drm/i915/ringbuffer: Make IRQ refcnting atomic

In order to enforce the correct memory barriers for irq get/put, we need
to perform the actual counting using atomic operations.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem.c

@@ -2000,17 +2000,19 @@ i915_do_wait_request(struct drm_device *dev, uint32_t seqno,
 		trace_i915_gem_request_wait_begin(dev, seqno);
 
 		ring->waiting_seqno = seqno;
-		ring->irq_get(ring);
-		if (interruptible)
-			ret = wait_event_interruptible(ring->irq_queue,
-				i915_seqno_passed(ring->get_seqno(ring), seqno)
-				|| atomic_read(&dev_priv->mm.wedged));
-		else
-			wait_event(ring->irq_queue,
-				i915_seqno_passed(ring->get_seqno(ring), seqno)
-				|| atomic_read(&dev_priv->mm.wedged));
+		ret = -ENODEV;
+		if (ring->irq_get(ring)) {
+			if (interruptible)
+				ret = wait_event_interruptible(ring->irq_queue,
+							       i915_seqno_passed(ring->get_seqno(ring), seqno)
+							       || atomic_read(&dev_priv->mm.wedged));
+			else
+				wait_event(ring->irq_queue,
+					   i915_seqno_passed(ring->get_seqno(ring), seqno)
+					   || atomic_read(&dev_priv->mm.wedged));
 
-		ring->irq_put(ring);
+			ring->irq_put(ring);
+		}
 		ring->waiting_seqno = 0;
 
 		trace_i915_gem_request_wait_end(dev, seqno);
@@ -3157,14 +3159,15 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 		 * generation is designed to be run atomically and so is
 		 * lockless.
 		 */
-		ring->irq_get(ring);
-		ret = wait_event_interruptible(ring->irq_queue,
-					       i915_seqno_passed(ring->get_seqno(ring), seqno)
-					       || atomic_read(&dev_priv->mm.wedged));
-		ring->irq_put(ring);
+		if (ring->irq_get(ring)) {
+			ret = wait_event_interruptible(ring->irq_queue,
+						       i915_seqno_passed(ring->get_seqno(ring), seqno)
+						       || atomic_read(&dev_priv->mm.wedged));
+			ring->irq_put(ring);
 
-		if (ret == 0 && atomic_read(&dev_priv->mm.wedged))
-			ret = -EIO;
+			if (ret == 0 && atomic_read(&dev_priv->mm.wedged))
+				ret = -EIO;
+		}
 	}
 
 	if (ret == 0)

drivers/gpu/drm/i915/i915_irq.c

@@ -1186,10 +1186,9 @@ void i915_trace_irq_get(struct drm_device *dev, u32 seqno)
 	drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 	struct intel_ring_buffer *ring = LP_RING(dev_priv);
 
-	if (dev_priv->trace_irq_seqno == 0)
-		ring->irq_get(ring);
-
-	dev_priv->trace_irq_seqno = seqno;
+	if (dev_priv->trace_irq_seqno == 0 &&
+	    ring->irq_get(ring))
+		dev_priv->trace_irq_seqno = seqno;
 }
 
 static int i915_wait_irq(struct drm_device * dev, int irq_nr)
@@ -1211,10 +1210,12 @@ static int i915_wait_irq(struct drm_device * dev, int irq_nr)
 	if (master_priv->sarea_priv)
 		master_priv->sarea_priv->perf_boxes |= I915_BOX_WAIT;
 
-	ring->irq_get(ring);
-	DRM_WAIT_ON(ret, ring->irq_queue, 3 * DRM_HZ,
-		    READ_BREADCRUMB(dev_priv) >= irq_nr);
-	ring->irq_put(ring);
+	ret = -ENODEV;
+	if (ring->irq_get(ring)) {
+		DRM_WAIT_ON(ret, ring->irq_queue, 3 * DRM_HZ,
+			    READ_BREADCRUMB(dev_priv) >= irq_nr);
+		ring->irq_put(ring);
+	}
 
 	if (ret == -EBUSY) {
 		DRM_ERROR("EBUSY -- rec: %d emitted: %d\n",

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -327,25 +327,28 @@ ring_get_seqno(struct intel_ring_buffer *ring)
 	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
-static void
+static bool
 render_ring_get_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 
-	if (dev->irq_enabled && ++ring->irq_refcount == 1) {
+	if (!dev->irq_enabled)
+		return false;
+
+	if (atomic_inc_return(&ring->irq_refcount) == 1) {
 		drm_i915_private_t *dev_priv = dev->dev_private;
 		unsigned long irqflags;
 
 		spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
-
 		if (HAS_PCH_SPLIT(dev))
 			ironlake_enable_graphics_irq(dev_priv,
 						     GT_USER_INTERRUPT);
 		else
 			i915_enable_irq(dev_priv, I915_USER_INTERRUPT);
-
 		spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
 	}
+
+	return true;
 }
 
 static void
@@ -353,8 +356,7 @@ render_ring_put_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 
-	BUG_ON(dev->irq_enabled && ring->irq_refcount == 0);
-	if (dev->irq_enabled && --ring->irq_refcount == 0) {
+	if (atomic_dec_and_test(&ring->irq_refcount)) {
 		drm_i915_private_t *dev_priv = dev->dev_private;
 		unsigned long irqflags;
 
