATTR_PRIOMAP])
		mqprio = nla_data(tb[TCA_TAPRIO_ATTR_PRIOMAP]);

	/* The semantics of the 'flags' argument in relation to 'change()'
	 * requests, are interpreted following two rules (which are applied in
	 * this order): (1) an omitted 'flags' argument is interpreted as
	 * zero; (2) the 'flags' of a "running" taprio instance cannot be
	 * changed.
	 */
	taprio_flags = nla_get_u32_default(tb[TCA_TAPRIO_ATTR_FLAGS], 0);

	/* txtime-assist and full offload are mutually exclusive */
	if ((taprio_flags & TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST) &&
	    (taprio_flags & TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)) {
		NL_SET_ERR_MSG_ATTR(extack, tb[TCA_TAPRIO_ATTR_FLAGS],
				    "TXTIME_ASSIST and FULL_OFFLOAD are mutually exclusive");
		return -EINVAL;
	}

	if (q->flags != taprio_flags) {
		if (q->flags != TAPRIO_FLAGS_INVALID) {
			NL_SET_ERR_MSG_MOD(extack,
					   "Changing 'flags' of a running schedule is not supported");
			return -EOPNOTSUPP;
		}
		WRITE_ONCE(q->flags, taprio_flags);
	}

	/* Needed for length_to_duration() during netlink attribute parsing */
	taprio_set_picos_per_byte(dev, q, extack);

	err = taprio_parse_mqprio_opt(dev, mqprio, extack, q->flags);
	if (err < 0)
		return err;

	err = taprio_parse_tc_entries(sch, opt, extack);
	if (err)
		return err;

	new_admin = kzalloc_obj(*new_admin);
	if (!new_admin) {
		NL_SET_ERR_MSG(extack, "Not enough memory for a new schedule");
		return -ENOMEM;
	}
	INIT_LIST_HEAD(&new_admin->entries);

	oper = rtnl_dereference(q->oper_sched);
	admin = rtnl_dereference(q->admin_sched);

	/* no changes - no new mqprio settings */
	if (!taprio_mqprio_cmp(dev, mqprio))
		mqprio = NULL;

	if (mqprio && (oper || admin)) {
		NL_SET_ERR_MSG(extack, "Changing the traffic mapping of a running schedule is not supported");
		err = -ENOTSUPP;
		goto free_sched;
	}

	if (mqprio) {
		err = netdev_set_num_tc(dev, mqprio->num_tc);
		if (err)
			goto free_sched;
		for (i = 0; i < mqprio->num_tc; i++) {
			netdev_set_tc_queue(dev, i,
					    mqprio->count[i],
					    mqprio->offset[i]);
			q->cur_txq[i] = mqprio->offset[i];
		}

		/* Always use supplied priority mappings */
		for (i = 0; i <= TC_BITMASK; i++)
			netdev_set_prio_tc_map(dev, i,
					       mqprio->prio_tc_map[i]);
	}

	err = parse_taprio_schedule(q, tb, new_admin, extack);
	if (err < 0)
		goto free_sched;

	if (new_admin->num_entries == 0) {
		NL_SET_ERR_MSG(extack, "There should be at least one entry in the schedule");
		err = -EINVAL;
		goto free_sched;
	}

	err = taprio_parse_clockid(sch, tb, extack);
	if (err < 0)
		goto free_sched;

	taprio_update_queue_max_sdu(q, new_admin, stab);

	if (FULL_OFFLOAD_IS_ENABLED(q->flags))
		err = taprio_enable_offload(dev, q, new_admin, extack);
	else
		err = taprio_disable_offload(dev, q, extack);
	if (err)
		goto free_sched;

	/* Protects against enqueue()/dequeue() */
	spin_lock_bh(qdisc_lock(sch));

	if (tb[TCA_TAPRIO_ATTR_TXTIME_DELAY]) {
		if (!TXTIME_ASSIST_IS_ENABLED(q->flags)) {
			NL_SET_ERR_MSG_MOD(extack, "txtime-delay can only be set when txtime-assist mode is enabled");
			err = -EINVAL;
			goto unlock;
		}

