/*
 * Copyright © 2015 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 */

#include <linux/kthread.h>

#include "i915_drv.h"

static void intel_breadcrumbs_hangcheck(unsigned long data)
{
        struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
        struct intel_breadcrumbs *b = &engine->breadcrumbs;

        if (!b->irq_enabled)
                return;

        if (time_before(jiffies, b->timeout)) {
                mod_timer(&b->hangcheck, b->timeout);
                return;
        }

        DRM_DEBUG("Hangcheck timer elapsed... %s idle\n", engine->name);
        set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
        mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);

        /* Ensure that even if the GPU hangs, we get woken up.
         *
         * However, note that if no one is waiting, we never notice
         * a gpu hang. Eventually, we will have to wait for a resource
         * held by the GPU and so trigger a hangcheck. In the most
         * pathological case, this will be upon memory starvation! To
         * prevent this, we also queue the hangcheck from the retire
         * worker.
         */
        i915_queue_hangcheck(engine->i915);
}

static unsigned long wait_timeout(void)
{
        return round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
}

static void intel_breadcrumbs_fake_irq(unsigned long data)
{
        struct intel_engine_cs *engine = (struct intel_engine_cs *)data;

        /*
         * The timer persists in case we cannot enable interrupts,
         * or if we have previously seen seqno/interrupt incoherency
         * ("missed interrupt" syndrome). Here the worker will wake up
         * every jiffie in order to kick the oldest waiter to do the
         * coherent seqno check.
         */
        if (intel_engine_wakeup(engine))
                mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
}

static void irq_enable(struct intel_engine_cs *engine)
{
        /* Enabling the IRQ may miss the generation of the interrupt, but
         * we still need to force the barrier before reading the seqno,
         * just in case.
         */
        engine->breadcrumbs.irq_posted = true;

        spin_lock_irq(&engine->i915->irq_lock);
        engine->irq_enable(engine);
        spin_unlock_irq(&engine->i915->irq_lock);
}

static void irq_disable(struct intel_engine_cs *engine)
{
        spin_lock_irq(&engine->i915->irq_lock);
        engine->irq_disable(engine);
        spin_unlock_irq(&engine->i915->irq_lock);

        engine->breadcrumbs.irq_posted = false;
}

static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
{
        struct intel_engine_cs *engine =
                container_of(b, struct intel_engine_cs, breadcrumbs);
        struct drm_i915_private *i915 = engine->i915;

        assert_spin_locked(&b->lock);
        if (b->rpm_wakelock)
                return;

        /* Since we are waiting on a request, the GPU should be busy
         * and should have its own rpm reference. For completeness,
         * record an rpm reference for ourselves to cover the
         * interrupt we unmask.
         */
        intel_runtime_pm_get_noresume(i915);
        b->rpm_wakelock = true;

        /* No interrupts? Kick the waiter every jiffie! */
        if (intel_irqs_enabled(i915)) {
                if (!test_bit(engine->id, &i915->gpu_error.test_irq_rings))
                        irq_enable(engine);
                b->irq_enabled = true;
        }

        if (!b->irq_enabled ||
            test_bit(engine->id, &i915->gpu_error.missed_irq_rings)) {
                mod_timer(&b->fake_irq, jiffies + 1);
        } else {
                /* Ensure we never sleep indefinitely */
                GEM_BUG_ON(!time_after(b->timeout, jiffies));
                mod_timer(&b->hangcheck, b->timeout);
        }
}

static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
{
        struct intel_engine_cs *engine =
                container_of(b, struct intel_engine_cs, breadcrumbs);

        assert_spin_locked(&b->lock);
        if (!b->rpm_wakelock)
                return;

        if (b->irq_enabled) {
                irq_disable(engine);
                b->irq_enabled = false;
        }

        intel_runtime_pm_put(engine->i915);
        b->rpm_wakelock = false;
}

static inline struct intel_wait *to_wait(struct rb_node *node)
{
        return container_of(node, struct intel_wait, node);
}

static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
                                              struct intel_wait *wait)
{
        assert_spin_locked(&b->lock);

