[Intel-gfx] [PATCH v2] drm/i915: fix the dequeue logic for single_port_submission context

[Min He]

For a singl_port_submission context, it can only be submitted to port 0,
and there shouldn't be any other context in port 1 at the same time. This
is required by GVT-g context to have an opportunity to save/restore some
non-hw context render registers.
This patch is to implement the correct logic in execlists_dequeue.

V2: optimized code by following Chris's advice, and added more comments to
explain the patch.

Signed-off-by: Min He <min.he at intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index f50feaa..4f692a8 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -499,7 +499,8 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 			 * context (even though a different request) to
 			 * the second port.
 			 */
-			if (ctx_single_port_submission(cursor->ctx))
+			if (ctx_single_port_submission(cursor->ctx)
+				|| ctx_single_port_submission(last->ctx))
 				break;
 
 			GEM_BUG_ON(last->ctx == cursor->ctx);
-- 
1.9.1