drm/i915/guc: Clean up locks in GuC

For now, remove the spinlocks that protected the GuC's
statistics block and work queue; they are only accessed
by code that already holds the global struct_mutex, and
so are redundant (until the big struct_mutex rewrite!).

The specific problem that the spinlocks caused was that
if the work queue was full, the driver would try to
spinwait for one jiffy, but with interrupts disabled the
jiffy count would not advance, leading to a system hang.
The issue was found using test case igt/gem_close_race.

The new version will usleep() instead, still holding
the struct_mutex but without any spinlocks.

v4: Reorganize commit message (Dave Gordon)
v3: Remove unnecessary whitespace churn
v2: Clean up wq_lock too
v1: Clean up host2guc lock as well

Signed-off-by: Alex Dai <yu.dai@intel.com>
Reviewed-by: Dave Gordon <david.s.gordon@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449104189-27591-1-git-send-email-yu.dai@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2469,15 +2469,15 @@ static int i915_guc_info(struct seq_file *m, void *data)
 	if (!HAS_GUC_SCHED(dev_priv->dev))
 		return 0;
 
+	if (mutex_lock_interruptible(&dev->struct_mutex))
+		return 0;
+
 	/* Take a local copy of the GuC data, so we can dump it at leisure */
-	spin_lock(&dev_priv->guc.host2guc_lock);
 	guc = dev_priv->guc;
-	if (guc.execbuf_client) {
-		spin_lock(&guc.execbuf_client->wq_lock);
+	if (guc.execbuf_client)
 		client = *guc.execbuf_client;
-		spin_unlock(&guc.execbuf_client->wq_lock);
-	}
-	spin_unlock(&dev_priv->guc.host2guc_lock);
+
+	mutex_unlock(&dev->struct_mutex);
 
 	seq_printf(m, "GuC total action count: %llu\n", guc.action_count);
 	seq_printf(m, "GuC action failure count: %u\n", guc.action_fail);

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -86,7 +86,6 @@ static int host2guc_action(struct intel_guc *guc, u32 *data, u32 len)
 		return -EINVAL;
 
 	intel_uncore_forcewake_get(dev_priv, FORCEWAKE_ALL);
-	spin_lock(&dev_priv->guc.host2guc_lock);
 
 	dev_priv->guc.action_count += 1;
 	dev_priv->guc.action_cmd = data[0];
@@ -119,7 +118,6 @@ static int host2guc_action(struct intel_guc *guc, u32 *data, u32 len)
 	}
 	dev_priv->guc.action_status = status;
 
-	spin_unlock(&dev_priv->guc.host2guc_lock);
 	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
 
 	return ret;
@@ -292,16 +290,12 @@ static uint32_t select_doorbell_cacheline(struct intel_guc *guc)
 	const uint32_t cacheline_size = cache_line_size();
 	uint32_t offset;
 
-	spin_lock(&guc->host2guc_lock);
-
 	/* Doorbell uses a single cache line within a page */
 	offset = offset_in_page(guc->db_cacheline);
 
 	/* Moving to next cache line to reduce contention */
 	guc->db_cacheline += cacheline_size;
 
-	spin_unlock(&guc->host2guc_lock);
-
 	DRM_DEBUG_DRIVER("selected doorbell cacheline 0x%x, next 0x%x, linesize %u\n",
 			offset, guc->db_cacheline, cacheline_size);
 
@@ -322,13 +316,11 @@ static uint16_t assign_doorbell(struct intel_guc *guc, uint32_t priority)
 	const uint16_t end = start + half;
 	uint16_t id;
 
-	spin_lock(&guc->host2guc_lock);
 	id = find_next_zero_bit(guc->doorbell_bitmap, end, start);
 	if (id == end)
 		id = GUC_INVALID_DOORBELL_ID;
 	else
 		bitmap_set(guc->doorbell_bitmap, id, 1);
-	spin_unlock(&guc->host2guc_lock);
 
