drm/i915/icl: Fix CRC mismatch error for DP link layer compliance

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)

v2: This is also needed to fix failing IGT test case kms_cursor_crc on
ICL.(Mika Kahola)
Make macros consistent with i915_reg.h comments.(Jani Nikula)

Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Aditya Swarup <aditya.swarup@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190307021412.18626-1-aditya.swarup@intel.com
References: https://bugs.freedesktop.org/show_bug.cgi?id=103232

drivers/gpu/drm/i915/i915_reg.h

@@ -7662,9 +7662,10 @@ enum {
 #define _PIPEA_CHICKEN				0x70038
 #define _PIPEB_CHICKEN				0x71038
 #define _PIPEC_CHICKEN				0x72038
-#define  PER_PIXEL_ALPHA_BYPASS_EN	(1 << 7)
 #define PIPE_CHICKEN(pipe)			_MMIO_PIPE(pipe, _PIPEA_CHICKEN,\
 							   _PIPEB_CHICKEN)
+#define   PIXEL_ROUNDING_TRUNC_FB_PASSTHRU 	(1 << 15)
+#define   PER_PIXEL_ALPHA_BYPASS_EN		(1 << 7)
 
 /* PCH */
 

drivers/gpu/drm/i915/intel_display.c

@@ -3933,7 +3933,13 @@ 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);
 }