        /* This request is completed, so remove it from the tree, mark it as
         * complete, and *then* wake up the associated task.
         */
        rb_erase(&wait->node, &b->waiters);
        RB_CLEAR_NODE(&wait->node);

        wake_up_process(wait->tsk); /* implicit smp_wmb() */
}

static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
                                    struct intel_wait *wait)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
        struct rb_node **p, *parent, *completed;
        bool first;
        u32 seqno;

        /* Insert the request into the retirement ordered list
         * of waiters by walking the rbtree. If we are the oldest
         * seqno in the tree (the first to be retired), then
         * set ourselves as the bottom-half.
         *
         * As we descend the tree, prune completed branches since we hold the
         * spinlock we know that the first_waiter must be delayed and can
         * reduce some of the sequential wake up latency if we take action
         * ourselves and wake up the completed tasks in parallel. Also, by
         * removing stale elements in the tree, we may be able to reduce the
         * ping-pong between the old bottom-half and ourselves as first-waiter.
         */
        first = true;
        parent = NULL;
        completed = NULL;
        seqno = intel_engine_get_seqno(engine);

         /* If the request completed before we managed to grab the spinlock,
          * return now before adding ourselves to the rbtree. We let the
          * current bottom-half handle any pending wakeups and instead
          * try and get out of the way quickly.
          */
        if (i915_seqno_passed(seqno, wait->seqno)) {
                RB_CLEAR_NODE(&wait->node);
                return first;
        }

        p = &b->waiters.rb_node;
        while (*p) {
                parent = *p;
                if (wait->seqno == to_wait(parent)->seqno) {
                        /* We have multiple waiters on the same seqno, select
                         * the highest priority task (that with the smallest
                         * task->prio) to serve as the bottom-half for this
                         * group.
                         */
                        if (wait->tsk->prio > to_wait(parent)->tsk->prio) {
                                p = &parent->rb_right;
                                first = false;
                        } else {
                                p = &parent->rb_left;
                        }
                } else if (i915_seqno_passed(wait->seqno,
                                             to_wait(parent)->seqno)) {
                        p = &parent->rb_right;
                        if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
                                completed = parent;
                        else
                                first = false;
                } else {
                        p = &parent->rb_left;
                }
        }
        rb_link_node(&wait->node, parent, p);
        rb_insert_color(&wait->node, &b->waiters);
        GEM_BUG_ON(!first && !rcu_access_pointer(b->irq_seqno_bh));

        if (completed) {
                struct rb_node *next = rb_next(completed);

                GEM_BUG_ON(!next && !first);
                if (next && next != &wait->node) {
                        GEM_BUG_ON(first);
                        b->timeout = wait_timeout();
                        b->first_wait = to_wait(next);
                        rcu_assign_pointer(b->irq_seqno_bh, b->first_wait->tsk);
                        /* As there is a delay between reading the current
                         * seqno, processing the completed tasks and selecting
                         * the next waiter, we may have missed the interrupt
                         * and so need for the next bottom-half to wakeup.
                         *
                         * Also as we enable the IRQ, we may miss the
                         * interrupt for that seqno, so we have to wake up
                         * the next bottom-half in order to do a coherent check
                         * in case the seqno passed.
                         */
                        __intel_breadcrumbs_enable_irq(b);
                        if (READ_ONCE(b->irq_posted))
                                wake_up_process(to_wait(next)->tsk);
                }

                do {
                        struct intel_wait *crumb = to_wait(completed);
                        completed = rb_prev(completed);
                        __intel_breadcrumbs_finish(b, crumb);
                } while (completed);
        }

