drm/i915/breadcrumbs: Keep the fake irq armed across reset

Instead of synchronously cancelling the timer and re-enabling it inside
the reset callbacks, keep the timer enabled and let it die on its next
wakeup if no longer required. This allows
intel_engine_reset_breadcrumbs() to be used from an atomic
(timer/softirq) context such as required for resetting an engine.

It also allows us to react better to the user poking around debugfs for
testing missed irqs.

v2: Tighten the order of del_timer_sync as the fake_irq timer
may trigger the hangcheck timer, and so we should cancel it first and
then cancel the hangcheck (Mika)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180424142945.6787-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 671a6d61e29da618c61f058f23afb9512903997a..5ce4f51232f5df83cc51494b28ac68ba08b08898 100644 (file)
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -130,11 +130,12 @@ static void intel_breadcrumbs_hangcheck(struct timer_list *t)
 
 static void intel_breadcrumbs_fake_irq(struct timer_list *t)
 {
-       struct intel_engine_cs *engine = from_timer(engine, t,
-                                                   breadcrumbs.fake_irq);
+       struct intel_engine_cs *engine =
+               from_timer(engine, t, breadcrumbs.fake_irq);
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
-       /* The timer persists in case we cannot enable interrupts,
+       /*
+        * The timer persists in case we cannot enable interrupts,
         * or if we have previously seen seqno/interrupt incoherency
         * ("missed interrupt" syndrome, better known as a "missed breadcrumb").
         * Here the worker will wake up every jiffie in order to kick the
@@ -148,6 +149,12 @@ static void intel_breadcrumbs_fake_irq(struct timer_list *t)
        if (!b->irq_armed)
                return;
 
+       /* If the user has disabled the fake-irq, restore the hangchecking */
+       if (!test_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings)) {
+               mod_timer(&b->hangcheck, wait_timeout());
+               return;
+       }
+
        mod_timer(&b->fake_irq, jiffies + 1);
 }
 
@@ -831,8 +838,8 @@ static void cancel_fake_irq(struct intel_engine_cs *engine)
 {
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
+       del_timer_sync(&b->fake_irq); /* may queue b->hangcheck */
        del_timer_sync(&b->hangcheck);
-       del_timer_sync(&b->fake_irq);
        clear_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
 }
 
@@ -840,15 +847,22 @@ void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
 {
        struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
-       cancel_fake_irq(engine);
        spin_lock_irq(&b->irq_lock);
 
+       /*
+        * Leave the fake_irq timer enabled (if it is running), but clear the
+        * bit so that it turns itself off on its next wake up and goes back
+        * to the long hangcheck interval if still required.
+        */
+       clear_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
+
        if (b->irq_enabled)
                irq_enable(engine);
        else
                irq_disable(engine);
 
-       /* We set the IRQ_BREADCRUMB bit when we enable the irq presuming the
+       /*
+        * We set the IRQ_BREADCRUMB bit when we enable the irq presuming the
         * GPU is active and may have already executed the MI_USER_INTERRUPT
         * before the CPU is ready to receive. However, the engine is currently
         * idle (we haven't started it yet), there is no possibility for a
@@ -857,9 +871,6 @@ void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
         */
        clear_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 
-       if (b->irq_armed)
-               enable_fake_irq(b);
-
        spin_unlock_irq(&b->irq_lock);
 }