drm/i915: Defer transfer onto execution timeline to actual hw submission

Defer the transfer from the client's timeline onto the execution
timeline from the point of readiness to the point of actual submission.
For example, in execlists, a request is finally submitted to hardware
when the hardware is ready, and only put onto the hardware queue when
the request is ready. By deferring the transfer, we ensure that the
timeline is maintained in retirement order if we decide to queue the
requests onto the hardware in a different order than fifo.

v2: Rebased onto distinct global/user timeline lock classes.
v3: Play with the position of the spin_lock().
v4: Nesting finally resolved with distinct sw_fence lock classes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161114204105.29171-4-chris@chris-wilson.co.uk

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 666dab7a675a..942f5000d372 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -629,11 +629,23 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
 static void i915_guc_submit(struct drm_i915_gem_request *rq)
 {
 	struct drm_i915_private *dev_priv = rq->i915;
-	unsigned int engine_id = rq->engine->id;
+	struct intel_engine_cs *engine = rq->engine;
+	unsigned int engine_id = engine->id;
 	struct intel_guc *guc = &rq->i915->guc;
 	struct i915_guc_client *client = guc->execbuf_client;
 	int b_ret;
 
+	/* We keep the previous context alive until we retire the following
+	 * request. This ensures that any the context object is still pinned
+	 * for any residual writes the HW makes into it on the context switch
+	 * into the next object following the breadcrumb. Otherwise, we may
+	 * retire the context too early.
+	 */
+	rq->previous_context = engine->last_context;
+	engine->last_context = rq->ctx;
+
+	i915_gem_request_submit(rq);
+
 	spin_lock(&client->wq_lock);
 	guc_wq_item_append(client, rq);