drm/i915: check the DDC and AUX bits of the VBT on DDI machines

Our code currently assumes that port X will use the DP AUX channel X
and the DDC pin X. The VBT should tell us how things are mapped, so
add some WARNs in case we discover our assumptions are wrong (or in
case the VBT is just wrong, which is also perfectly possible).

Why would someone wire port B to AUX C and DDC D?

v2: Rebase
v3: Convert WARNs to DRM_DEBUG_KMS

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_bios.c

@@ -590,6 +590,8 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
 	struct ddi_vbt_port_info *info = &dev_priv->vbt.ddi_port_info[port];
 	uint8_t hdmi_level_shift;
 	int i, j;
+	bool is_dvi, is_dp;
+	uint8_t aux_channel;
 	/* Each DDI port can have more than one value on the "DVO Port" field,
 	 * so look for all the possible values for each port and abort if more
 	 * than one is found. */
@@ -622,6 +624,31 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
 	if (!child)
 		return;
 
+	aux_channel = child->raw[25];
+
+	is_dvi = child->common.device_type & (1 << 4);
+	is_dp = child->common.device_type & (1 << 2);
+
+	if (is_dvi) {
+		if (child->common.ddc_pin == 0x05 && port != PORT_B)
+			DRM_DEBUG_KMS("Unexpected DDC pin for port B\n");
+		if (child->common.ddc_pin == 0x04 && port != PORT_C)
+			DRM_DEBUG_KMS("Unexpected DDC pin for port C\n");
+		if (child->common.ddc_pin == 0x06 && port != PORT_D)
+			DRM_DEBUG_KMS("Unexpected DDC pin for port D\n");
+	}
+
+	if (is_dp) {
+		if (aux_channel == 0x40 && port != PORT_A)
+			DRM_DEBUG_KMS("Unexpected AUX channel for port A\n");
+		if (aux_channel == 0x10 && port != PORT_B)
+			DRM_DEBUG_KMS("Unexpected AUX channel for port B\n");
+		if (aux_channel == 0x20 && port != PORT_C)
+			DRM_DEBUG_KMS("Unexpected AUX channel for port C\n");
+		if (aux_channel == 0x30 && port != PORT_D)
+			DRM_DEBUG_KMS("Unexpected AUX channel for port D\n");
+	}
+
 	if (bdb->version >= 158) {
 		/* The VBT HDMI level shift values match the table we have. */
 		hdmi_level_shift = child->raw[7] & 0xF;