drm/i915: Remove intel_ring.last_retired_head

Storing the position of the breadcrumb of the last retired request as
a separate last_retired_head is superfluous as we always copy that into
head prior to recalculation of the intel_ring.space.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170321102552.24357-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1938,9 +1938,8 @@ static int i915_gem_framebuffer_info(struct seq_file *m, void *data)
 
 static void describe_ctx_ring(struct seq_file *m, struct intel_ring *ring)
 {
-	seq_printf(m, " (ringbuffer, space: %d, head: %u, tail: %u, last head: %d)",
-		   ring->space, ring->head, ring->tail,
-		   ring->last_retired_head);
+	seq_printf(m, " (ringbuffer, space: %d, head: %u, tail: %u)",
+		   ring->space, ring->head, ring->tail);
 }
 
 static int i915_context_status(struct seq_file *m, void *unused)

drivers/gpu/drm/i915/i915_gem_request.c

@@ -295,7 +295,7 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 	 * completion order.
 	 */
 	list_del(&request->ring_link);
-	request->ring->last_retired_head = request->postfix;
+	request->ring->head = request->postfix;
 	if (!--request->i915->gt.active_requests) {
 		GEM_BUG_ON(!request->i915->gt.awake);
 		mod_delayed_work(request->i915->wq,

drivers/gpu/drm/i915/intel_lrc.c

@@ -1260,7 +1260,6 @@ static void reset_common_ring(struct intel_engine_cs *engine,
 	ce->lrc_reg_state[CTX_RING_HEAD+1] = request->postfix;
 
 	request->ring->head = request->postfix;
-	request->ring->last_retired_head = -1;
 	intel_ring_update_space(request->ring);
 
 	/* Catch up with any missed context-switch interrupts */
@@ -2047,7 +2046,6 @@ void intel_lr_context_resume(struct drm_i915_private *dev_priv)
 			i915_gem_object_unpin_map(ce->state->obj);
 
 			ce->ring->head = ce->ring->tail = 0;
-			ce->ring->last_retired_head = -1;
 			intel_ring_update_space(ce->ring);
 		}
 	}

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -49,13 +49,7 @@ static int __intel_ring_space(int head, int tail, int size)
 
 void intel_ring_update_space(struct intel_ring *ring)
 {
-	if (ring->last_retired_head != -1) {
-		ring->head = ring->last_retired_head;
-		ring->last_retired_head = -1;
-	}
-
-	ring->space = __intel_ring_space(ring->head & HEAD_ADDR,
-					 ring->tail, ring->size);
+	ring->space = __intel_ring_space(ring->head, ring->tail, ring->size);
 }
 
 static int
@@ -618,12 +612,8 @@ static void reset_ring_common(struct intel_engine_cs *engine,
 		}
 
 		/* If the rq hung, jump to its breadcrumb and skip the batch */
-		if (request->fence.error == -EIO) {
-			struct intel_ring *ring = request->ring;
-
-			ring->head = request->postfix;
-			ring->last_retired_head = -1;
-		}
+		if (request->fence.error == -EIO)
+			request->ring->head = request->postfix;
 	} else {
 		engine->legacy_active_context = NULL;
 	}
@@ -1392,7 +1382,6 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
 	if (IS_I830(engine->i915) || IS_I845G(engine->i915))
 		ring->effective_size -= 2 * CACHELINE_BYTES;
 
-	ring->last_retired_head = -1;
 	intel_ring_update_space(ring);
 
 	vma = intel_ring_create_vma(engine->i915, size);
@@ -1571,10 +1560,8 @@ void intel_legacy_submission_resume(struct drm_i915_private *dev_priv)
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 
-	for_each_engine(engine, dev_priv, id) {
+	for_each_engine(engine, dev_priv, id)
 		engine->buffer->head = engine->buffer->tail;
-		engine->buffer->last_retired_head = -1;
-	}
 }
 
 static int ring_request_alloc(struct drm_i915_gem_request *request)

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -149,16 +149,6 @@ struct intel_ring {
 	int space;
 	int size;
 	int effective_size;
-
-	/** We track the position of the requests in the ring buffer, and
-	 * when each is retired we increment last_retired_head as the GPU
-	 * must have finished processing the request and so we know we
-	 * can advance the ringbuffer up to that position.
-	 *
-	 * last_retired_head is set to -1 after the value is consumed so
-	 * we can detect new retirements.
-	 */
-	u32 last_retired_head;
 };
 
 struct i915_gem_context;

drivers/gpu/drm/i915/selftests/mock_engine.c

@@ -118,7 +118,6 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
 	ring->vaddr = (void *)(ring + 1);
 
 	INIT_LIST_HEAD(&ring->request_list);
-	ring->last_retired_head = -1;
 	intel_ring_update_space(ring);
 
 	return ring;