[Intel-gfx] [PATCH] drm/i915/gen9: fix the WM memory bandwidth WA for Y tiling cases

[Paulo Zanoni]

The previous spec version said "double Ytile planes minimum lines",
and I interpreted this as referring to what the spec calls "Y tile
minimum", but in fact it was referring to what the spec calls "Minimum
Scanlines for Y tile". I noticed that Mahesh Kumar had a different
interpretation, so I sent and email to the spec authors and got
clarification on the correct meaning. Also, BSpec was updated and
should be clear now.

Fixes: ee3d532fcb64 ("drm/i915/gen9: unconditionally apply the memory bandwidth WA")
Cc: stable at vger.kernel.org
Cc: Mahesh Kumar <mahesh1.kumar at intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index cc9e0c0..653525f 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3624,6 +3624,9 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 		y_min_scanlines = 4;
 	}
 
+	if (apply_memory_bw_wa)
+		y_min_scanlines *= 2;
+
 	plane_bytes_per_line = width * cpp;
 	if (fb->modifier[0] == I915_FORMAT_MOD_Y_TILED ||
 	    fb->modifier[0] == I915_FORMAT_MOD_Yf_TILED) {
@@ -3644,8 +3647,6 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 				 plane_blocks_per_line);
 
 	y_tile_minimum = plane_blocks_per_line * y_min_scanlines;
-	if (apply_memory_bw_wa)
-		y_tile_minimum *= 2;
 
 	if (fb->modifier[0] == I915_FORMAT_MOD_Y_TILED ||
 	    fb->modifier[0] == I915_FORMAT_MOD_Yf_TILED) {
-- 
2.7.4