[Intel-gfx] [PATCH v2 3/3] drm/i915: Prevent MI_DISPLAY_FLIP straddling two cachelines on IVB

[ville.syrjala at linux.intel.com]

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

According to BSpec the entire MI_DISPLAY_FLIP packet must be contained
in a single cacheline. Make sure that happens.

v2: Use intel_ring_begin_cacheline_safe()

Cc: Bjoern C <lkml at call-home.ch>
Cc: Alexandru DAMIAN <alexandru.damian at intel.com>
Cc: Enrico Tagliavini <enrico.tagliavini at gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=74053
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 0c25310..361a9a9 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8579,7 +8579,7 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 	struct intel_ring_buffer *ring;
 	uint32_t plane_bit = 0;
-	int len, ret;
+	int extra, len = 0, ret;
 
 	ring = obj->ring;
 	if (IS_VALLEYVIEW(dev) || ring == NULL || ring->id != RCS)
@@ -8605,11 +8605,14 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
 		goto err_unpin;
 	}
 
-	len = 4;
 	if (ring->id == RCS)
 		len += 6;
 
-	ret = intel_ring_begin(ring, len);
+	/*
+	 * BSpec MI_DISPLAY_FLIP for IVB:
+	 * "The full packet must be contained within the same cache line."
+	 */
+	ret = intel_ring_begin_cacheline_safe(ring, len, 4, len + 4, &extra);
 	if (ret)
 		goto err_unpin;
 
@@ -8634,6 +8637,9 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
 		intel_ring_emit(ring, ring->scratch.gtt_offset + 256);
 	}
 
+	while (extra--)
+		intel_ring_emit(ring, MI_NOOP);
+
 	intel_ring_emit(ring, MI_DISPLAY_FLIP_I915 | plane_bit);
 	intel_ring_emit(ring, (fb->pitches[0] | obj->tiling_mode));
 	intel_ring_emit(ring, i915_gem_obj_ggtt_offset(obj) + intel_crtc->dspaddr_offset);
-- 
1.8.3.2