        if (first) {
                GEM_BUG_ON(rb_first(&b->waiters) != &wait->node);
                b->timeout = wait_timeout();
                b->first_wait = wait;
                rcu_assign_pointer(b->irq_seqno_bh, wait->tsk);
                /* After assigning ourselves as the new bottom-half, we must
                 * perform a cursory check to prevent a missed interrupt.
                 * Either we miss the interrupt whilst programming the hardware,
                 * or if there was a previous waiter (for a later seqno) they
                 * may be woken instead of us (due to the inherent race
                 * in the unlocked read of b->irq_seqno_bh in the irq handler)
                 * and so we miss the wake up.
                 */
                __intel_breadcrumbs_enable_irq(b);
        }
        GEM_BUG_ON(!rcu_access_pointer(b->irq_seqno_bh));
        GEM_BUG_ON(!b->first_wait);
        GEM_BUG_ON(rb_first(&b->waiters) != &b->first_wait->node);

        return first;
}

bool intel_engine_add_wait(struct intel_engine_cs *engine,
                           struct intel_wait *wait)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
        bool first;

        spin_lock(&b->lock);
        first = __intel_engine_add_wait(engine, wait);
        spin_unlock(&b->lock);

        return first;
}

static inline bool chain_wakeup(struct rb_node *rb, int priority)
{
        return rb && to_wait(rb)->tsk->prio <= priority;
}

static inline int wakeup_priority(struct intel_breadcrumbs *b,
                                  struct task_struct *tsk)
{
        if (tsk == b->signaler)
                return INT_MIN;
        else
                return tsk->prio;
}

void intel_engine_remove_wait(struct intel_engine_cs *engine,
                              struct intel_wait *wait)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;

        /* Quick check to see if this waiter was already decoupled from
         * the tree by the bottom-half to avoid contention on the spinlock
         * by the herd.
         */
        if (RB_EMPTY_NODE(&wait->node))
                return;

        spin_lock(&b->lock);

        if (RB_EMPTY_NODE(&wait->node))
                goto out_unlock;

        if (b->first_wait == wait) {
                const int priority = wakeup_priority(b, wait->tsk);
                struct rb_node *next;

                GEM_BUG_ON(rcu_access_pointer(b->irq_seqno_bh) != wait->tsk);

                /* We are the current bottom-half. Find the next candidate,
                 * the first waiter in the queue on the remaining oldest
                 * request. As multiple seqnos may complete in the time it
                 * takes us to wake up and find the next waiter, we have to
                 * wake up that waiter for it to perform its own coherent
                 * completion check.
                 */
                next = rb_next(&wait->node);
                if (chain_wakeup(next, priority)) {
                        /* If the next waiter is already complete,
                         * wake it up and continue onto the next waiter. So
                         * if have a small herd, they will wake up in parallel
                         * rather than sequentially, which should reduce
                         * the overall latency in waking all the completed
                         * clients.
                         *
                         * However, waking up a chain adds extra latency to
                         * the first_waiter. This is undesirable if that
                         * waiter is a high priority task.
                         */
                        u32 seqno = intel_engine_get_seqno(engine);

                        while (i915_seqno_passed(seqno, to_wait(next)->seqno)) {
                                struct rb_node *n = rb_next(next);

                                __intel_breadcrumbs_finish(b, to_wait(next));
                                next = n;
                                if (!chain_wakeup(next, priority))
                                        break;
                        }
                }

                if (next) {
                        /* In our haste, we may have completed the first waiter
                         * before we enabled the interrupt. Do so now as we
                         * have a second waiter for a future seqno. Afterwards,
                         * we have to wake up that waiter in case we missed
                         * the interrupt, or if we have to handle an
                         * exception rather than a seqno completion.
                         */
                        b->timeout = wait_timeout();
                        b->first_wait = to_wait(next);
                        rcu_assign_pointer(b->irq_seqno_bh, b->first_wait->tsk);
                        if (b->first_wait->seqno != wait->seqno)
                                __intel_breadcrumbs_enable_irq(b);
                        wake_up_process(b->first_wait->tsk);
                } else {
                        b->first_wait = NULL;
                        rcu_assign_pointer(b->irq_seqno_bh, NULL);
                        __intel_breadcrumbs_disable_irq(b);
                }
        } else {
                GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
        }