@@ -417,12 +419,15 @@ ring_add_request(struct intel_ring_buffer *ring,
 	return 0;
 }
 
-static void
+static bool
 ring_get_irq(struct intel_ring_buffer *ring, u32 flag)
 {
 	struct drm_device *dev = ring->dev;
 
-	if (dev->irq_enabled && ++ring->irq_refcount == 1) {
+	if (!dev->irq_enabled)
+	       return false;
+
+	if (atomic_inc_return(&ring->irq_refcount) == 1) {
 		drm_i915_private_t *dev_priv = dev->dev_private;
 		unsigned long irqflags;
 
@@ -430,6 +435,8 @@ ring_get_irq(struct intel_ring_buffer *ring, u32 flag)
 		ironlake_enable_graphics_irq(dev_priv, flag);
 		spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
 	}
+
+	return true;
 }
 
 static void
@@ -437,7 +444,7 @@ ring_put_irq(struct intel_ring_buffer *ring, u32 flag)
 {
 	struct drm_device *dev = ring->dev;
 
-	if (dev->irq_enabled && --ring->irq_refcount == 0) {
+	if (atomic_dec_and_test(&ring->irq_refcount)) {
 		drm_i915_private_t *dev_priv = dev->dev_private;
 		unsigned long irqflags;
 
@@ -447,16 +454,15 @@ ring_put_irq(struct intel_ring_buffer *ring, u32 flag)
 	}
 }
 
-
-static void
+static bool
 bsd_ring_get_irq(struct intel_ring_buffer *ring)
 {
-    ring_get_irq(ring, GT_BSD_USER_INTERRUPT);
+	return ring_get_irq(ring, GT_BSD_USER_INTERRUPT);
 }
 static void
 bsd_ring_put_irq(struct intel_ring_buffer *ring)
 {
-    ring_put_irq(ring, GT_BSD_USER_INTERRUPT);
+	ring_put_irq(ring, GT_BSD_USER_INTERRUPT);
 }
 
 static int
@@ -846,16 +852,16 @@ gen6_ring_dispatch_execbuffer(struct intel_ring_buffer *ring,
        return 0;
 }
 
-static void
+static bool
 gen6_bsd_ring_get_irq(struct intel_ring_buffer *ring)
 {
-    ring_get_irq(ring, GT_GEN6_BSD_USER_INTERRUPT);
+	return ring_get_irq(ring, GT_GEN6_BSD_USER_INTERRUPT);
 }
 
 static void
 gen6_bsd_ring_put_irq(struct intel_ring_buffer *ring)
 {
-    ring_put_irq(ring, GT_GEN6_BSD_USER_INTERRUPT);
+	ring_put_irq(ring, GT_GEN6_BSD_USER_INTERRUPT);
 }
 
 /* ring buffer for Video Codec for Gen6+ */
@@ -876,16 +882,16 @@ static const struct intel_ring_buffer gen6_bsd_ring = {
 
 /* Blitter support (SandyBridge+) */
 
-static void
+static bool
 blt_ring_get_irq(struct intel_ring_buffer *ring)
 {
-    ring_get_irq(ring, GT_BLT_USER_INTERRUPT);
+	return ring_get_irq(ring, GT_BLT_USER_INTERRUPT);
 }
 
 static void
 blt_ring_put_irq(struct intel_ring_buffer *ring)
 {
-    ring_put_irq(ring, GT_BLT_USER_INTERRUPT);
+	ring_put_irq(ring, GT_BLT_USER_INTERRUPT);
 }
 
 

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -54,8 +54,8 @@ struct  intel_ring_buffer {
 	u32		irq_seqno;		/* last seq seem at irq time */
 	u32		waiting_seqno;
 	u32		sync_seqno[I915_NUM_RINGS-1];
-	u32		irq_refcount;
-	void		(*irq_get)(struct intel_ring_buffer *ring);
+	atomic_t	irq_refcount;
+	bool __must_check (*irq_get)(struct intel_ring_buffer *ring);
 	void		(*irq_put)(struct intel_ring_buffer *ring);
 
 	int		(*init)(struct intel_ring_buffer *ring);