[PATCH 3/4] drm/i915: Insert a full mb() before reading the seqno from the status page

[Chris Wilson <chris@chris-wilson.co.uk>]

Hopefully this will reduce a few of the missed IRQ warnings.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c |    8 +++++++-
 drivers/gpu/drm/i915/intel_ringbuffer.h |    2 --
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index e069e69..133beb6 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -704,14 +704,18 @@ gen6_ring_get_seqno(struct intel_ring_buffer *ring, bool lazy_coherency)
 	/* Workaround to force correct ordering between irq and seqno writes on
 	 * ivb (and maybe also on snb) by reading from a CS register (like
 	 * ACTHD) before reading the status page. */
-	if (!lazy_coherency)
+	if (!lazy_coherency) {
 		intel_ring_get_active_head(ring);
+		mb();
+	}
 	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
 static u32
 ring_get_seqno(struct intel_ring_buffer *ring, bool lazy_coherency)
 {
+	if (!lazy_coherency)
+		mb();
 	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
@@ -719,6 +723,8 @@ static u32
 pc_render_get_seqno(struct intel_ring_buffer *ring, bool lazy_coherency)
 {
 	struct pipe_control *pc = ring->private;
+	if (!lazy_coherency)
+		mb();
 	return pc->cpu_page[0];
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 2ea7a31..40b252e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -160,8 +160,6 @@ static inline u32
 intel_read_status_page(struct intel_ring_buffer *ring,
 		       int reg)
 {
-	/* Ensure that the compiler doesn't optimize away the load. */
-	barrier();
 	return ring->status_page.page_addr[reg];
 }
 
-- 
1.7.10.4