		WRITE_ONCE(q->txtime_delay,
			   nla_get_u32(tb[TCA_TAPRIO_ATTR_TXTIME_DELAY]));
	}

	if (!TXTIME_ASSIST_IS_ENABLED(q->flags) &&
	    !FULL_OFFLOAD_IS_ENABLED(q->flags) &&
	    !hrtimer_active(&q->advance_timer)) {
		hrtimer_setup(&q->advance_timer, advance_sched, q->clockid, HRTIMER_MODE_ABS);
	}

	err = taprio_get_start_time(sch, new_admin, &start);
	if (err < 0) {
		NL_SET_ERR_MSG(extack, "Internal error: failed get start time");
		goto unlock;
	}

	setup_txtime(q, new_admin, start);

	if (TXTIME_ASSIST_IS_ENABLED(q->flags)) {
		if (!oper) {
			rcu_assign_pointer(q->oper_sched, new_admin);
			err = 0;
			new_admin = NULL;
			goto unlock;
		}

		/* Not going to race against advance_sched(), but still */
		admin = rcu_replace_pointer(q->admin_sched, new_admin,
					    lockdep_rtnl_is_held());
		if (admin)
			call_rcu(&admin->rcu, taprio_free_sched_cb);
	} else {
		setup_first_end_time(q, new_admin, start);

		/* Protects against advance_sched() */
		spin_lock_irqsave(&q->current_entry_lock, flags);

		taprio_start_sched(sch, start, new_admin);

		admin = rcu_replace_pointer(q->admin_sched, new_admin,
					    lockdep_rtnl_is_held());
		if (admin)
			call_rcu(&admin->rcu, taprio_free_sched_cb);

		spin_unlock_irqrestore(&q->current_entry_lock, flags);

		if (FULL_OFFLOAD_IS_ENABLED(q->flags))
			taprio_offload_config_changed(q);
	}

	new_admin = NULL;
	err = 0;

	if (!stab)
		NL_SET_ERR_MSG_MOD(extack,
				   "Size table not specified, frame length estimations may be inaccurate");

unlock:
	spin_unlock_bh(qdisc_lock(sch));

free_sched:
	if (new_admin)
		call_rcu(&new_admin->rcu, taprio_free_sched_cb);

	return err;
}

static void taprio_reset(struct Qdisc *sch)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	int i;

	hrtimer_cancel(&q->advance_timer);

	if (q->qdiscs) {
		for (i = 0; i < dev->num_tx_queues; i++)
			if (q->qdiscs[i])
				qdisc_reset(q->qdiscs[i]);
	}
}

static void taprio_destroy(struct Qdisc *sch)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	struct sched_gate_list *oper, *admin;
	unsigned int i;

	list_del(&q->taprio_list);

	/* Note that taprio_reset() might not be called if an error
	 * happens in qdisc_create(), after taprio_init() has been called.
	 */
	hrtimer_cancel(&q->advance_timer);
	qdisc_synchronize(sch);

	taprio_disable_offload(dev, q, NULL);

	if (q->qdiscs) {
		for (i = 0; i < dev->num_tx_queues; i++)
			qdisc_put(q->qdiscs[i]);

		kfree(q->qdiscs);
	}
	q->qdiscs = NULL;

	netdev_reset_tc(dev);

	oper = rtnl_dereference(q->oper_sched);
	admin = rtnl_dereference(q->admin_sched);

	if (oper)
		call_rcu(&oper->rcu, taprio_free_sched_cb);

	if (admin)
		call_rcu(&admin->rcu, taprio_free_sched_cb);

	taprio_cleanup_broken_mqprio(q);
}

static int taprio_init(struct Qdisc *sch, struct nlattr *opt,
		       struct netlink_ext_ack *extack)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	int i, tc;

	spin_lock_init(&q->current_entry_lock);

	hrtimer_setup(&q->advance_timer, advance_sched, CLOCK_TAI, HRTIMER_MODE_ABS);

	q->root = sch;

