[Intel-gfx] [PATCH 3/6] drm/i915: Don't emit semaphore wait if wrap happened

[Mika Kuoppala]

If wrap just happened we need to prevent emitting waits for
pre wrap values. Detect this and emit no-ops instead.

v2: Use olr > seqno to detect wrap instead of *seqno == 0
as suggested by Chris Wilson.

Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c |   21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 36e1e13a..2305af5 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -626,11 +626,22 @@ gen6_ring_sync(struct intel_ring_buffer *waiter,
 	if (ret)
 		return ret;
 
-	intel_ring_emit(waiter,
-			dw1 | signaller->semaphore_register[waiter->id]);
-	intel_ring_emit(waiter, seqno);
-	intel_ring_emit(waiter, 0);
-	intel_ring_emit(waiter, MI_NOOP);
+	BUG_ON(!waiter->outstanding_lazy_request);
+
+	/* If seqno wrap happened, omit the wait with no-ops */
+	if (likely(waiter->outstanding_lazy_request > seqno)) {
+		intel_ring_emit(waiter,
+				dw1 |
+				signaller->semaphore_register[waiter->id]);
+		intel_ring_emit(waiter, seqno);
+		intel_ring_emit(waiter, 0);
+		intel_ring_emit(waiter, MI_NOOP);
+	} else {
+		intel_ring_emit(waiter, MI_NOOP);
+		intel_ring_emit(waiter, MI_NOOP);
+		intel_ring_emit(waiter, MI_NOOP);
+		intel_ring_emit(waiter, MI_NOOP);
+	}
 	intel_ring_advance(waiter);
 
 	return 0;
-- 
1.7.9.5