[Intel-gfx] [PATCH] drm/i915/adlp: Add workaround to disable CMTG clock gating

[Imre Deak]

The driver doesn't depend atm on the common mode timing generator
functionality (it would be used for some power saving feature and panel
timing synchronization), however DMC will corrupt the CMTG registers
across DC5 entry/exit sequences unless the CMTG clock gating is
disabled. This in turn can lead to at least the DPLL0/1 configuration
getting stuck at their last state, which means we can't reprogram them
to a new config.

Add the corresponding Bspec workaround to prevent the above.

Cc: Uma Shankar <uma.shankar at intel.com>
Cc: José Roberto de Souza <jose.souza at intel.com>
Cc: Anshuman Gupta <anshuman.gupta at intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 18 ++++++++++++++++++
 drivers/gpu/drm/i915/i915_reg.h              |  3 +++
 2 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index bb0aebcc3ecd3..474d723a37454 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -13198,6 +13198,24 @@ static void intel_early_display_was(struct drm_i915_private *dev_priv)
 			     KBL_ARB_FILL_SPARE_13 | KBL_ARB_FILL_SPARE_14,
 			     KBL_ARB_FILL_SPARE_14);
 	}
+
+	if (IS_ADLP_DISPLAY_STEP(dev_priv, STEP_A0, STEP_B0)) {
+		uint32_t val;
+
+		/*
+		 * Wa_16011069516:adl-p[a0]
+		 *
+		 * All CMTG regs are unreliable until CMTG clock gating is
+		 * disabled, so we can only assume the default CMTG_CHICKEN
+		 * reg value and sanity check this assumption with a double
+		 * read, which presumably returns the correct value even with
+		 * clock gating on.
+		 */
+		val = intel_de_read(dev_priv, TRANS_CMTG_CHICKEN);
+		val = intel_de_read(dev_priv, TRANS_CMTG_CHICKEN);
+		intel_de_write(dev_priv, TRANS_CMTG_CHICKEN, DISABLE_DPT_CLK_GATING);
+		drm_WARN_ON(&dev_priv->drm, val &~ DISABLE_DPT_CLK_GATING);
+	}
 }
 
 static void ibx_sanitize_pch_hdmi_port(struct drm_i915_private *dev_priv,
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index c41f9083e2338..e02bd75dd1064 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -10208,6 +10208,9 @@ enum skl_power_gate {
 #define  PORT_SYNC_MODE_MASTER_SELECT_MASK	REG_GENMASK(2, 0)
 #define  PORT_SYNC_MODE_MASTER_SELECT(x)	REG_FIELD_PREP(PORT_SYNC_MODE_MASTER_SELECT_MASK, (x))
 
+#define TRANS_CMTG_CHICKEN		_MMIO(0x6fa90)
+#define  DISABLE_DPT_CLK_GATING		REG_BIT(1)
+
 /* DisplayPort Transport Control */
 #define _DP_TP_CTL_A			0x64040
 #define _DP_TP_CTL_B			0x64140
-- 
2.27.0