[Intel-gfx] [PATCH 09/10] drm/i915/bdw: poll semaphores

[Rodrigo Vivi]

From: Ben Widawsky <benjamin.widawsky at intel.com>

As Ville points out, it's possible/probable we don't actually need this.
Potentially, this validates the letter of the spec, and not the spirit.

Ville:
> I discussed this on irc w/ Ben, and I was suggesting we don't need to
> poll. Polling apparently can be used as a workaround for certain
> hardware issues, but it looks like those issues shouldn't affect us,
> for the momemnt at least. So my suggestion was to try w/o polling
> first (since there could be some power cost to polling) and add the
> poll bit if problems arise.

Rodrigo: Spec suggests this as an W/A for GT3. However semaphores didn't
worked in my BDW GT2 on Signal Mode. So pool mode is definitely needed.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Tested-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 2e0413c..7a6112e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -847,6 +847,7 @@ gen8_ring_sync(struct intel_engine_cs *waiter,
 
 	intel_ring_emit(waiter, MI_SEMAPHORE_WAIT |
 				MI_SEMAPHORE_GLOBAL_GTT |
+				MI_SEMAPHORE_POLL |
 				MI_SEMAPHORE_SAD_GTE_SDD);
 	intel_ring_emit(waiter, seqno);
 	intel_ring_emit(waiter,
-- 
1.9.3