	/* We only support static clockids. Use an invalid value as default
	 * and get the valid one on taprio_change().
	 */
	q->clockid = -1;
	q->flags = TAPRIO_FLAGS_INVALID;

	list_add(&q->taprio_list, &taprio_list);

	if (sch->parent != TC_H_ROOT) {
		NL_SET_ERR_MSG_MOD(extack, "Can only be attached as root qdisc");
		return -EOPNOTSUPP;
	}

	if (!netif_is_multiqueue(dev)) {
		NL_SET_ERR_MSG_MOD(extack, "Multi-queue device is required");
		return -EOPNOTSUPP;
	}

	q->qdiscs = kzalloc_objs(q->qdiscs[0], dev->num_tx_queues);
	if (!q->qdiscs)
		return -ENOMEM;

	if (!opt)
		return -EINVAL;

	for (i = 0; i < dev->num_tx_queues; i++) {
		struct netdev_queue *dev_queue;
		struct Qdisc *qdisc;

		dev_queue = netdev_get_tx_queue(dev, i);
		qdisc = qdisc_create_dflt(dev_queue,
					  &pfifo_qdisc_ops,
					  TC_H_MAKE(TC_H_MAJ(sch->handle),
						    TC_H_MIN(i + 1)),
					  extack);
		if (!qdisc)
			return -ENOMEM;

		if (i < dev->real_num_tx_queues)
			qdisc_hash_add(qdisc, false);

		q->qdiscs[i] = qdisc;
	}

	for (tc = 0; tc < TC_QOPT_MAX_QUEUE; tc++)
		q->fp[tc] = TC_FP_EXPRESS;

	taprio_detect_broken_mqprio(q);

	return taprio_change(sch, opt, extack);
}

static void taprio_attach(struct Qdisc *sch)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	unsigned int ntx;

	/* Attach underlying qdisc */
	for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
		struct netdev_queue *dev_queue = netdev_get_tx_queue(dev, ntx);
		struct Qdisc *old, *dev_queue_qdisc;

		if (FULL_OFFLOAD_IS_ENABLED(q->flags)) {
			struct Qdisc *qdisc = q->qdiscs[ntx];

			/* In offload mode, the root taprio qdisc is bypassed
			 * and the netdev TX queues see the children directly
			 */
			qdisc->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
			dev_queue_qdisc = qdisc;
		} else {
			/* In software mode, attach the root taprio qdisc
			 * to all netdev TX queues, so that dev_qdisc_enqueue()
			 * goes through taprio_enqueue().
			 */
			dev_queue_qdisc = sch;
		}
		old = dev_graft_qdisc(dev_queue, dev_queue_qdisc);
		/* The qdisc's refcount requires to be elevated once
		 * for each netdev TX queue it is grafted onto
		 */
		qdisc_refcount_inc(dev_queue_qdisc);
		if (old)
			qdisc_put(old);
	}
}

static struct netdev_queue *taprio_queue_get(struct Qdisc *sch,
					     unsigned long cl)
{
	struct net_device *dev = qdisc_dev(sch);
	unsigned long ntx = cl - 1;

	if (ntx >= dev->num_tx_queues)
		return NULL;

	return netdev_get_tx_queue(dev, ntx);
}

static int taprio_graft(struct Qdisc *sch, unsigned long cl,
			struct Qdisc *new, struct Qdisc **old,
			struct netlink_ext_ack *extack)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	struct netdev_queue *dev_queue = taprio_queue_get(sch, cl);

	if (!dev_queue)
		return -EINVAL;

	if (!new)
		new = &noop_qdisc;

	if (dev->flags & IFF_UP)
		dev_deactivate(dev, false);

