[PATCH 02/29] drm/i915: Lift timeline ordering to await_dma_fence

[Chris Wilson]

Currently we filter out repeated use of the same timeline in the low
level i915_gem_request_await_request(), after having added the
dependency on the old request. However, we can lift this to
i915_gem_request_await_dma_fence() (before the dependency is added)
using the observation that requests along the same timeline are
explicitly ordered via i915_add_request (along with the dependencies).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_request.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 313cdff7c6dd..31874a38752e 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -663,6 +663,7 @@ i915_gem_request_await_request(struct drm_i915_gem_request *to,
 	int ret;
 
 	GEM_BUG_ON(to == from);
+	GEM_BUG_ON(to->timeline == from->timeline);
 
 	if (to->engine->schedule) {
 		ret = i915_priotree_add_dependency(to->i915,
@@ -672,9 +673,6 @@ i915_gem_request_await_request(struct drm_i915_gem_request *to,
 			return ret;
 	}
 
-	if (to->timeline == from->timeline)
-		return 0;
-
 	if (to->engine == from->engine) {
 		ret = i915_sw_fence_await_sw_fence_gfp(&to->submit,
 						       &from->submit,
@@ -723,6 +721,13 @@ i915_gem_request_await_dma_fence(struct drm_i915_gem_request *req,
 	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
 		return 0;
 
+	/* Requests on the same timeline are explicitly ordered, along with
+	 * their dependencies, by i915_add_request() which ensures that requests
+	 * are submitted in-order through each ring.
+	 */
+	if (fence->context == req->fence.context)
+		return 0;
+
 	if (dma_fence_is_i915(fence))
 		return i915_gem_request_await_request(req, to_request(fence));
 
-- 
2.11.0