drm/i915/rkl: Handle comp master/slave relationships for PHYs

Certain combo PHYs act as a compensation master to other PHYs and need
to be initialized with a special irefgen bit in the PORT_COMP_DW8
register.  Previously PHY A was the only compensation master (for PHYs
B & C), but RKL adds a fourth PHY which is slaved to PHY C instead.

Bspec: 49291
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Aditya Swarup <aditya.swarup@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200603211529.3005059-12-matthew.d.roper@intel.com

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

@@ -234,6 +234,27 @@ static bool ehl_vbt_ddi_d_present(struct drm_i915_private *i915)
 	return false;
 }
 
+static bool phy_is_master(struct drm_i915_private *dev_priv, enum phy phy)
+{
+	/*
+	 * Certain PHYs are connected to compensation resistors and act
+	 * as masters to other PHYs.
+	 *
+	 * ICL,TGL:
+	 *   A(master) -> B(slave), C(slave)
+	 * RKL:
+	 *   A(master) -> B(slave)
+	 *   C(master) -> D(slave)
+	 *
+	 * We must set the IREFGEN bit for any PHY acting as a master
+	 * to another PHY.
+	 */
+	if (IS_ROCKETLAKE(dev_priv) && phy == PHY_C)
+		return true;
+
+	return phy == PHY_A;
+}
+
 static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
 				       enum phy phy)
 {
@@ -245,7 +266,7 @@ static bool icl_combo_phy_verify_state(struct drm_i915_private *dev_priv,
 
 	ret = cnl_verify_procmon_ref_values(dev_priv, phy);
 
-	if (phy == PHY_A) {
+	if (phy_is_master(dev_priv, phy)) {
 		ret &= check_phy_reg(dev_priv, phy, ICL_PORT_COMP_DW8(phy),
 				     IREFGEN, IREFGEN);
 
@@ -356,7 +377,7 @@ static void icl_combo_phys_init(struct drm_i915_private *dev_priv)
 skip_phy_misc:
 		cnl_set_procmon_ref_values(dev_priv, phy);
 
-		if (phy == PHY_A) {
+		if (phy_is_master(dev_priv, phy)) {
 			val = intel_de_read(dev_priv, ICL_PORT_COMP_DW8(phy));
 			val |= IREFGEN;
 			intel_de_write(dev_priv, ICL_PORT_COMP_DW8(phy), val);