[Intel-gfx] [PATCH 1/2] drm/i915: Don't allow ring tail to reach the same cacheline as head

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

According to BSpec the ring head and tail pointers must not be
on the same cacheline when head > tail. The easiest way to enforce
this is to reduce the reported ring space.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_dma.c         |    2 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c |    4 ++--
 drivers/gpu/drm/i915/intel_ringbuffer.h |    2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 2cba7b4..d184727 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -168,7 +168,7 @@ void i915_kernel_lost_context(struct drm_device * dev)
 
 	ring->head = I915_READ_HEAD(ring) & HEAD_ADDR;
 	ring->tail = I915_READ_TAIL(ring) & TAIL_ADDR;
-	ring->space = ring->head - (ring->tail + 8);
+	ring->space = ring->head - (ring->tail + 64);
 	if (ring->space < 0)
 		ring->space += ring->size;
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index c828169..70a184e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -46,7 +46,7 @@ struct pipe_control {
 
 static inline int ring_space(struct intel_ring_buffer *ring)
 {
-	int space = (ring->head & HEAD_ADDR) - (ring->tail + 8);
+	int space = (ring->head & HEAD_ADDR) - (ring->tail + 64);
 	if (space < 0)
 		space += ring->size;
 	return space;
@@ -1163,7 +1163,7 @@ static int intel_ring_wait_request(struct intel_ring_buffer *ring, int n)
 		if (request->tail == -1)
 			continue;
 
-		space = request->tail - (ring->tail + 8);
+		space = request->tail - (ring->tail + 64);
 		if (space < 0)
 			space += ring->size;
 		if (space >= n) {
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 2ea7a31..b15f896 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -187,7 +187,7 @@ void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring);
 int __must_check intel_wait_ring_buffer(struct intel_ring_buffer *ring, int n);
 static inline int intel_wait_ring_idle(struct intel_ring_buffer *ring)
 {
-	return intel_wait_ring_buffer(ring, ring->size - 8);
+	return intel_wait_ring_buffer(ring, ring->size - 64);
 }
 
 int __must_check intel_ring_begin(struct intel_ring_buffer *ring, int n);
-- 
1.7.8.6