drm/i915: Respect alternate_aux_channel for all DDI ports

The VBT provides the platform a way to mix and match the DDI ports vs.
AUX channels. Currently we only trust the VBT for DDI E, which has no
corresponding AUX channel of its own. However it is possible that some
board might use some non-standard DDI vs. AUX port routing even for
the other ports. Perhaps for signal routing reasons or something,
So let's generalize this and trust the VBT for all ports.

For now we'll limit this to DDI platforms, as we trust the VBT a bit
more there anyway when it comes to the DDI ports. I've structured
the code in a way that would allow us to easily expand this to
other platforms as well, by simply filling in the ddi_port_info.

v2: Drop whitespace changes, keep MISSING_CASE() for unknown
    aux ch assignment, include a commit message, include debug
    message during init

Cc: stable@vger.kernel.org
Cc: Maarten Maathuis <madman2003@gmail.com>
Tested-by: Maarten Maathuis <madman2003@gmail.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=97877
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1476208368-5710-2-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jim Bride <jim.bride@linux.intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1109,6 +1109,44 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 	return ret;
 }
 
+static enum port intel_aux_port(struct drm_i915_private *dev_priv,
+				enum port port)
+{
+	const struct ddi_vbt_port_info *info =
+		&dev_priv->vbt.ddi_port_info[port];
+	enum port aux_port;
+
+	if (!info->alternate_aux_channel) {
+		DRM_DEBUG_KMS("using AUX %c for port %c (platform default)\n",
+			      port_name(port), port_name(port));
+		return port;
+	}
+
+	switch (info->alternate_aux_channel) {
+	case DP_AUX_A:
+		aux_port = PORT_A;
+		break;
+	case DP_AUX_B:
+		aux_port = PORT_B;
+		break;
+	case DP_AUX_C:
+		aux_port = PORT_C;
+		break;
+	case DP_AUX_D:
+		aux_port = PORT_D;
+		break;
+	default:
+		MISSING_CASE(info->alternate_aux_channel);
+		aux_port = PORT_A;
+		break;
+	}
+
+	DRM_DEBUG_KMS("using AUX %c for port %c (VBT)\n",
+		      port_name(aux_port), port_name(port));
+
+	return aux_port;
+}
+
 static i915_reg_t g4x_aux_ctl_reg(struct drm_i915_private *dev_priv,
 				       enum port port)
 {
@@ -1169,36 +1207,9 @@ static i915_reg_t ilk_aux_data_reg(struct drm_i915_private *dev_priv,
 	}
 }
 
-/*
- * On SKL we don't have Aux for port E so we rely
- * on VBT to set a proper alternate aux channel.
- */
-static enum port skl_porte_aux_port(struct drm_i915_private *dev_priv)
-{
-	const struct ddi_vbt_port_info *info =
-		&dev_priv->vbt.ddi_port_info[PORT_E];
-
-	switch (info->alternate_aux_channel) {
-	case DP_AUX_A:
-		return PORT_A;
-	case DP_AUX_B:
-		return PORT_B;
-	case DP_AUX_C:
-		return PORT_C;
-	case DP_AUX_D:
-		return PORT_D;
-	default:
-		MISSING_CASE(info->alternate_aux_channel);
-		return PORT_A;
-	}
-}
-
 static i915_reg_t skl_aux_ctl_reg(struct drm_i915_private *dev_priv,
 				       enum port port)
 {
-	if (port == PORT_E)
-		port = skl_porte_aux_port(dev_priv);
-
 	switch (port) {
 	case PORT_A:
 	case PORT_B:
@@ -1214,9 +1225,6 @@ static i915_reg_t skl_aux_ctl_reg(struct drm_i915_private *dev_priv,
 static i915_reg_t skl_aux_data_reg(struct drm_i915_private *dev_priv,
 					enum port port, int index)
 {
-	if (port == PORT_E)
-		port = skl_porte_aux_port(dev_priv);
-
 	switch (port) {
 	case PORT_A:
 	case PORT_B:
@@ -1254,7 +1262,8 @@ static i915_reg_t intel_aux_data_reg(struct drm_i915_private *dev_priv,
 static void intel_aux_reg_init(struct intel_dp *intel_dp)
 {
 	struct drm_i915_private *dev_priv = to_i915(intel_dp_to_dev(intel_dp));
-	enum port port = dp_to_dig_port(intel_dp)->port;
+	enum port port = intel_aux_port(dev_priv,
+					dp_to_dig_port(intel_dp)->port);
 	int i;
 
 	intel_dp->aux_ch_ctl_reg = intel_aux_ctl_reg(dev_priv, port);