[Intel-gfx] [PATCH v3 2/2] 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()
v3: Use intel_ring_cacheline_align() (Chris)

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 | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 0c25310..37527d4 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8609,6 +8609,20 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
 	if (ring->id == RCS)
 		len += 6;
 
+	/*
+	 * BSpec MI_DISPLAY_FLIP for IVB:
+	 * "The full packet must be contained within the same cache line."
+	 *
+	 * Currently the LRI+SRM+MI_DISPLAY_FLIP all fit within the same
+	 * cacheline, if we ever start emitting more commands before
+	 * the MI_DISPLAY_FLIP we may need to first emit everything else,
+	 * then do the cacheline alignment, and finally emit the
+	 * MI_DISPLAY_FLIP.
+	 */
+	ret = intel_ring_cacheline_align(ring);
+	if (ret)
+		goto err_unpin;
+
 	ret = intel_ring_begin(ring, len);
 	if (ret)
 		goto err_unpin;
-- 
1.8.3.2