drm/i915: Use a global lock for modifying global irq flags

We were attempting to use a per-ring spinlock whilst modifying global
IRQ flags. A recipe for rare missed interrupts.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -610,17 +610,18 @@ gen5_ring_get_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
 	if (!dev->irq_enabled)
 		return false;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (ring->irq_refcount++ == 0) {
 		dev_priv->gt_irq_mask &= ~ring->irq_enable_mask;
 		I915_WRITE(GTIMR, dev_priv->gt_irq_mask);
 		POSTING_READ(GTIMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 
 	return true;
 }
@@ -630,14 +631,15 @@ gen5_ring_put_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (--ring->irq_refcount == 0) {
 		dev_priv->gt_irq_mask |= ring->irq_enable_mask;
 		I915_WRITE(GTIMR, dev_priv->gt_irq_mask);
 		POSTING_READ(GTIMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 }
 
 static bool
@@ -645,17 +647,18 @@ i9xx_ring_get_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
 	if (!dev->irq_enabled)
 		return false;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (ring->irq_refcount++ == 0) {
 		dev_priv->irq_mask &= ~ring->irq_enable_mask;
 		I915_WRITE(IMR, dev_priv->irq_mask);
 		POSTING_READ(IMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 
 	return true;
 }
@@ -665,14 +668,15 @@ i9xx_ring_put_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (--ring->irq_refcount == 0) {
 		dev_priv->irq_mask |= ring->irq_enable_mask;
 		I915_WRITE(IMR, dev_priv->irq_mask);
 		POSTING_READ(IMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 }
 
 static bool
@@ -680,17 +684,18 @@ i8xx_ring_get_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
 	if (!dev->irq_enabled)
 		return false;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (ring->irq_refcount++ == 0) {
 		dev_priv->irq_mask &= ~ring->irq_enable_mask;
 		I915_WRITE16(IMR, dev_priv->irq_mask);
 		POSTING_READ16(IMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 
 	return true;
 }
@@ -700,14 +705,15 @@ i8xx_ring_put_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (--ring->irq_refcount == 0) {
 		dev_priv->irq_mask |= ring->irq_enable_mask;
 		I915_WRITE16(IMR, dev_priv->irq_mask);
 		POSTING_READ16(IMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 }
 
 void intel_ring_setup_status_page(struct intel_ring_buffer *ring)
@@ -786,6 +792,7 @@ gen6_ring_get_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
 	if (!dev->irq_enabled)
 	       return false;
@@ -795,14 +802,14 @@ gen6_ring_get_irq(struct intel_ring_buffer *ring)
 	 * blt/bsd rings on ivb. */
 	gen6_gt_force_wake_get(dev_priv);
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (ring->irq_refcount++ == 0) {
 		I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
 		dev_priv->gt_irq_mask &= ~ring->irq_enable_mask;
 		I915_WRITE(GTIMR, dev_priv->gt_irq_mask);
 		POSTING_READ(GTIMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 
 	return true;
 }
@@ -812,15 +819,16 @@ gen6_ring_put_irq(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	unsigned long flags;
 
-	spin_lock(&ring->irq_lock);
+	spin_lock_irqsave(&dev_priv->irq_lock, flags);
 	if (--ring->irq_refcount == 0) {
 		I915_WRITE_IMR(ring, ~0);
 		dev_priv->gt_irq_mask |= ring->irq_enable_mask;
 		I915_WRITE(GTIMR, dev_priv->gt_irq_mask);
 		POSTING_READ(GTIMR);
 	}
-	spin_unlock(&ring->irq_lock);
+	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
 
 	gen6_gt_force_wake_put(dev_priv);
 }
@@ -954,7 +962,6 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	ring->size = 32 * PAGE_SIZE;
 
 	init_waitqueue_head(&ring->irq_queue);
-	spin_lock_init(&ring->irq_lock);
 
 	if (I915_NEED_GFX_HWS(dev)) {
 		ret = init_status_page(ring);

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -56,8 +56,7 @@ struct  intel_ring_buffer {
 	 */
 	u32		last_retired_head;
 
-	spinlock_t	irq_lock;
-	u32		irq_refcount;
+	u32		irq_refcount;		/* protected by dev_priv->irq_lock */
 	u32		irq_enable_mask;	/* bitmask to enable ring interrupt */
 	u32		irq_seqno;		/* last seq seem at irq time */
 	u32		trace_irq_seqno;