drm/radeon/kms: don't crash if no DDC bus on VGA/DVI connector.

This is strange - like really really strange, twilight zone of strange.
VGA ports have DDC buses, but sometimes for some reasons the BIOS
says we don't and we oops - AMD mentioned bios bugs so we'll have
to add quirks.

reported on irc by nirbheek and
https://bugzilla.redhat.com/show_bug.cgi?id=554323Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_connectors.c

@@ -580,16 +580,18 @@ static enum drm_connector_status radeon_vga_detect(struct drm_connector *connect
 	struct radeon_connector *radeon_connector = to_radeon_connector(connector);
 	struct drm_encoder *encoder;
 	struct drm_encoder_helper_funcs *encoder_funcs;
-	bool dret;
+	bool dret = false;
 	enum drm_connector_status ret = connector_status_disconnected;
 
 	encoder = radeon_best_single_encoder(connector);
 	if (!encoder)
 		ret = connector_status_disconnected;
 
+	if (radeon_connector->ddc_bus) {
 		radeon_i2c_do_lock(radeon_connector->ddc_bus, 1);
 		dret = radeon_ddc_probe(radeon_connector);
 		radeon_i2c_do_lock(radeon_connector->ddc_bus, 0);
+	}
 	if (dret) {
 		if (radeon_connector->edid) {
 			kfree(radeon_connector->edid);
@@ -740,11 +742,13 @@ static enum drm_connector_status radeon_dvi_detect(struct drm_connector *connect
 	struct drm_mode_object *obj;
 	int i;
 	enum drm_connector_status ret = connector_status_disconnected;
-	bool dret;
+	bool dret = false;
 
+	if (radeon_connector->ddc_bus) {
 		radeon_i2c_do_lock(radeon_connector->ddc_bus, 1);
 		dret = radeon_ddc_probe(radeon_connector);
 		radeon_i2c_do_lock(radeon_connector->ddc_bus, 0);
+	}
 	if (dret) {
 		if (radeon_connector->edid) {
 			kfree(radeon_connector->edid);

drivers/gpu/drm/radeon/radeon_display.c

@@ -278,7 +278,7 @@ static void radeon_print_display_setup(struct drm_device *dev)
 		DRM_INFO("  %s\n", connector_names[connector->connector_type]);
 		if (radeon_connector->hpd.hpd != RADEON_HPD_NONE)
 			DRM_INFO("  %s\n", hpd_names[radeon_connector->hpd.hpd]);
-		if (radeon_connector->ddc_bus)
+		if (radeon_connector->ddc_bus) {
 			DRM_INFO("  DDC: 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x 0x%x\n",
 				 radeon_connector->ddc_bus->rec.mask_clk_reg,
 				 radeon_connector->ddc_bus->rec.mask_data_reg,
@@ -288,6 +288,15 @@ static void radeon_print_display_setup(struct drm_device *dev)
 				 radeon_connector->ddc_bus->rec.en_data_reg,
 				 radeon_connector->ddc_bus->rec.y_clk_reg,
 				 radeon_connector->ddc_bus->rec.y_data_reg);
+		} else {
+			if (connector->connector_type == DRM_MODE_CONNECTOR_VGA ||
+			    connector->connector_type == DRM_MODE_CONNECTOR_DVII ||
+			    connector->connector_type == DRM_MODE_CONNECTOR_DVID ||
+			    connector->connector_type == DRM_MODE_CONNECTOR_DVIA ||
+			    connector->connector_type == DRM_MODE_CONNECTOR_HDMIA ||
+			    connector->connector_type == DRM_MODE_CONNECTOR_HDMIB)
+				DRM_INFO("  DDC: no ddc bus - possible BIOS bug - please report to xorg-driver-ati@lists.x.org\n");
+		}
 		DRM_INFO("  Encoders:\n");
 		list_for_each_entry(encoder, &dev->mode_config.encoder_list, head) {
 			radeon_encoder = to_radeon_encoder(encoder);