	/* In offload mode, the child Qdisc is directly attached to the netdev
	 * TX queue, and thus, we need to keep its refcount elevated in order
	 * to counteract qdisc_graft()'s call to qdisc_put() once per TX queue.
	 * However, save the reference to the new qdisc in the private array in
	 * both software and offload cases, to have an up-to-date reference to
	 * our children.
	 */
	*old = q->qdiscs[cl - 1];
	if (FULL_OFFLOAD_IS_ENABLED(q->flags)) {
		WARN_ON_ONCE(dev_graft_qdisc(dev_queue, new) != *old);
		if (new != &noop_qdisc)
			qdisc_refcount_inc(new);
		if (*old && *old != &noop_qdisc)
			qdisc_put(*old);
	}

	q->qdiscs[cl - 1] = new;
	if (new != &noop_qdisc)
		new->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;

	if (dev->flags & IFF_UP)
		dev_activate(dev);

	return 0;
}

static int dump_entry(struct sk_buff *msg,
		      const struct sched_entry *entry)
{
	struct nlattr *item;

	item = nla_nest_start_noflag(msg, TCA_TAPRIO_SCHED_ENTRY);
	if (!item)
		return -ENOSPC;

	if (nla_put_u32(msg, TCA_TAPRIO_SCHED_ENTRY_INDEX, entry->index))
		goto nla_put_failure;

	if (nla_put_u8(msg, TCA_TAPRIO_SCHED_ENTRY_CMD, entry->command))
		goto nla_put_failure;

	if (nla_put_u32(msg, TCA_TAPRIO_SCHED_ENTRY_GATE_MASK,
			entry->gate_mask))
		goto nla_put_failure;

	if (nla_put_u32(msg, TCA_TAPRIO_SCHED_ENTRY_INTERVAL,
			entry->interval))
		goto nla_put_failure;

	return nla_nest_end(msg, item);

nla_put_failure:
	nla_nest_cancel(msg, item);
	return -1;
}

static int dump_schedule(struct sk_buff *msg,
			 const struct sched_gate_list *root)
{
	struct nlattr *entry_list;
	struct sched_entry *entry;

	if (nla_put_s64(msg, TCA_TAPRIO_ATTR_SCHED_BASE_TIME,
			root->base_time, TCA_TAPRIO_PAD))
		return -1;

	if (nla_put_s64(msg, TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME,
			root->cycle_time, TCA_TAPRIO_PAD))
		return -1;

	if (nla_put_s64(msg, TCA_TAPRIO_ATTR_SCHED_CYCLE_TIME_EXTENSION,
			root->cycle_time_extension, TCA_TAPRIO_PAD))
		return -1;

	entry_list = nla_nest_start_noflag(msg,
					   TCA_TAPRIO_ATTR_SCHED_ENTRY_LIST);
	if (!entry_list)
		goto error_nest;

	list_for_each_entry(entry, &root->entries, list) {
		if (dump_entry(msg, entry) < 0)
			goto error_nest;
	}

	nla_nest_end(msg, entry_list);
	return 0;

error_nest:
	nla_nest_cancel(msg, entry_list);
	return -1;
}

static int taprio_dump_tc_entries(struct sk_buff *skb,
				  const struct taprio_sched *q,
				  const struct sched_gate_list *sched)
{
	struct nlattr *n;
	int tc;

	for (tc = 0; tc < TC_MAX_QUEUE; tc++) {
		n = nla_nest_start(skb, TCA_TAPRIO_ATTR_TC_ENTRY);
		if (!n)
			return -EMSGSIZE;

		if (nla_put_u32(skb, TCA_TAPRIO_TC_ENTRY_INDEX, tc))
			goto nla_put_failure;

		if (nla_put_u32(skb, TCA_TAPRIO_TC_ENTRY_MAX_SDU,
				READ_ONCE(sched->max_sdu[tc])))
			goto nla_put_failure;

		if (nla_put_u32(skb, TCA_TAPRIO_TC_ENTRY_FP,
				READ_ONCE(q->fp[tc])))
			goto nla_put_failure;

		nla_nest_end(skb, n);
	}

	return 0;