        GEM_BUG_ON(RB_EMPTY_NODE(&wait->node));
        rb_erase(&wait->node, &b->waiters);

out_unlock:
        GEM_BUG_ON(b->first_wait == wait);
        GEM_BUG_ON(rb_first(&b->waiters) !=
                   (b->first_wait ? &b->first_wait->node : NULL));
        GEM_BUG_ON(!rcu_access_pointer(b->irq_seqno_bh) ^ RB_EMPTY_ROOT(&b->waiters));
        spin_unlock(&b->lock);
}

static bool signal_complete(struct drm_i915_gem_request *request)
{
        if (!request)
                return false;

        /* If another process served as the bottom-half it may have already
         * signalled that this wait is already completed.
         */
        if (intel_wait_complete(&request->signaling.wait))
                return true;

        /* Carefully check if the request is complete, giving time for the
         * seqno to be visible or if the GPU hung.
         */
        if (__i915_request_irq_complete(request))
                return true;

        return false;
}

static struct drm_i915_gem_request *to_signaler(struct rb_node *rb)
{
        return container_of(rb, struct drm_i915_gem_request, signaling.node);
}

static void signaler_set_rtpriority(void)
{
         struct sched_param param = { .sched_priority = 1 };

         sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
}

static int intel_breadcrumbs_signaler(void *arg)
{
        struct intel_engine_cs *engine = arg;
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
        struct drm_i915_gem_request *request;

        /* Install ourselves with high priority to reduce signalling latency */
        signaler_set_rtpriority();

        do {
                set_current_state(TASK_INTERRUPTIBLE);

                /* We are either woken up by the interrupt bottom-half,
                 * or by a client adding a new signaller. In both cases,
                 * the GPU seqno may have advanced beyond our oldest signal.
                 * If it has, propagate the signal, remove the waiter and
                 * check again with the next oldest signal. Otherwise we
                 * need to wait for a new interrupt from the GPU or for
                 * a new client.
                 */
                request = READ_ONCE(b->first_signal);
                if (signal_complete(request)) {
                        /* Wake up all other completed waiters and select the
                         * next bottom-half for the next user interrupt.
                         */
                        intel_engine_remove_wait(engine,
                                                 &request->signaling.wait);

                        local_bh_disable();
                        fence_signal(&request->fence);
                        local_bh_enable(); /* kick start the tasklets */

                        /* Find the next oldest signal. Note that as we have
                         * not been holding the lock, another client may
                         * have installed an even older signal than the one
                         * we just completed - so double check we are still
                         * the oldest before picking the next one.
                         */
                        spin_lock(&b->lock);
                        if (request == b->first_signal) {
                                struct rb_node *rb =
                                        rb_next(&request->signaling.node);
                                b->first_signal = rb ? to_signaler(rb) : NULL;
                        }
                        rb_erase(&request->signaling.node, &b->signals);
                        spin_unlock(&b->lock);

                        i915_gem_request_put(request);
                } else {
                        if (kthread_should_stop())
                                break;

                        schedule();
                }
        } while (1);
        __set_current_state(TASK_RUNNING);

        return 0;
}

void intel_engine_enable_signaling(struct drm_i915_gem_request *request)
{
        struct intel_engine_cs *engine = request->engine;
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
        struct rb_node *parent, **p;
        bool first, wakeup;

        /* locked by fence_enable_sw_signaling() */
        assert_spin_locked(&request->lock);

        request->signaling.wait.tsk = b->signaler;
        request->signaling.wait.seqno = request->fence.seqno;
        i915_gem_request_get(request);

        spin_lock(&b->lock);

