drm/i915: add some assertions about VBT DDI port types

Our code makes a lot of assumptions regarding what each DDI port
actually supports, and the VBT should tell us what is really happening
in the hardware. So parse the information provided by the VBT and
check if any of our assumptions is wrong.

Our driver also has a history of not really trusting the VBT, so a
WARN here could mean that:
 a) our coding assumptions are wrong
 b) the VBT is wrong
 c) we're incorrectly parsing the VBT
 d) the checks are wrong

But I really hope we won't ever trigger any of those WARNs.

v2: Don't check the redundant "Capabilities" field from byte 24 since
    it doesn't seem to be used.
v3: Rebase
v4: Replace WARN with DRM_DEBUG_KMS
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com> (v2)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_bios.c

@@ -590,7 +590,7 @@ 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;
+	bool is_dvi, is_hdmi, is_dp, is_edp, is_crt;
 	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
@@ -628,6 +628,28 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
 
 	is_dvi = child->common.device_type & (1 << 4);
 	is_dp = child->common.device_type & (1 << 2);
+	is_crt = child->common.device_type & (1 << 0);
+	is_hdmi = is_dvi && (child->common.device_type & (1 << 11)) == 0;
+	is_edp = is_dp && (child->common.device_type & (1 << 12));
+
+	DRM_DEBUG_KMS("Port %c VBT info: DP:%d HDMI:%d DVI:%d EDP:%d CRT:%d\n",
+		      port_name(port), is_dp, is_hdmi, is_dvi, is_edp, is_crt);
+
+	if (is_edp && is_dvi)
+		DRM_DEBUG_KMS("Internal DP port %c is TMDS compatible\n",
+			      port_name(port));
+	if (is_crt && port != PORT_E)
+		DRM_DEBUG_KMS("Port %c is analog\n", port_name(port));
+	if (is_crt && (is_dvi || is_dp))
+		DRM_DEBUG_KMS("Analog port %c is also DP or TMDS compatible\n",
+			      port_name(port));
+	if (is_dvi && (port == PORT_A || port == PORT_E))
+		DRM_DEBUG_KMS("Port %c is TMDS compabile\n", port_name(port));
+	if (!is_dvi && !is_dp && !is_crt)
+		DRM_DEBUG_KMS("Port %c is not DP/TMDS/CRT compatible\n",
+			      port_name(port));
+	if (is_edp && (port == PORT_B || port == PORT_C || port == PORT_E))
+		DRM_DEBUG_KMS("Port %c is internal DP\n", port_name(port));
 
 	if (is_dvi) {
 		if (child->common.ddc_pin == 0x05 && port != PORT_B)