drm/i915/display: Handle lane polarity for DDI port

Lane Reversal is required for some of the DDI ports. This information
is populated in VBT and driver should read the same and set the
polarity while enabling the port. This patch handles the same.

It helps fix a display blankout issue on DP ports on certain
platforms.

Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210211114209.23866-1-uma.shankar@intel.com

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

@@ -2674,6 +2674,23 @@ intel_bios_is_lspcon_present(const struct drm_i915_private *i915,
 	return HAS_LSPCON(i915) && child && child->lspcon;
 }
 
+/**
+ * intel_bios_is_lane_reversal_needed - if lane reversal needed on port
+ * @i915:       i915 device instance
+ * @port:       port to check
+ *
+ * Return true if port requires lane reversal
+ */
+bool
+intel_bios_is_lane_reversal_needed(const struct drm_i915_private *i915,
+				   enum port port)
+{
+	const struct child_device_config *child =
+		i915->vbt.ddi_port_info[port].child;
+
+	return child && child->lane_reversal;
+}
+
 enum aux_ch intel_bios_port_aux_ch(struct drm_i915_private *dev_priv,
 				   enum port port)
 {

drivers/gpu/drm/i915/display/intel_bios.h

@@ -241,6 +241,8 @@ bool intel_bios_is_port_hpd_inverted(const struct drm_i915_private *i915,
 				     enum port port);
 bool intel_bios_is_lspcon_present(const struct drm_i915_private *i915,
 				  enum port port);
+bool intel_bios_is_lane_reversal_needed(const struct drm_i915_private *i915,
+					enum port port);
 enum aux_ch intel_bios_port_aux_ch(struct drm_i915_private *dev_priv, enum port port);
 bool intel_bios_get_dsc_params(struct intel_encoder *encoder,
 			       struct intel_crtc_state *crtc_state,

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

@@ -4082,6 +4082,9 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
 			intel_de_read(dev_priv, DDI_BUF_CTL(port))
 			& (DDI_BUF_PORT_REVERSAL | DDI_A_4_LANES);
 
+	if (intel_bios_is_lane_reversal_needed(dev_priv, port))
+		dig_port->saved_port_bits |= DDI_BUF_PORT_REVERSAL;
+
 	dig_port->dp.output_reg = INVALID_MMIO_REG;
 	dig_port->max_lanes = intel_ddi_max_lanes(dig_port);
 	dig_port->aux_ch = intel_bios_port_aux_ch(dev_priv, port);