nla_put_failure:
	nla_nest_cancel(skb, n);
	return -EMSGSIZE;
}

static int taprio_put_stat(struct sk_buff *skb, u64 val, u16 attrtype)
{
	if (val == TAPRIO_STAT_NOT_SET)
		return 0;
	if (nla_put_u64_64bit(skb, attrtype, val, TCA_TAPRIO_OFFLOAD_STATS_PAD))
		return -EMSGSIZE;
	return 0;
}

static int taprio_dump_xstats(struct Qdisc *sch, struct gnet_dump *d,
			      struct tc_taprio_qopt_offload *offload,
			      struct tc_taprio_qopt_stats *stats)
{
	struct net_device *dev = qdisc_dev(sch);
	const struct net_device_ops *ops;
	struct sk_buff *skb = d->skb;
	struct nlattr *xstats;
	int err;

	ops = qdisc_dev(sch)->netdev_ops;

	/* FIXME I could use qdisc_offload_dump_helper(), but that messes
	 * with sch->flags depending on whether the device reports taprio
	 * stats, and I'm not sure whether that's a good idea, considering
	 * that stats are optional to the offload itself
	 */
	if (!ops->ndo_setup_tc)
		return 0;

	memset(stats, 0xff, sizeof(*stats));

	err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_TAPRIO, offload);
	if (err == -EOPNOTSUPP)
		return 0;
	if (err)
		return err;

	xstats = nla_nest_start(skb, TCA_STATS_APP);
	if (!xstats)
		goto err;

	if (taprio_put_stat(skb, stats->window_drops,
			    TCA_TAPRIO_OFFLOAD_STATS_WINDOW_DROPS) ||
	    taprio_put_stat(skb, stats->tx_overruns,
			    TCA_TAPRIO_OFFLOAD_STATS_TX_OVERRUNS))
		goto err_cancel;

	nla_nest_end(skb, xstats);

	return 0;

err_cancel:
	nla_nest_cancel(skb, xstats);
err:
	return -EMSGSIZE;
}

static int taprio_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
	struct tc_taprio_qopt_offload offload = {
		.cmd = TAPRIO_CMD_STATS,
	};

	return taprio_dump_xstats(sch, d, &offload, &offload.stats);
}

static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	struct sched_gate_list *oper, *admin;
	struct tc_mqprio_qopt opt = { 0 };
	struct nlattr *nest, *sched_nest;
	u32 txtime_delay;

	mqprio_qopt_reconstruct(dev, &opt);

	nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
	if (!nest)
		goto start_error;

	if (nla_put(skb, TCA_TAPRIO_ATTR_PRIOMAP, sizeof(opt), &opt))
		goto options_error;

	if (!FULL_OFFLOAD_IS_ENABLED(q->flags) &&
	    nla_put_s32(skb, TCA_TAPRIO_ATTR_SCHED_CLOCKID, q->clockid))
		goto options_error;

	if (q->flags && nla_put_u32(skb, TCA_TAPRIO_ATTR_FLAGS, q->flags))
		goto options_error;

	txtime_delay = READ_ONCE(q->txtime_delay);
	if (txtime_delay &&
	    nla_put_u32(skb, TCA_TAPRIO_ATTR_TXTIME_DELAY, txtime_delay))
		goto options_error;

	rcu_read_lock();

	oper = rcu_dereference(q->oper_sched);
	admin = rcu_dereference(q->admin_sched);

	if (oper && taprio_dump_tc_entries(skb, q, oper))
		goto options_error_rcu;

	if (oper && dump_schedule(skb, oper))
		goto options_error_rcu;

	if (!admin)
		goto done;

	sched_nest = nla_nest_start_noflag(skb, TCA_TAPRIO_ATTR_ADMIN_SCHED);
	if (!sched_nest)
		goto options_error_rcu;

	if (dump_schedule(skb, admin))
		goto admin_error;

	nla_nest_end(skb, sched_nest);

done:
	rcu_read_unlock();
	return nla_nest_end(skb, nest);

admin_error:
	nla_nest_cancel(skb, sched_nest);

options_error_rcu:
	rcu_read_unlock();

