[Intel-gfx] [PATCH] drm/i915/display: Re-add check for low voltage sku for max dp source rate

[Jason A. Donenfeld]

This reverts commit 73867c8709b569cdd7fda67f01dfe02c8d055521, which, on
an i7-11850H iGPU with a Thinkpad X1 Extreme Gen 4, attached to a LG
LP160UQ1-SPB1 embedded panel, causes wild flickering glitching
technicolor pyrotechnics on resumption from suspend. The display shows
strobing colors in an utter disaster explosion of pantone, as though
bombs were dropped on the leprechauns at the base of the rainbow.

Rebooting the machine fixes the issue, presumably because the display is
initialized by firmware rather than by i915. Otherwise, the GPU appears
to work fine.

Bisection traced it back to this commit, which makes sense given the
issues.

Fixes: 73867c8709b5 ("drm/i915/display: Remove check for low voltage sku for max dp source rate")
Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
Cc: Imre Deak <imre.deak at intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Uma Shankar <uma.shankar at intel.com>
Cc: Animesh Manna <animesh.manna at intel.com>
Cc: Jani Saarinen <jani.saarinen at intel.com>
Signed-off-by: Jason A. Donenfeld <Jason at zx2c4.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 32 ++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index e4a79c11fd25..ff67899522cf 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -388,13 +388,23 @@ static int dg2_max_source_rate(struct intel_dp *intel_dp)
 	return intel_dp_is_edp(intel_dp) ? 810000 : 1350000;
 }
 
+static bool is_low_voltage_sku(struct drm_i915_private *i915, enum phy phy)
+{
+	u32 voltage;
+
+	voltage = intel_de_read(i915, ICL_PORT_COMP_DW3(phy)) & VOLTAGE_INFO_MASK;
+
+	return voltage == VOLTAGE_INFO_0_85V;
+}
+
 static int icl_max_source_rate(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
 	enum phy phy = intel_port_to_phy(dev_priv, dig_port->base.port);
 
-	if (intel_phy_is_combo(dev_priv, phy) && !intel_dp_is_edp(intel_dp))
+	if (intel_phy_is_combo(dev_priv, phy) &&
+	    (is_low_voltage_sku(dev_priv, phy) || !intel_dp_is_edp(intel_dp)))
 		return 540000;
 
 	return 810000;
@@ -402,7 +412,23 @@ static int icl_max_source_rate(struct intel_dp *intel_dp)
 
 static int ehl_max_source_rate(struct intel_dp *intel_dp)
 {
-	if (intel_dp_is_edp(intel_dp))
+	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
+	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
+	enum phy phy = intel_port_to_phy(dev_priv, dig_port->base.port);
+
+	if (intel_dp_is_edp(intel_dp) || is_low_voltage_sku(dev_priv, phy))
+		return 540000;
+
+	return 810000;
+}
+
+static int dg1_max_source_rate(struct intel_dp *intel_dp)
+{
+	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
+	struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
+	enum phy phy = intel_port_to_phy(i915, dig_port->base.port);
+
+	if (intel_phy_is_combo(i915, phy) && is_low_voltage_sku(i915, phy))
 		return 540000;
 
 	return 810000;
@@ -445,7 +471,7 @@ intel_dp_set_source_rates(struct intel_dp *intel_dp)
 			max_rate = dg2_max_source_rate(intel_dp);
 		else if (IS_ALDERLAKE_P(dev_priv) || IS_ALDERLAKE_S(dev_priv) ||
 			 IS_DG1(dev_priv) || IS_ROCKETLAKE(dev_priv))
-			max_rate = 810000;
+			max_rate = dg1_max_source_rate(intel_dp);
 		else if (IS_JSL_EHL(dev_priv))
 			max_rate = ehl_max_source_rate(intel_dp);
 		else
-- 
2.35.1