drm/i915/guc: Ensure request ordering via completion fences

If two requests are on the same ring, they are explicitly ordered by the
HW. So, a submission fence is sufficient to ensure ordering when using
the new GuC submission interface. Conversely, if two requests share a
timeline and are on the same physical engine but different context this
doesn't ensure ordering on the new GuC submission interface. So, a
completion fence needs to be used to ensure ordering.

v2:
 (Daniele)
  - Don't delete spin lock
v3:
 (Daniele)
  - Delete forward dec
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721215101.139794-13-matthew.brost@intel.com

drivers/gpu/drm/i915/i915_request.c

@@ -432,6 +432,7 @@ void i915_request_retire_upto(struct i915_request *rq)
 
 	do {
 		tmp = list_first_entry(&tl->requests, typeof(*tmp), link);
+		GEM_BUG_ON(!i915_request_completed(tmp));
 	} while (i915_request_retire(tmp) && tmp != rq);
 }
 
@@ -1463,7 +1464,8 @@ i915_request_await_request(struct i915_request *to, struct i915_request *from)
 			return ret;
 	}
 
-	if (is_power_of_2(to->execution_mask | READ_ONCE(from->execution_mask)))
+	if (!intel_engine_uses_guc(to->engine) &&
+	    is_power_of_2(to->execution_mask | READ_ONCE(from->execution_mask)))
 		ret = await_request_submit(to, from);
 	else
 		ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
@@ -1622,6 +1624,8 @@ __i915_request_add_to_timeline(struct i915_request *rq)
 	prev = to_request(__i915_active_fence_set(&timeline->last_request,
 						  &rq->fence));
 	if (prev && !__i915_request_is_complete(prev)) {
+		bool uses_guc = intel_engine_uses_guc(rq->engine);
+
 		/*
 		 * The requests are supposed to be kept in order. However,
 		 * we need to be wary in case the timeline->last_request
@@ -1632,7 +1636,9 @@ __i915_request_add_to_timeline(struct i915_request *rq)
 			   i915_seqno_passed(prev->fence.seqno,
 					     rq->fence.seqno));
 
-		if (is_power_of_2(READ_ONCE(prev->engine)->mask | rq->engine->mask))
+		if ((!uses_guc &&
+		     is_power_of_2(READ_ONCE(prev->engine)->mask | rq->engine->mask)) ||
+		    (uses_guc && prev->context == rq->context))
 			i915_sw_fence_await_sw_fence(&rq->submit,
 						     &prev->submit,
 						     &rq->submitq);