[Intel-gfx] [PATCH 05/13] drm/i915: Insert a flush between batches if the breadcrumb was dropped

[Chris Wilson]

If we drop the breadcrumb request after a batch due to a signal for
example we aim to fix it up at the next opportunity. In this case we
emit a second batchbuffer with no waits upon the first and so no
opportunity to insert the missing request, so we need to emit the
missing flush for coherency. (Note that that invalidating the render
cache is the same as flushing it, so there should have been no
observable corruption.)

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 50e83e5..c08229f 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -885,11 +885,16 @@ i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer *ring,
 			return ret;
 	}
 
-	/* Unconditionally invalidate gpu caches. */
-	ret = i915_gem_flush_ring(ring, I915_GEM_GPU_DOMAINS, 0);
+	/* Unconditionally invalidate gpu caches and ensure that we do flush
+	 * any residual writes from the previous batch.
+	 */
+	ret = i915_gem_flush_ring(ring,
+				  I915_GEM_GPU_DOMAINS,
+				  ring->gpu_caches_dirty ? I915_GEM_GPU_DOMAINS : 0);
 	if (ret)
 		return ret;
 
+	ring->gpu_caches_dirty = false;
 	return 0;
 }
 
-- 
1.7.10.4