backend/drm: add support for panel orientation

Expose the panel orientation with wlr_drm_connector_get_panel_orientation.
Leave it to the compositor to consume this information and configure the
output accordingly.

Closes: https://github.com/swaywm/wlroots/issues/1581

backend/drm/drm.c

@@ -977,6 +977,37 @@ uint32_t wlr_drm_connector_get_id(struct wlr_output *output) {
 	return conn->id;
 }
 
+enum wl_output_transform wlr_drm_connector_get_panel_orientation(
+		struct wlr_output *output) {
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	if (conn->props.panel_orientation) {
+		return WL_OUTPUT_TRANSFORM_NORMAL;
+	}
+
+	char *orientation = get_drm_prop_enum(conn->backend->fd, conn->id,
+		conn->props.panel_orientation);
+	if (orientation == NULL) {
+		return WL_OUTPUT_TRANSFORM_NORMAL;
+	}
+
+	enum wl_output_transform tr;
+	if (strcmp(orientation, "Normal") == 0) {
+		tr = WL_OUTPUT_TRANSFORM_NORMAL;
+	} else if (strcmp(orientation, "Left Side Up") == 0) {
+		tr = WL_OUTPUT_TRANSFORM_90;
+	} else if (strcmp(orientation, "Upside Down") == 0) {
+		tr = WL_OUTPUT_TRANSFORM_180;
+	} else if (strcmp(orientation, "Right Side Up") == 0) {
+		tr = WL_OUTPUT_TRANSFORM_270;
+	} else {
+		wlr_drm_conn_log(conn, WLR_ERROR, "Unknown panel orientation: %s", orientation);
+		tr = WL_OUTPUT_TRANSFORM_NORMAL;
+	}
+
+	free(orientation);
+	return tr;
+}
+
 static const int32_t subpixel_map[] = {
 	[DRM_MODE_SUBPIXEL_UNKNOWN] = WL_OUTPUT_SUBPIXEL_UNKNOWN,
 	[DRM_MODE_SUBPIXEL_HORIZONTAL_RGB] = WL_OUTPUT_SUBPIXEL_HORIZONTAL_RGB,

backend/drm/properties.c

@@ -26,6 +26,7 @@ static const struct prop_info connector_info[] = {
 	{ "PATH", INDEX(path) },
 	{ "link-status", INDEX(link_status) },
 	{ "non-desktop", INDEX(non_desktop) },
+	{ "panel orientation", INDEX(panel_orientation) },
 	{ "subconnector", INDEX(subconnector) },
 	{ "vrr_capable", INDEX(vrr_capable) },
 #undef INDEX

include/backend/drm/properties.h

@@ -19,6 +19,7 @@ union wlr_drm_connector_props {
 		uint32_t vrr_capable; // not guaranteed to exist
 		uint32_t subconnector; // not guaranteed to exist
 		uint32_t non_desktop;
+		uint32_t panel_orientation; // not guaranteed to exist
 
 		// atomic-modesetting only
 

include/wlr/backend/drm.h

@@ -61,4 +61,15 @@ typedef struct _drmModeModeInfo drmModeModeInfo;
 struct wlr_output_mode *wlr_drm_connector_add_mode(struct wlr_output *output,
 	const drmModeModeInfo *mode);
 
+/**
+ * Get the connector's panel orientation.
+ *
+ * On some devices the panel is mounted in the casing in such a way that the
+ * top side of the panel does not match with the top side of the device. This
+ * function returns the output transform which needs to be applied to compensate
+ * for this.
+ */
+enum wl_output_transform wlr_drm_connector_get_panel_orientation(
+	struct wlr_output *output);
+
 #endif