drm/i915: Check for matching ringbuffer in logical_ring_wait_request()

The request queue is per-engine, and may therefore contain requests
from several different contexts/ringbuffers. In determining which
request to wait for, this function should only consider requests
from the ringbuffer that it's checking for space, and ignore any
that it finds that belong to other contexts.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -930,6 +930,16 @@ static int logical_ring_wait_request(struct intel_ringbuffer *ringbuf,
 	}
 
 	list_for_each_entry(request, &ring->request_list, list) {
+		/*
+		 * The request queue is per-engine, so can contain requests
+		 * from multiple ringbuffers. Here, we must ignore any that
+		 * aren't from the ringbuffer we're considering.
+		 */
+		struct intel_context *ctx = request->ctx;
+		if (ctx->engine[ring->id].ringbuf != ringbuf)
+			continue;
+
+		/* Would completion of this request free enough space? */
 		if (__intel_ring_space(request->tail, ringbuf->tail,
 				       ringbuf->size) >= bytes) {
 			seqno = request->seqno;