drm/radeon: align ring writes to 16 dwords boundaries.

On some radeon GPUs this appears to introduce another level of
stability around interacting with the ring.

Its pretty much what fglrx appears to do.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_cp.c

@@ -1950,3 +1950,35 @@ int radeon_driver_unload(struct drm_device *dev)
 	dev->dev_private = NULL;
 	return 0;
 }
+
+void radeon_commit_ring(drm_radeon_private_t *dev_priv)
+{
+	int i;
+	u32 *ring;
+	int tail_aligned;
+
+	/* check if the ring is padded out to 16-dword alignment */
+
+	tail_aligned = dev_priv->ring.tail & 0xf;
+	if (tail_aligned) {
+		int num_p2 = 16 - tail_aligned;
+
+		ring = dev_priv->ring.start;
+		/* pad with some CP_PACKET2 */
+		for (i = 0; i < num_p2; i++)
+			ring[dev_priv->ring.tail + i] = CP_PACKET2();
+
+		dev_priv->ring.tail += i;
+
+		dev_priv->ring.space -= num_p2 * sizeof(u32);
+	}
+
+	dev_priv->ring.tail &= dev_priv->ring.tail_mask;
+
+	DRM_MEMORYBARRIER();
+	GET_RING_HEAD( dev_priv );
+
+	RADEON_WRITE( RADEON_CP_RB_WPTR, dev_priv->ring.tail );
+	/* read from PCI bus to ensure correct posting */
+	RADEON_READ( RADEON_CP_RB_RPTR );
+}

drivers/gpu/drm/radeon/radeon_drv.h

@@ -1376,15 +1376,16 @@ do {								\
 
 #define RADEON_VERBOSE	0
 
-#define RING_LOCALS	int write, _nr; unsigned int mask; u32 *ring;
+#define RING_LOCALS	int write, _nr, _align_nr; unsigned int mask; u32 *ring;
 
 #define BEGIN_RING( n ) do {						\
 	if ( RADEON_VERBOSE ) {						\
 		DRM_INFO( "BEGIN_RING( %d )\n", (n));			\
 	}								\
-	if ( dev_priv->ring.space <= (n) * sizeof(u32) ) {		\
+	_align_nr = (n + 0xf) & ~0xf;					\
+	if (dev_priv->ring.space <= (_align_nr * sizeof(u32))) {	\
                 COMMIT_RING();						\
-		radeon_wait_ring( dev_priv, (n) * sizeof(u32) );	\
+		radeon_wait_ring( dev_priv, _align_nr * sizeof(u32));	\
 	}								\
 	_nr = n; dev_priv->ring.space -= (n) * sizeof(u32);		\
 	ring = dev_priv->ring.start;					\
@@ -1406,14 +1407,11 @@ do {								\
 		dev_priv->ring.tail = write;				\
 } while (0)
 
+extern void radeon_commit_ring(drm_radeon_private_t *dev_priv);
+
 #define COMMIT_RING() do {						\
-	/* Flush writes to ring */					\
-	DRM_MEMORYBARRIER();						\
-	GET_RING_HEAD( dev_priv );					\
-	RADEON_WRITE( RADEON_CP_RB_WPTR, dev_priv->ring.tail );		\
-	/* read from PCI bus to ensure correct posting */		\
-	RADEON_READ( RADEON_CP_RB_RPTR );				\
-} while (0)
+		radeon_commit_ring(dev_priv);				\
+	} while(0)
 
 #define OUT_RING( x ) do {						\
 	if ( RADEON_VERBOSE ) {						\