drm/i915/guc: Add bypass tasklet submission path to GuC

Add bypass tasklet submission path to GuC. The tasklet is only used if H2G
channel has backpresure.
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721215101.139794-6-matthew.brost@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c

@@ -172,6 +172,12 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
 	return err;
 }
 
+static inline void guc_set_lrc_tail(struct i915_request *rq)
+{
+	rq->context->lrc_reg_state[CTX_RING_TAIL] =
+		intel_ring_set_tail(rq->ring, rq->tail);
+}
+
 static inline int rq_prio(const struct i915_request *rq)
 {
 	return rq->sched.attr.priority;
@@ -215,8 +221,7 @@ static int guc_dequeue_one_context(struct intel_guc *guc)
 	}
 done:
 	if (submit) {
-		last->context->lrc_reg_state[CTX_RING_TAIL] =
-			intel_ring_set_tail(last->ring, last->tail);
+		guc_set_lrc_tail(last);
 resubmit:
 		/*
 		 * We only check for -EBUSY here even though it is possible for
@@ -496,19 +501,35 @@ static inline void queue_request(struct i915_sched_engine *sched_engine,
 	set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
 }
 
+static int guc_bypass_tasklet_submit(struct intel_guc *guc,
+				     struct i915_request *rq)
+{
+	int ret;
+
+	__i915_request_submit(rq);
+
+	trace_i915_request_in(rq, 0);
+
+	guc_set_lrc_tail(rq);
+	ret = guc_add_request(guc, rq);
+	if (ret == -EBUSY)
+		guc->stalled_request = rq;
+
+	return ret;
+}
+
 static void guc_submit_request(struct i915_request *rq)
 {
 	struct i915_sched_engine *sched_engine = rq->engine->sched_engine;
+	struct intel_guc *guc = &rq->engine->gt->uc.guc;
 	unsigned long flags;
 
 	/* Will be called from irq-context when using foreign fences. */
 	spin_lock_irqsave(&sched_engine->lock, flags);
 
+	if (guc->stalled_request || !i915_sched_engine_is_empty(sched_engine))
 		queue_request(sched_engine, rq, rq_prio(rq));
-
-	GEM_BUG_ON(i915_sched_engine_is_empty(sched_engine));
-	GEM_BUG_ON(list_empty(&rq->sched.link));
-
+	else if (guc_bypass_tasklet_submit(guc, rq) == -EBUSY)
 		tasklet_hi_schedule(&sched_engine->tasklet);
 
 	spin_unlock_irqrestore(&sched_engine->lock, flags);