[PATCH 2/6] drm/i915: Update the breadcrumb interrupt counter before enabling

[Chris Wilson]

In order to close a race with a long running hangcheck comparing a stale
interrupt counter with a just started waiter, we need to first bump the
counter as we start the fresh wait.

References: https://bugs.freedesktop.org/show_bug.cgi?id=96974
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index f0b56e3f4abe..d893ccdd62ac 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -51,6 +51,13 @@ static void irq_enable(struct intel_engine_cs *engine)
 	 */
 	engine->breadcrumbs.irq_posted = true;
 
+	/* Make sure the current hangcheck doesn't falsely accuse a just
+	 * started irq handler from missing an interrupt (because the
+	 * interrupt count still matches the stale value from when
+	 * the irq handler was disabled, many hangchecks ago).
+	 */
+	engine->breadcrumbs.irq_wakeups++;
+
 	spin_lock_irq(&engine->i915->irq_lock);
 	engine->irq_enable(engine);
 	spin_unlock_irq(&engine->i915->irq_lock);
-- 
2.8.1