[Intel-gfx] [PATCH] drm/i915: Implement display w/a #1143

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

Apparently SKL/KBL need some manual help to get the
programmed HDMI vswing to stick. Implement the relevant
workaround (display w/a #1143).

Note that the relevant chicken bits live in a transcoder register
even though the bits affect a specific DDI port rather than a
specific transcoder. Hence we must pick the correct transcoder
register instance based on the port rather than based on the
cpu_transcoder.

Also note that for completeness I included support for DDI A/E
in the code even though we never have HDMI on those ports.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h  |  8 ++++++--
 drivers/gpu/drm/i915/intel_ddi.c | 42 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 10e1269ad6af..2e6d0dc01dc7 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -7012,8 +7012,12 @@ enum {
 #define CHICKEN_TRANS_A         0x420c0
 #define CHICKEN_TRANS_B         0x420c4
 #define CHICKEN_TRANS(trans) _MMIO_TRANS(trans, CHICKEN_TRANS_A, CHICKEN_TRANS_B)
-#define PSR2_VSC_ENABLE_PROG_HEADER    (1<<12)
-#define PSR2_ADD_VERTICAL_LINE_COUNT   (1<<15)
+#define  DDI_TRAINING_OVERRIDE_ENABLE	(1<<19)
+#define  DDI_TRAINING_OVERRIDE_VALUE	(1<<18)
+#define  DDIE_TRAINING_OVERRIDE_ENABLE	(1<<17) /* CHICKEN_TRANS_A only */
+#define  DDIE_TRAINING_OVERRIDE_VALUE	(1<<16) /* CHICKEN_TRANS_A only */
+#define  PSR2_ADD_VERTICAL_LINE_COUNT   (1<<15)
+#define  PSR2_VSC_ENABLE_PROG_HEADER    (1<<12)
 
 #define DISP_ARB_CTL	_MMIO(0x45000)
 #define  DISP_FBC_MEMORY_WAKE		(1<<31)
diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 6260a882fbe4..7b1ab003279f 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -2433,6 +2433,48 @@ static void intel_enable_ddi_hdmi(struct intel_encoder *encoder,
 					  crtc_state->hdmi_high_tmds_clock_ratio,
 					  crtc_state->hdmi_scrambling);
 
+	/* Display WA #1143: skl,kbl */
+	if (IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv)) {
+		/*
+		 * For some reason these chicken bits have been
+		 * stuffed into a transcoder register, event though
+		 * the bits affect a specific DDI port rather than
+		 * a specific transcoder.
+		 */
+		static const enum transcoder port_to_transcoder[] = {
+			[PORT_A] = TRANSCODER_EDP,
+			[PORT_B] = TRANSCODER_A,
+			[PORT_C] = TRANSCODER_B,
+			[PORT_D] = TRANSCODER_C,
+			[PORT_E] = TRANSCODER_A,
+		};
+		enum transcoder transcoder = port_to_transcoder[port];
+		u32 val;
+
+		val = I915_READ(CHICKEN_TRANS(transcoder));
+
+		if (port == PORT_E)
+			val |= DDIE_TRAINING_OVERRIDE_ENABLE |
+				DDIE_TRAINING_OVERRIDE_VALUE;
+		else
+			val |= DDI_TRAINING_OVERRIDE_ENABLE |
+				DDI_TRAINING_OVERRIDE_VALUE;
+
+		I915_WRITE(CHICKEN_TRANS(transcoder), val);
+		POSTING_READ(CHICKEN_TRANS(transcoder));
+
+		udelay(1);
+
+		if (port == PORT_E)
+			val &= ~(DDIE_TRAINING_OVERRIDE_ENABLE |
+				 DDIE_TRAINING_OVERRIDE_VALUE);
+		else
+			val &= ~(DDI_TRAINING_OVERRIDE_ENABLE |
+				 DDI_TRAINING_OVERRIDE_VALUE);
+
+		I915_WRITE(CHICKEN_TRANS(transcoder), val);
+	}
+
 	/* In HDMI/DVI mode, the port width, and swing/emphasis values
 	 * are ignored so nothing special needs to be done besides
 	 * enabling the port.
-- 
2.13.6