drm/i915/vbt: split out defaults that are set when there is no VBT

The main thing are the DDI ports. If there's a VBT that says there are
no outputs, we should trust that, and not have semi-random
defaults. Unfortunately, the defaults have resulted in some Chromebooks
without VBT to rely on this behaviour, so we split out the defaults for
the missing VBT case.

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/95c26079ff640d43f53b944f17e9fc356b36daec.1489152288.git.jani.nikula@intel.com

drivers/gpu/drm/i915/intel_bios.c

@@ -1341,6 +1341,7 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
 	return;
 }
 
+/* Common defaults which may be overridden by VBT. */
 static void
 init_vbt_defaults(struct drm_i915_private *dev_priv)
 {
@@ -1377,6 +1378,18 @@ init_vbt_defaults(struct drm_i915_private *dev_priv)
 			&dev_priv->vbt.ddi_port_info[port];
 
 		info->hdmi_level_shift = HDMI_LEVEL_SHIFT_UNKNOWN;
+	}
+}
+
+/* Defaults to initialize only if there is no VBT. */
+static void
+init_vbt_missing_defaults(struct drm_i915_private *dev_priv)
+{
+	enum port port;
+
+	for (port = PORT_A; port < I915_MAX_PORTS; port++) {
+		struct ddi_vbt_port_info *info =
+			&dev_priv->vbt.ddi_port_info[port];
 
 		info->supports_dvi = (port != PORT_A && port != PORT_E);
 		info->supports_hdmi = info->supports_dvi;
@@ -1516,8 +1529,10 @@ void intel_bios_init(struct drm_i915_private *dev_priv)
 	parse_ddi_ports(dev_priv, bdb);
 
 out:
-	if (!vbt)
+	if (!vbt) {
 		DRM_INFO("Failed to find VBIOS tables (VBT)\n");
+		init_vbt_missing_defaults(dev_priv);
+	}
 
 	if (bios)
 		pci_unmap_rom(pdev, bios);