        /* First add ourselves into the list of waiters, but register our
         * bottom-half as the signaller thread. As per usual, only the oldest
         * waiter (not just signaller) is tasked as the bottom-half waking
         * up all completed waiters after the user interrupt.
         *
         * If we are the oldest waiter, enable the irq (after which we
         * must double check that the seqno did not complete).
         */
        wakeup = __intel_engine_add_wait(engine, &request->signaling.wait);

        /* Now insert ourselves into the retirement ordered list of signals
         * on this engine. We track the oldest seqno as that will be the
         * first signal to complete.
         */
        parent = NULL;
        first = true;
        p = &b->signals.rb_node;
        while (*p) {
                parent = *p;
                if (i915_seqno_passed(request->fence.seqno,
                                      to_signaler(parent)->fence.seqno)) {
                        p = &parent->rb_right;
                        first = false;
                } else {
                        p = &parent->rb_left;
                }
        }
        rb_link_node(&request->signaling.node, parent, p);
        rb_insert_color(&request->signaling.node, &b->signals);
        if (first)
                smp_store_mb(b->first_signal, request);

        spin_unlock(&b->lock);

        if (wakeup)
                wake_up_process(b->signaler);
}

int intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
        struct task_struct *tsk;

        spin_lock_init(&b->lock);
        setup_timer(&b->fake_irq,
                    intel_breadcrumbs_fake_irq,
                    (unsigned long)engine);
        setup_timer(&b->hangcheck,
                    intel_breadcrumbs_hangcheck,
                    (unsigned long)engine);

        /* Spawn a thread to provide a common bottom-half for all signals.
         * As this is an asynchronous interface we cannot steal the current
         * task for handling the bottom-half to the user interrupt, therefore
         * we create a thread to do the coherent seqno dance after the
         * interrupt and then signal the waitqueue (via the dma-buf/fence).
         */
        tsk = kthread_run(intel_breadcrumbs_signaler, engine,
                          "i915/signal:%d", engine->id);
        if (IS_ERR(tsk))
                return PTR_ERR(tsk);

        b->signaler = tsk;

        return 0;
}

static void cancel_fake_irq(struct intel_engine_cs *engine)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;

        del_timer_sync(&b->hangcheck);
        del_timer_sync(&b->fake_irq);
        clear_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
}

void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;

        cancel_fake_irq(engine);
        spin_lock(&b->lock);

        __intel_breadcrumbs_disable_irq(b);
        if (intel_engine_has_waiter(engine)) {
                b->timeout = wait_timeout();
                __intel_breadcrumbs_enable_irq(b);
                if (READ_ONCE(b->irq_posted))
                        wake_up_process(b->first_wait->tsk);
        } else {
                /* sanitize the IMR and unmask any auxiliary interrupts */
                irq_disable(engine);
        }

        spin_unlock(&b->lock);
}

void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
{
        struct intel_breadcrumbs *b = &engine->breadcrumbs;

        if (!IS_ERR_OR_NULL(b->signaler))
                kthread_stop(b->signaler);

        cancel_fake_irq(engine);
}

unsigned int intel_kick_waiters(struct drm_i915_private *i915)
{
        struct intel_engine_cs *engine;
        unsigned int mask = 0;

        /* To avoid the task_struct disappearing beneath us as we wake up
         * the process, we must first inspect the task_struct->state under the
         * RCU lock, i.e. as we call wake_up_process() we must be holding the
         * rcu_read_lock().
         */
        for_each_engine(engine, i915)
                if (unlikely(intel_engine_wakeup(engine)))
                        mask |= intel_engine_flag(engine);

        return mask;
}

unsigned int intel_kick_signalers(struct drm_i915_private *i915)
{
        struct intel_engine_cs *engine;
        unsigned int mask = 0;

        for_each_engine(engine, i915) {
                if (unlikely(READ_ONCE(engine->breadcrumbs.first_signal))) {
                        wake_up_process(engine->breadcrumbs.signaler);
                        mask |= intel_engine_flag(engine);
                }
        }

        return mask;
}