drm: of: Add drm_of_get_dsi_bus helper function

Add helper function to find DSI host for devices where DSI panel is not
a minor of a DSI bus (such as the Samsung AMS495QA01 panel or the
official Raspberry Pi touchscreen display).
Co-developed-by: Maya Matuszczyk <maccraft123mc@gmail.com>
Signed-off-by: Maya Matuszczyk <maccraft123mc@gmail.com>
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230123154603.1315112-2-macroalpha82@gmail.com

drivers/gpu/drm/drm_of.c

@@ -10,6 +10,7 @@
 #include <drm/drm_crtc.h>
 #include <drm/drm_device.h>
 #include <drm/drm_encoder.h>
+#include <drm/drm_mipi_dsi.h>
 #include <drm/drm_of.h>
 #include <drm/drm_panel.h>
 
@@ -493,3 +494,53 @@ int drm_of_get_data_lanes_count_ep(const struct device_node *port,
 	return ret;
 }
 EXPORT_SYMBOL_GPL(drm_of_get_data_lanes_count_ep);
+
+#if IS_ENABLED(CONFIG_DRM_MIPI_DSI)
+
+/**
+ * drm_of_get_dsi_bus - find the DSI bus for a given device
+ * @dev: parent device of display (SPI, I2C)
+ *
+ * Gets parent DSI bus for a DSI device controlled through a bus other
+ * than MIPI-DCS (SPI, I2C, etc.) using the Device Tree.
+ *
+ * Returns pointer to mipi_dsi_host if successful, -EINVAL if the
+ * request is unsupported, -EPROBE_DEFER if the DSI host is found but
+ * not available, or -ENODEV otherwise.
+ */
+struct mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev)
+{
+	struct mipi_dsi_host *dsi_host;
+	struct device_node *endpoint, *dsi_host_node;
+
+	/*
+	 * Get first endpoint child from device.
+	 */
+	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
+	if (!endpoint)
+		return ERR_PTR(-ENODEV);
+
+	/*
+	 * Follow the first endpoint to get the DSI host node and then
+	 * release the endpoint since we no longer need it.
+	 */
+	dsi_host_node = of_graph_get_remote_port_parent(endpoint);
+	of_node_put(endpoint);
+	if (!dsi_host_node)
+		return ERR_PTR(-ENODEV);
+
+	/*
+	 * Get the DSI host from the DSI host node. If we get an error
+	 * or the return is null assume we're not ready to probe just
+	 * yet. Release the DSI host node since we're done with it.
+	 */
+	dsi_host = of_find_mipi_dsi_host_by_node(dsi_host_node);
+	of_node_put(dsi_host_node);
+	if (IS_ERR_OR_NULL(dsi_host))
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return dsi_host;
+}
+EXPORT_SYMBOL_GPL(drm_of_get_dsi_bus);
+
+#endif /* CONFIG_DRM_MIPI_DSI */

include/drm/drm_of.h

@@ -15,6 +15,8 @@ struct drm_encoder;
 struct drm_panel;
 struct drm_bridge;
 struct device_node;
+struct mipi_dsi_device_info;
+struct mipi_dsi_host;
 
 /**
  * enum drm_lvds_dual_link_pixels - Pixel order of an LVDS dual-link connection
@@ -129,6 +131,16 @@ drm_of_get_data_lanes_count_ep(const struct device_node *port,
 }
 #endif
 
+#if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_MIPI_DSI)
+struct mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev);
+#else
+static inline struct
+mipi_dsi_host *drm_of_get_dsi_bus(struct device *dev)
+{
+	return ERR_PTR(-EINVAL);
+}
+#endif /* CONFIG_OF && CONFIG_DRM_MIPI_DSI */
+
 /*
  * drm_of_panel_bridge_remove - remove panel bridge
  * @np: device tree node containing panel bridge output ports