drm/i915: Remove the now redundant 'obj->ring'

The ring member of the object structure was always updated with the
last_read_seqno member. Thus with the conversion to last_read_req, obj->ring is
now a direct copy of obj->last_read_req->ring. This makes it somewhat redundant
and potentially misleading (especially as there was no comment to explain its
purpose).

This checkin removes the redundant field. Many uses were simply testing for
non-null to see if the object is active on the GPU. Some of these have been
converted to check 'obj->active' instead. Others (where the last_read_req is
about to be used anyway) have been changed to check obj->last_read_req. The rest
simply pull the ring out from the request structure and proceed as before.

For: VIZ-4377
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Thomas Daniel <Thomas.Daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 16a8445..b9222a7 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2263,14 +2263,18 @@
 i915_gem_object_move_to_active(struct drm_i915_gem_object *obj,
 			       struct intel_engine_cs *ring)
 {
-	struct drm_i915_gem_request *req = intel_ring_get_request(ring);
+	struct drm_i915_gem_request *req;
+	struct intel_engine_cs *old_ring;
 
 	BUG_ON(ring == NULL);
-	if (obj->ring != ring && obj->last_write_req) {
+
+	req = intel_ring_get_request(ring);
+	old_ring = i915_gem_request_get_ring(obj->last_read_req);
+
+	if (old_ring != ring && obj->last_write_req) {
 		/* Keep the request relative to the current ring */
 		i915_gem_request_assign(&obj->last_write_req, req);
 	}
-	obj->ring = ring;
 
 	/* Add a reference if we're newly entering the active list. */
 	if (!obj->active) {
@@ -2309,7 +2313,6 @@
 	intel_fb_obj_flush(obj, true);
 
 	list_del_init(&obj->ring_list);
-	obj->ring = NULL;
 
 	i915_gem_request_assign(&obj->last_read_req, NULL);
 	i915_gem_request_assign(&obj->last_write_req, NULL);
@@ -2326,9 +2329,7 @@
 static void
 i915_gem_object_retire(struct drm_i915_gem_object *obj)
 {
-	struct intel_engine_cs *ring = obj->ring;
-
-	if (ring == NULL)
+	if (obj->last_read_req == NULL)
 		return;
 
 	if (i915_gem_request_completed(obj->last_read_req, true))
@@ -2861,14 +2862,17 @@
 static int
 i915_gem_object_flush_active(struct drm_i915_gem_object *obj)
 {
+	struct intel_engine_cs *ring;
 	int ret;
 
 	if (obj->active) {
+		ring = i915_gem_request_get_ring(obj->last_read_req);
+
 		ret = i915_gem_check_olr(obj->last_read_req);
 		if (ret)
 			return ret;
 
-		i915_gem_retire_requests_ring(obj->ring);
+		i915_gem_retire_requests_ring(ring);
 	}
 
 	return 0;
@@ -2971,10 +2975,12 @@
 i915_gem_object_sync(struct drm_i915_gem_object *obj,
 		     struct intel_engine_cs *to)
 {
-	struct intel_engine_cs *from = obj->ring;
+	struct intel_engine_cs *from;
 	u32 seqno;
 	int ret, idx;
 
+	from = i915_gem_request_get_ring(obj->last_read_req);
+
 	if (from == NULL || to == from)
 		return 0;
 
@@ -3929,7 +3935,7 @@
 	bool was_pin_display;
 	int ret;
 
-	if (pipelined != obj->ring) {
+	if (pipelined != i915_gem_request_get_ring(obj->last_read_req)) {
 		ret = i915_gem_object_sync(obj, pipelined);
 		if (ret)
 			return ret;
@@ -4284,9 +4290,11 @@
 	ret = i915_gem_object_flush_active(obj);
 
 	args->busy = obj->active;
-	if (obj->ring) {
+	if (obj->last_read_req) {
+		struct intel_engine_cs *ring;
 		BUILD_BUG_ON(I915_NUM_RINGS > 16);
-		args->busy |= intel_ring_flag(obj->ring) << 16;
+		ring = i915_gem_request_get_ring(obj->last_read_req);
+		args->busy |= intel_ring_flag(ring) << 16;
 	}
 
 	drm_gem_object_unreference(&obj->base);