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).

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Maya Matuszczyk <maccraft123mc@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

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 +494,64 @@ 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);
+
+/**
+ * drm_of_get_dsi_bus - find the DSI bus for a given device
+ * @dev: parent device of display (SPI, I2C)
+ * @dsi_host: DSI host to be populated
+ * @info: DSI device info to be updated with correct DSI node
+ *
+ * Given a panel device parented to a non-DSI device, follow the
+ * devicetree to find the correct DSI host node and populate the
+ * dsi_host with the correct host and info with the correct node.
+ * Returns zero if successful, -EPROBE_DEFER if the DSI host is
+ * found but not available, or -ENODEV otherwise.
+ */
+int drm_of_get_dsi_bus(struct device *dev,
+			      struct mipi_dsi_host **dsi_host,
+			      struct mipi_dsi_device_info *info)
+{
+	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 -ENODEV;
+
+	/*
+	 * Follow the first endpoint to get the DSI host node.
+	 */
+	dsi_host_node = of_graph_get_remote_port_parent(endpoint);
+	if (!dsi_host_node)
+		goto error;
+
+	/*
+	 * 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)) {
+		of_node_put(endpoint);
+		return -EPROBE_DEFER;
+	}
+
+	/*
+	 * Set the node of the mipi_dsi_device_info to the correct node
+	 * and then release the endpoint node since we're done with it.
+	 */
+	info->node = of_graph_get_remote_port(endpoint);
+	if (IS_ERR_OR_NULL(info->node))
+		goto error;
+
+	of_node_put(endpoint);
+	return 0;
+
+error:
+	of_node_put(endpoint);
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(drm_of_get_dsi_bus);

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
@@ -56,6 +58,9 @@ int drm_of_get_data_lanes_count_ep(const struct device_node *port,
 				   int port_reg, int reg,
 				   const unsigned int min,
 				   const unsigned int max);
+int drm_of_get_dsi_bus(struct device *dev,
+		       struct mipi_dsi_host **dsi_host,
+		       struct mipi_dsi_device_info *info);
 #else
 static inline uint32_t drm_of_crtc_port_mask(struct drm_device *dev,
 					  struct device_node *port)
@@ -127,6 +132,12 @@ drm_of_get_data_lanes_count_ep(const struct device_node *port,
 {
 	return -EINVAL;
 }
+static int drm_of_get_dsi_bus(struct device *dev,
+			      struct mipi_dsi_host **dsi_host,
+			      struct mipi_dsi_device_info *info)
+{
+	return -EINVAL;
+}
 #endif
 
 /*