drm/radeon: fix ring free alignment calculations

fd.o bz#21849

We were aligning to +16 dwords, instead of to the next 16dword
boundary in the ring. Fix the calculation to go to the next 16dword
boundary when space checking.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_cp.c

@@ -2185,9 +2185,9 @@ void radeon_commit_ring(drm_radeon_private_t *dev_priv)
 
 	/* check if the ring is padded out to 16-dword alignment */
 
-	tail_aligned = dev_priv->ring.tail & 0xf;
+	tail_aligned = dev_priv->ring.tail & (RADEON_RING_ALIGN-1);
 	if (tail_aligned) {
-		int num_p2 = 16 - tail_aligned;
+		int num_p2 = RADEON_RING_ALIGN - tail_aligned;
 
 		ring = dev_priv->ring.start;
 		/* pad with some CP_PACKET2 */

drivers/gpu/drm/radeon/radeon_drv.h

@@ -1964,11 +1964,14 @@ do {								\
 
 #define RING_LOCALS	int write, _nr, _align_nr; unsigned int mask; u32 *ring;
 
+#define RADEON_RING_ALIGN 16
+
 #define BEGIN_RING( n ) do {						\
 	if ( RADEON_VERBOSE ) {						\
 		DRM_INFO( "BEGIN_RING( %d )\n", (n));			\
 	}								\
-	_align_nr = (n + 0xf) & ~0xf;					\
+	_align_nr = RADEON_RING_ALIGN - ((dev_priv->ring.tail + n) & (RADEON_RING_ALIGN-1));	\
+	_align_nr += n;							\
 	if (dev_priv->ring.space <= (_align_nr * sizeof(u32))) {	\
                 COMMIT_RING();						\
 		radeon_wait_ring( dev_priv, _align_nr * sizeof(u32));	\