drm/i915/guc: Prepare for nonblocking execbuf submission

Currently the presumption is that the request construction and its
submission to the GuC are all under the same holding of struct_mutex. We
wish to relax this to separate the request construction and the later
submission to the GuC. This requires us to reserve some space in the
GuC command queue for the future submission. For flexibility to handle
out-of-order request submission we do not preallocate the next slot in
the GuC command queue during request construction, just ensuring that
there is enough space later.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20160909131201.16673-17-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -432,20 +432,23 @@ int i915_guc_wq_check_space(struct drm_i915_gem_request *request)
 {
 	const size_t wqi_size = sizeof(struct guc_wq_item);
 	struct i915_guc_client *gc = request->i915->guc.execbuf_client;
-	struct guc_process_desc *desc;
+	struct guc_process_desc *desc = gc->client_base + gc->proc_desc_offset;
 	u32 freespace;
+	int ret;
 
-	GEM_BUG_ON(gc == NULL);
-
-	desc = gc->client_base + gc->proc_desc_offset;
-
+	spin_lock(&gc->wq_lock);
 	freespace = CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size);
-	if (likely(freespace >= wqi_size))
-		return 0;
-
-	gc->no_wq_space += 1;
+	freespace -= gc->wq_rsvd;
+	if (likely(freespace >= wqi_size)) {
+		gc->wq_rsvd += wqi_size;
+		ret = 0;
+	} else {
+		gc->no_wq_space++;
+		ret = -EAGAIN;
+	}
+	spin_unlock(&gc->wq_lock);
 
-	return -EAGAIN;
+	return ret;
 }
 
 static void guc_add_workqueue_item(struct i915_guc_client *gc,
@@ -480,12 +483,14 @@ static void guc_add_workqueue_item(struct i915_guc_client *gc,
 	 * workqueue buffer dw by dw.
 	 */
 	BUILD_BUG_ON(wqi_size != 16);
+	GEM_BUG_ON(gc->wq_rsvd < wqi_size);
 
 	/* postincrement WQ tail for next time */
 	wq_off = gc->wq_tail;
+	GEM_BUG_ON(wq_off & (wqi_size - 1));
 	gc->wq_tail += wqi_size;
 	gc->wq_tail &= gc->wq_size - 1;
-	GEM_BUG_ON(wq_off & (wqi_size - 1));
+	gc->wq_rsvd -= wqi_size;
 
 	/* WQ starts from the page after doorbell / process_desc */
 	wq_page = (wq_off + GUC_DB_SIZE) >> PAGE_SHIFT;
@@ -589,6 +594,7 @@ static void i915_guc_submit(struct drm_i915_gem_request *rq)
 	struct i915_guc_client *client = guc->execbuf_client;
 	int b_ret;
 
+	spin_lock(&client->wq_lock);
 	guc_add_workqueue_item(client, rq);
 	b_ret = guc_ring_doorbell(client);
 
@@ -599,6 +605,7 @@ static void i915_guc_submit(struct drm_i915_gem_request *rq)
 
 	guc->submissions[engine_id] += 1;
 	guc->last_seqno[engine_id] = rq->fence.seqno;
+	spin_unlock(&client->wq_lock);
 }
 
 /*
@@ -789,6 +796,8 @@ guc_client_alloc(struct drm_i915_private *dev_priv,
 	/* We'll keep just the first (doorbell/proc) page permanently kmap'd. */
 	client->vma = vma;
 	client->client_base = kmap(i915_vma_first_page(vma));
+
+	spin_lock_init(&client->wq_lock);
 	client->wq_offset = GUC_DB_SIZE;
 	client->wq_size = GUC_WQ_SIZE;
 
@@ -1015,9 +1024,11 @@ int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
 		engine->submit_request = i915_guc_submit;
 
 		/* Replay the current set of previously submitted requests */
-		list_for_each_entry(request, &engine->request_list, link)
+		list_for_each_entry(request, &engine->request_list, link) {
+			client->wq_rsvd += sizeof(struct guc_wq_item);
 			if (i915_sw_fence_done(&request->submit))
 				i915_guc_submit(request);
+		}
 	}
 
 	return 0;

drivers/gpu/drm/i915/intel_guc.h

@@ -78,9 +78,11 @@ struct i915_guc_client {
 	uint16_t doorbell_id;
 	uint16_t padding[3];		/* Maintain alignment		*/
 
+	spinlock_t wq_lock;
 	uint32_t wq_offset;
 	uint32_t wq_size;
 	uint32_t wq_tail;
+	uint32_t wq_rsvd;
 	uint32_t no_wq_space;
 	uint32_t b_fail;
 	int retcode;