[Intel-gfx] [PATCH] drm/i915: Enable hw workaround to bypass alpha

[Vandita Kulkarni]

Alpha blending with alpha 0 and 0xff passes through
alpha math and rounding logic causing differences
compared to fully transparent or opaque plane,resulting
in CRC mismatch.
This WA on icl and above enables hardware to bypass alpha
math and rounding for per pixel alpha values of 00 and 0xff

Signed-off-by: Vandita Kulkarni <vandita.kulkarni at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h      |  8 ++++++++
 drivers/gpu/drm/i915/intel_display.c | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 4bfd7a9..6e59bfe 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -7366,6 +7366,14 @@ enum {
 #define BDW_SCRATCH1					_MMIO(0xb11c)
 #define  GEN9_LBS_SLA_RETRY_TIMER_DECREMENT_ENABLE	(1 << 2)
 
+/*GEN11 chicken */
+#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)
+
 /* PCH */
 
 /* south display engine interrupt: IBX */
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2c8fef3..ca5882c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5632,6 +5632,7 @@ static void haswell_crtc_enable(struct intel_crtc_state *pipe_config,
 	struct intel_atomic_state *old_intel_state =
 		to_intel_atomic_state(old_state);
 	bool psl_clkgate_wa;
+	u32 pipe_chicken;
 
 	if (WARN_ON(intel_crtc->active))
 		return;
@@ -5691,6 +5692,17 @@ static void haswell_crtc_enable(struct intel_crtc_state *pipe_config,
 	 */
 	intel_color_load_luts(&pipe_config->base);
 
+	/*
+	 * Display WA #1153: enable hardware to bypass the alpha math
+	 * and rounding for per-pixel values 00 and 0xff
+	 */
+	if (INTEL_GEN(dev_priv) >= 11) {
+		pipe_chicken = I915_READ(PIPE_CHICKEN(pipe));
+		if (!(pipe_chicken & PER_PIXEL_ALPHA_BYPASS_EN))
+			I915_WRITE_FW(PIPE_CHICKEN(pipe),
+				  pipe_chicken | PER_PIXEL_ALPHA_BYPASS_EN);
+	}
+
 	intel_ddi_set_pipe_settings(pipe_config);
 	if (!transcoder_is_dsi(cpu_transcoder))
 		intel_ddi_enable_transcoder_func(pipe_config);
-- 
1.9.1