[PATCH 2/2] drm/i915: Add WA for planes ending close to left screen edge

[Imre Deak <imre.deak@intel.com>]

While running the kms_plane clipping test I noticed a similar problem to
the one described in Display WA #1175. In this case, similarly for
planes other than the cursor, with 1 or 3 pixels visible from the left
edge of the screen to the end of the plane and an odd plane X offset
used for clipping causes the same kind of underflow and display
corruption as described for WA #1175. Fix this in a similar way as that
WA rejecting planes ending <4 pixels from the left screen edge.

Testcase: igt/kms_plane/plane-clipping-pipe-*-planes
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3d931b652795..ab04ef471921 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2945,12 +2945,16 @@ static int skl_check_main_surface(const struct intel_crtc_state *crtc_state,
 	 * Planes other than the cursor may cause FIFO underflow and display
 	 * corruption if starting less than 4 pixels from the right edge of
 	 * the screen.
+	 * Besides the above WA fix the similar problem, where planes other
+	 * than the cursor ending less than 4 pixels from the left edge of the
+	 * screen may cause FIFO underflow and display corruption.
 	 */
 	if ((IS_GEMINILAKE(dev_priv) || IS_CANNONLAKE(dev_priv)) &&
-	    dst_x > pipe_src_w - 4) {
-		DRM_DEBUG_KMS("requested plane X start position %d invalid (valid range %d-%d)\n",
-			      dst_x,
-			      0, pipe_src_w - 4);
+	    (dst_x + w < 4 || dst_x > pipe_src_w - 4)) {
+		DRM_DEBUG_KMS("requested plane X %s position %d invalid (valid range %d-%d)\n",
+			      dst_x + w < 4 ? "end" : "start",
+			      dst_x + w < 4 ? dst_x + w : dst_x,
+			      4, pipe_src_w - 4);
 		return -EINVAL;
 	}
 
-- 
2.13.2

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