[Intel-gfx] [PATCH] drm/i915: Synchronize irq before parking each engine

[Chris Wilson]

When we park the engine (upon idling), we kill the irq tasklet. However,
to be sure that it is not restarted by a final interrupt after doing so,
flush the interrupt handler before parking. As we only park the engines
when we believe the system is idle, there should not be any spurious
interrupts later to distrub us; so flushing the final in-flight
interrupt should be sufficient.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bb0e85043e01..b547a6327d34 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3327,6 +3327,12 @@ i915_gem_idle_work_handler(struct work_struct *work)
 	if (new_requests_since_last_retire(dev_priv))
 		goto out_unlock;
 
+	/*
+	 * Be paranoid and flush a concurrent interrupt to make sure
+	 * we don't reactivate any irq tasklets after parking.
+	 */
+	synchronize_irq(dev_priv->drm.irq);
+
 	/*
 	 * We are committed now to parking the engines, make sure there
 	 * will be no more interrupts arriving later.
-- 
2.15.0.rc1