drm/i915: Add intel_ring_cachline_align()

intel_ring_cachline_align() emits MI_NOOPs until the ring tail is
aligned to a cacheline boundary.

Cc: Bjoern C <lkml@call-home.ch>
Cc: Alexandru DAMIAN <alexandru.damian@intel.com>
Cc: Enrico Tagliavini <enrico.tagliavini@gmail.com>
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org (prereq for the next patch)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

2 files changed, 22 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index b7f1742caf87..31b36c5ac894 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1653,6 +1653,27 @@ int intel_ring_begin(struct intel_ring_buffer *ring,
         return 0;
 }
 
+/* Align the ring tail to a cacheline boundary */
+int intel_ring_cacheline_align(struct intel_ring_buffer *ring)
+{
+        int num_dwords = (64 - (ring->tail & 63)) / sizeof(uint32_t);
+        int ret;
+
+        if (num_dwords == 0)
+                return 0;
+
+        ret = intel_ring_begin(ring, num_dwords);
+        if (ret)
+                return ret;
+
+        while (num_dwords--)
+                intel_ring_emit(ring, MI_NOOP);
+
+        intel_ring_advance(ring);
+
+        return 0;
+}
+
 void intel_ring_init_seqno(struct intel_ring_buffer *ring, u32 seqno)
 {
         struct drm_i915_private *dev_priv = ring->dev->dev_private;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 71a73f4fe252..0b243ce33714 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -233,6 +233,7 @@ intel_write_status_page(struct intel_ring_buffer *ring,
 void intel_cleanup_ring_buffer(struct intel_ring_buffer *ring);
 
 int __must_check intel_ring_begin(struct intel_ring_buffer *ring, int n);
+int __must_check intel_ring_cacheline_align(struct intel_ring_buffer *ring);
 static inline void intel_ring_emit(struct intel_ring_buffer *ring,
                                    u32 data)
 {