 	DRM_DEBUG_DRIVER("assigned %s priority doorbell id 0x%x\n",
 			hi_pri ? "high" : "normal", id);
@@ -338,9 +330,7 @@ static uint16_t assign_doorbell(struct intel_guc *guc, uint32_t priority)
 
 static void release_doorbell(struct intel_guc *guc, uint16_t id)
 {
-	spin_lock(&guc->host2guc_lock);
 	bitmap_clear(guc->doorbell_bitmap, id, 1);
-	spin_unlock(&guc->host2guc_lock);
 }
 
 /*
@@ -487,16 +477,13 @@ static int guc_get_workqueue_space(struct i915_guc_client *gc, u32 *offset)
 	struct guc_process_desc *desc;
 	void *base;
 	u32 size = sizeof(struct guc_wq_item);
-	int ret = 0, timeout_counter = 200;
+	int ret = -ETIMEDOUT, timeout_counter = 200;
 
 	base = kmap_atomic(i915_gem_object_get_page(gc->client_obj, 0));
 	desc = base + gc->proc_desc_offset;
 
 	while (timeout_counter-- > 0) {
-		ret = wait_for_atomic(CIRC_SPACE(gc->wq_tail, desc->head,
-				gc->wq_size) >= size, 1);
-
-		if (!ret) {
+		if (CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size) >= size) {
 			*offset = gc->wq_tail;
 
 			/* advance the tail for next workqueue item */
@@ -505,7 +492,11 @@ static int guc_get_workqueue_space(struct i915_guc_client *gc, u32 *offset)
 
 			/* this will break the loop */
 			timeout_counter = 0;
+			ret = 0;
 		}
+
+		if (timeout_counter)
+			usleep_range(1000, 2000);
 	};
 
 	kunmap_atomic(base);
@@ -597,15 +588,12 @@ int i915_guc_submit(struct i915_guc_client *client,
 {
 	struct intel_guc *guc = client->guc;
 	enum intel_ring_id ring_id = rq->ring->id;
-	unsigned long flags;
 	int q_ret, b_ret;
 
 	/* Need this because of the deferred pin ctx and ring */
 	/* Shall we move this right after ring is pinned? */
 	lr_context_update(rq);
 
-	spin_lock_irqsave(&client->wq_lock, flags);
-
 	q_ret = guc_add_workqueue_item(client, rq);
 	if (q_ret == 0)
 		b_ret = guc_ring_doorbell(client);
@@ -620,12 +608,8 @@ int i915_guc_submit(struct i915_guc_client *client,
 	} else {
 		client->retcode = 0;
 	}
-	spin_unlock_irqrestore(&client->wq_lock, flags);
-
-	spin_lock(&guc->host2guc_lock);
 	guc->submissions[ring_id] += 1;
 	guc->last_seqno[ring_id] = rq->seqno;
-	spin_unlock(&guc->host2guc_lock);
 
 	return q_ret;
 }
@@ -768,7 +752,6 @@ static struct i915_guc_client *guc_client_alloc(struct drm_device *dev,
 	client->client_obj = obj;
 	client->wq_offset = GUC_DB_SIZE;
 	client->wq_size = GUC_WQ_SIZE;
-	spin_lock_init(&client->wq_lock);
 
 	client->doorbell_offset = select_doorbell_cacheline(guc);
 
@@ -871,8 +854,6 @@ int i915_guc_submission_init(struct drm_device *dev)
 	if (!guc->ctx_pool_obj)
 		return -ENOMEM;
 
-	spin_lock_init(&dev_priv->guc.host2guc_lock);
-
 	ida_init(&guc->ctx_ids);
 
 	guc_create_log(guc);

drivers/gpu/drm/i915/intel_guc.h

@@ -42,8 +42,6 @@ struct i915_guc_client {
 
 	uint32_t wq_offset;
 	uint32_t wq_size;
-
-	spinlock_t wq_lock;		/* Protects all data below	*/
 	uint32_t wq_tail;
 
 	/* GuC submission statistics & status */
@@ -95,8 +93,6 @@ struct intel_guc {
 
 	struct i915_guc_client *execbuf_client;
 
-	spinlock_t host2guc_lock;	/* Protects all data below	*/
-
 	DECLARE_BITMAP(doorbell_bitmap, GUC_MAX_DOORBELLS);
 	uint32_t db_cacheline;		/* Cyclic counter mod pagesize	*/