drm/i915: Only populate aux_ch if really needed

Mixing VBT based AUX CH with platform defaults seems like
a recipe for conflicts. Let's only populate AUX CH if we
absolutely need it, that is only if we are dealing with
a DP output or a TC port (which need it due to some power
well shenanigans).

TODO: double check that real VBTs do in fact populate
      the AUX CH for HDMI TC legacy ports...

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230630155846.29931-3-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/g4x_hdmi.c

@@ -775,6 +775,5 @@ void g4x_hdmi_init(struct drm_i915_private *dev_priv,
 
 	intel_infoframe_init(dig_port);
 
-	dig_port->aux_ch = intel_dp_aux_ch(intel_encoder);
 	intel_hdmi_init_connector(dig_port, intel_connector);
 }

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

@@ -4676,6 +4676,14 @@ static bool port_strap_detected(struct drm_i915_private *i915, enum port port)
 	}
 }
 
+static bool need_aux_ch(struct intel_encoder *encoder, bool init_dp)
+{
+	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+	enum phy phy = intel_port_to_phy(i915, encoder->port);
+
+	return init_dp || intel_phy_is_tc(i915, phy);
+}
+
 void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
 {
 	struct intel_digital_port *dig_port;
@@ -4929,7 +4937,9 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
 
 	dig_port->dp.output_reg = INVALID_MMIO_REG;
 	dig_port->max_lanes = intel_ddi_max_lanes(dig_port);
-	dig_port->aux_ch = intel_dp_aux_ch(encoder);
+
+	if (need_aux_ch(encoder, init_dp))
+		dig_port->aux_ch = intel_dp_aux_ch(encoder);
 
 	if (intel_phy_is_tc(dev_priv, phy)) {
 		bool is_legacy =