[Intel-gfx] [PATCH] drm/i915/guc: make forwarding of VBlanks conditional

[Dave Gordon]

Apparently we shouldn't forward VBlanks to the GuC unconditionally,
as it may trigger a race condition in the GuC's internal dispatcher.

>From an internal message from Harsh Chheda <harsh.j.chheda at intel.com>
>
> If the context has switched out the [GuC] scheduler should know so
> that it can  put the context in wait state and schedule something
> else.  If the context which is waiting on Vblank is still on the CS
> then [the GuC] scheduler does not need to know. If in this case wait
> on Vblank is sent to Guc while the context is still on CS there is
> an edge condition when the Vblank may get satisfied right after
> sending interrupt to guc and context may complete. Scheduler will
> then incorrectly mark the context to be in wait state.

So we need to change this register setting to GFX_FORWARD_VBLANK_COND.

Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
Cc: Harsh Chheda <harsh.j.chheda at intel.com>
---
 drivers/gpu/drm/i915/intel_guc_loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_guc_loader.c b/drivers/gpu/drm/i915/intel_guc_loader.c
index 8fe96a2..af9f51e 100644
--- a/drivers/gpu/drm/i915/intel_guc_loader.c
+++ b/drivers/gpu/drm/i915/intel_guc_loader.c
@@ -106,7 +106,7 @@ static void direct_interrupts_to_guc(struct drm_i915_private *dev_priv)
 	u32 tmp;
 
 	/* tell all command streamers to forward interrupts and vblank to GuC */
-	irqs = _MASKED_FIELD(GFX_FORWARD_VBLANK_MASK, GFX_FORWARD_VBLANK_ALWAYS);
+	irqs = _MASKED_FIELD(GFX_FORWARD_VBLANK_MASK, GFX_FORWARD_VBLANK_COND);
 	irqs |= _MASKED_BIT_ENABLE(GFX_INTERRUPT_STEERING);
 	for_each_engine(engine, dev_priv)
 		I915_WRITE(RING_MODE_GEN7(engine), irqs);
-- 
1.9.1