[Intel-gfx] [PATCH] drm/i915/icl: Fix CRC mismatch error for DP link layer compliance

[Aditya Swarup]

Setting the pixel rounding bit to 1 in PIPE_CHICKEN register allows
to passthrough FB pixels unmodified across pipe. This fixes the failures
for DP link layer compliance tests 4.4.1.1, 4.4.1.2 & 4.4.1.3.
(Lineage #1605353570)

Cc: Clint Taylor <clinton.a.taylor at intel.com>
Cc: Mika Kahola <mika.kahola at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Signed-off-by: Aditya Swarup <aditya.swarup at intel.com>
---
WA for ICL DP compliance. It fixes failing test in igt for crc mismatch
wrt cursor plane. Can be searched using Lineage #1605353570.

 drivers/gpu/drm/i915/i915_reg.h      | 1 +
 drivers/gpu/drm/i915/intel_display.c | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index c9b868347481..4713fbb3e021 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -7663,6 +7663,7 @@ enum {
 #define _PIPEB_CHICKEN			0x71038
 #define _PIPEC_CHICKEN			0x72038
 #define  PER_PIXEL_ALPHA_BYPASS_EN	(1 << 7)
+#define PIXEL_ROUNDING_TRUNC_FB_PASSTHRU (1 << 15)
 #define PIPE_CHICKEN(pipe)		_MMIO_PIPE(pipe, _PIPEA_CHICKEN,\
 						   _PIPEB_CHICKEN)
 
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d852cb282060..92be3476fef1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3970,7 +3970,13 @@ static void icl_set_pipe_chicken(struct intel_crtc *crtc)
 	 * and rounding for per-pixel values 00 and 0xff
 	 */
 	tmp |= PER_PIXEL_ALPHA_BYPASS_EN;
-
+	/*
+	 * Display WA # 1605353570: icl
+	 * Set the pixel rounding bit to 1 for allowing
+	 * passthrough of Frame buffer pixels unmodified
+	 * across pipe
+	 */
+	tmp |= PIXEL_ROUNDING_TRUNC_FB_PASSTHRU;
 	I915_WRITE(PIPE_CHICKEN(pipe), tmp);
 }
 
-- 
2.17.1