options_error:
	nla_nest_cancel(skb, nest);

start_error:
	return -ENOSPC;
}

static struct Qdisc *taprio_leaf(struct Qdisc *sch, unsigned long cl)
{
	struct taprio_sched *q = qdisc_priv(sch);
	struct net_device *dev = qdisc_dev(sch);
	unsigned int ntx = cl - 1;

	if (ntx >= dev->num_tx_queues)
		return NULL;

	return q->qdiscs[ntx];
}

static unsigned long taprio_find(struct Qdisc *sch, u32 classid)
{
	unsigned int ntx = TC_H_MIN(classid);

	if (!taprio_queue_get(sch, ntx))
		return 0;
	return ntx;
}

static int taprio_dump_class(struct Qdisc *sch, unsigned long cl,
			     struct sk_buff *skb, struct tcmsg *tcm)
{
	struct Qdisc *child = taprio_leaf(sch, cl);

	tcm->tcm_parent = TC_H_ROOT;
	tcm->tcm_handle |= TC_H_MIN(cl);
	tcm->tcm_info = child->handle;

	return 0;
}

static int taprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
				   struct gnet_dump *d)
	__releases(d->lock)
	__acquires(d->lock)
{
	struct Qdisc *child = taprio_leaf(sch, cl);
	struct tc_taprio_qopt_offload offload = {
		.cmd = TAPRIO_CMD_QUEUE_STATS,
		.queue_stats = {
			.queue = cl - 1,
		},
	};

	if (gnet_stats_copy_basic(d, NULL, &child->bstats, true) < 0 ||
	    qdisc_qstats_copy(d, child) < 0)
		return -1;

	return taprio_dump_xstats(sch, d, &offload, &offload.queue_stats.stats);
}

static void taprio_walk(struct Qdisc *sch, struct qdisc_walker *arg)
{
	struct net_device *dev = qdisc_dev(sch);
	unsigned long ntx;

	if (arg->stop)
		return;

	arg->count = arg->skip;
	for (ntx = arg->skip; ntx < dev->num_tx_queues; ntx++) {
		if (!tc_qdisc_stats_dump(sch, ntx + 1, arg))
			break;
	}
}

static struct netdev_queue *taprio_select_queue(struct Qdisc *sch,
						struct tcmsg *tcm)
{
	return taprio_queue_get(sch, TC_H_MIN(tcm->tcm_parent));
}

static const struct Qdisc_class_ops taprio_class_ops = {
	.graft		= taprio_graft,
	.leaf		= taprio_leaf,
	.find		= taprio_find,
	.walk		= taprio_walk,
	.dump		= taprio_dump_class,
	.dump_stats	= taprio_dump_class_stats,
	.select_queue	= taprio_select_queue,
};

static struct Qdisc_ops taprio_qdisc_ops __read_mostly = {
	.cl_ops		= &taprio_class_ops,
	.id		= "taprio",
	.priv_size	= sizeof(struct taprio_sched),
	.init		= taprio_init,
	.change		= taprio_change,
	.destroy	= taprio_destroy,
	.reset		= taprio_reset,
	.attach		= taprio_attach,
	.peek		= taprio_peek,
	.dequeue	= taprio_dequeue,
	.enqueue	= taprio_enqueue,
	.dump		= taprio_dump,
	.dump_stats	= taprio_dump_stats,
	.owner		= THIS_MODULE,
};
MODULE_ALIAS_NET_SCH("taprio");

static struct notifier_block taprio_device_notifier = {
	.notifier_call = taprio_dev_notifier,
};

static int __init taprio_module_init(void)
{
	int err = register_netdevice_notifier(&taprio_device_notifier);

	if (err)
		return err;

	return register_qdisc(&taprio_qdisc_ops);
}

static void __exit taprio_module_exit(void)
{
	unregister_qdisc(&taprio_qdisc_ops);
	unregister_netdevice_notifier(&taprio_device_notifier);
}

module_init(taprio_module_init);
module_exit(taprio_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Time Aware Priority qdisc");