drm/i915/guc: drop cached copy of 'wq_head'

Now that we keep the GuC client process descriptor permanently mapped,
we don't really need to keep a local copy of the GuC's work-queue-head.
So we can simplify the code a little by not doing this.
Signed-off-by: Alex Dai <yu.dai@intel.com>
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -238,9 +238,6 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
 			db_exc.cookie = 1;
 	}
 
-	/* Finally, update the cached copy of the GuC's WQ head */
-	gc->wq_head = desc->head;
-
 	return ret;
 }
 
@@ -465,17 +462,10 @@ int i915_guc_wq_check_space(struct i915_guc_client *gc)
 	if (!gc)
 		return 0;
 
-	/* Quickly return if wq space is available since last time we cache the
-	 * head position. */
-	if (CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size) >= size)
-		return 0;
-
 	desc = gc->client_base + gc->proc_desc_offset;
 
 	while (timeout_counter-- > 0) {
-		gc->wq_head = desc->head;
-
-		if (CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size) >= size) {
+		if (CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size) >= size) {
 			ret = 0;
 			break;
 		}
@@ -490,11 +480,13 @@ int i915_guc_wq_check_space(struct i915_guc_client *gc)
 static int guc_add_workqueue_item(struct i915_guc_client *gc,
 				  struct drm_i915_gem_request *rq)
 {
+	struct guc_process_desc *desc;
 	struct guc_wq_item *wqi;
 	void *base;
 	u32 tail, wq_len, wq_off, space;
 
-	space = CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size);
+	desc = gc->client_base + gc->proc_desc_offset;
+	space = CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size);
 	if (WARN_ON(space < sizeof(struct guc_wq_item)))
 		return -ENOSPC; /* shouldn't happen */
 

drivers/gpu/drm/i915/intel_guc.h

@@ -46,7 +46,7 @@ struct i915_guc_client {
 	uint32_t wq_offset;
 	uint32_t wq_size;
 	uint32_t wq_tail;
-	uint32_t wq_head;
+	uint32_t unused;		/* Was 'wq_head'		*/
 
 	/* GuC submission statistics & status */
 	uint64_t submissions[GUC_MAX_ENGINES_NUM];