drm/i915: use semaphores for the display plane

In theory this will have performance and power improvements. Performance
because we don't need to stall when the scanout BO is busy, and power
because we don't have to stall when the BO is busy (and the ring can
even go to sleep if the HW supports it).

v2:
squash 2 patches into 1 (me)
un-inline the enable_semaphores function (Daniel)
remove comment about SNB hangs from i915_gem_object_sync (Chris)
rename intel_enable_semaphores to i915_semaphore_is_enabled (me)
removed page flip comment; "no why" (Chris)

To address other comments from Daniel (irc):
update the comment to say 'vt-d is crap, don't enable semaphores'
  - I think you misinterpreted Chris' comment, it already exists.
checking out whether we can pageflip on the render ring on ivb (didn't
work on early silicon)
  - We don't want to enable workarounds for early silicon unless we have
    to.
  - I can't find any references in the docs about this.
optionally use it if the fb is already busy on the render ring
  - This should be how the code already worked, unless I am
    misunderstanding your meaning.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 1 insertions, 59 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 56d1001..2a24d0c 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -835,64 +835,6 @@ i915_gem_execbuffer_flush(struct drm_device *dev,
 	return 0;
 }
 
-static bool
-intel_enable_semaphores(struct drm_device *dev)
-{
-	if (INTEL_INFO(dev)->gen < 6)
-		return 0;
-
-	if (i915_semaphores >= 0)
-		return i915_semaphores;
-
-	/* Disable semaphores on SNB */
-	if (INTEL_INFO(dev)->gen == 6)
-		return 0;
-
-	return 1;
-}
-
-static int
-i915_gem_execbuffer_sync_rings(struct drm_i915_gem_object *obj,
-			       struct intel_ring_buffer *to)
-{
-	struct intel_ring_buffer *from = obj->ring;
-	u32 seqno;
-	int ret, idx;
-
-	if (from == NULL || to == from)
-		return 0;
-
-	/* XXX gpu semaphores are implicated in various hard hangs on SNB */
-	if (!intel_enable_semaphores(obj->base.dev))
-		return i915_gem_object_wait_rendering(obj);
-
-	idx = intel_ring_sync_index(from, to);
-
-	seqno = obj->last_rendering_seqno;
-	if (seqno <= from->sync_seqno[idx])
-		return 0;
-
-	if (seqno == from->outstanding_lazy_request) {
-		struct drm_i915_gem_request *request;
-
-		request = kzalloc(sizeof(*request), GFP_KERNEL);
-		if (request == NULL)
-			return -ENOMEM;
-
-		ret = i915_add_request(from, NULL, request);
-		if (ret) {
-			kfree(request);
-			return ret;
-		}
-
-		seqno = request->seqno;
-	}
-
-	from->sync_seqno[idx] = seqno;
-
-	return to->sync_to(to, from, seqno - 1);
-}
-
 static int
 i915_gem_execbuffer_wait_for_flips(struct intel_ring_buffer *ring, u32 flips)
 {
@@ -954,7 +896,7 @@ i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer *ring,
 	}
 
 	list_for_each_entry(obj, objects, exec_list) {
-		ret = i915_gem_execbuffer_sync_rings(obj, ring);
+		ret = i915_gem_object_sync(obj, ring);
 		if (ret)
 			return ret;
 	}