drm/i915/dp: fix DG1 and RKL max source rates

Combo phy is limited to 5.4 GHz on low-voltage SKUs, but both eDP and DP
can do 8.1 GHz on combo phy.

Bspec: 49182, 49205, 49202

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210901160402.24816-5-animesh.manna@intel.com

drivers/gpu/drm/i915/display/intel_dp.c

@@ -325,6 +325,18 @@ static int ehl_max_source_rate(struct intel_dp *intel_dp)
 	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;
+}
+
 static void
 intel_dp_set_source_rates(struct intel_dp *intel_dp)
 {
@@ -360,6 +372,8 @@ intel_dp_set_source_rates(struct intel_dp *intel_dp)
 		size = ARRAY_SIZE(icl_rates);
 		if (IS_DG2(dev_priv))
 			max_rate = dg2_max_source_rate(intel_dp);
+		else if (IS_DG1(dev_priv) || IS_ROCKETLAKE(dev_priv))
+			max_rate = dg1_max_source_rate(intel_dp);
 		else if (IS_JSL_EHL(dev_priv))
 			max_rate = ehl_max_source_rate(intel_dp);
 		else