[Intel-gfx] [PATCH] drm/i915: Add a strong mb to resetting the has-CS-interrupt bit

[Chris Wilson]

After a reset, the state of the CSB registers are scrubbed and not valid
until a powercontext is reloaded. We only know when a powercontext has
been reloaded once we see a CS-interrupt, before then we must ignore the
CSB registers within the execlists_submission_tasklet. However, glk is
sporadically dying with an illegal CSB pointer value (both in the HSWP
and mmio) suggesting that it is running with the CS-interrupt bit set
before the powercontext has been reloaded. Make sure the clearing of
that bit is serialised on reset with the re-enabling of the tasklet.

References: https://bugs.freedesktop.org/show_bug.cgi?id=104262
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5b4cfb20de97..a68fc1240c95 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3089,7 +3089,11 @@ i915_gem_reset_request(struct intel_engine_cs *engine,
 void i915_gem_reset_engine(struct intel_engine_cs *engine,
 			   struct drm_i915_gem_request *request)
 {
-	engine->irq_posted = 0;
+	/*
+	 * Make sure this write is visible before we re-enable the interrupt
+	 * handlers on another CPU.
+	 */
+	smp_store_mb(engine->irq_posted, 0);
 
 	if (request)
 		request = i915_gem_reset_request(engine, request);
-- 
2.15.1