drm/bridge: Add a function to abstract away panels

Display drivers so far need to have a lot of boilerplate to first
retrieve either the panel or bridge that they are connected to using
drm_of_find_panel_or_bridge(), and then either deal with each with ad-hoc
functions or create a drm panel bridge through drm_panel_bridge_add.

In order to reduce the boilerplate and hopefully create a path of least
resistance towards using the DRM panel bridge layer, let's create the
function devm_drm_of_get_bridge() to reduce that boilerplate.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210910130941.1740182-2-maxime@cerno.tech

drivers/gpu/drm/drm_bridge.c

@@ -28,6 +28,7 @@
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_bridge.h>
 #include <drm/drm_encoder.h>
+#include <drm/drm_of.h>
 #include <drm/drm_print.h>
 
 #include "drm_crtc_internal.h"
@@ -51,10 +52,8 @@
  *
  * Display drivers are responsible for linking encoders with the first bridge
  * in the chains. This is done by acquiring the appropriate bridge with
- * of_drm_find_bridge() or drm_of_find_panel_or_bridge(), or creating it for a
+ * devm_drm_of_get_bridge(). Once acquired, the bridge shall be attached to the
- * panel with drm_panel_bridge_add_typed() (or the managed version
+ * encoder with a call to drm_bridge_attach().
- * devm_drm_panel_bridge_add_typed()). Once acquired, the bridge shall be
- * attached to the encoder with a call to drm_bridge_attach().
  *
  * Bridges are responsible for linking themselves with the next bridge in the
  * chain, if any. This is done the same way as for encoders, with the call to
@@ -1233,6 +1232,40 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np)
 	return NULL;
 }
 EXPORT_SYMBOL(of_drm_find_bridge);
+
+/**
+ * devm_drm_of_get_bridge - Return next bridge in the chain
+ * @dev: device to tie the bridge lifetime to
+ * @np: device tree node containing encoder output ports
+ * @port: port in the device tree node
+ * @endpoint: endpoint in the device tree node
+ *
+ * Given a DT node's port and endpoint number, finds the connected node
+ * and returns the associated bridge if any, or creates and returns a
+ * drm panel bridge instance if a panel is connected.
+ *
+ * Returns a pointer to the bridge if successful, or an error pointer
+ * otherwise.
+ */
+struct drm_bridge *devm_drm_of_get_bridge(struct device *dev,
+					  struct device_node *np,
+					  u32 port, u32 endpoint)
+{
+	struct drm_bridge *bridge;
+	struct drm_panel *panel;
+	int ret;
+
+	ret = drm_of_find_panel_or_bridge(np, port, endpoint,
+					  &panel, &bridge);
+	if (ret)
+		return ERR_PTR(ret);
+
+	if (panel)
+		bridge = devm_drm_panel_bridge_add(dev, panel);
+
+	return bridge;
+}
+EXPORT_SYMBOL(devm_drm_of_get_bridge);
 #endif
 
 MODULE_AUTHOR("Ajay Kumar <ajaykumar.rs@samsung.com>");

drivers/gpu/drm/drm_of.c

@@ -231,6 +231,9 @@ EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
  * return either the associated struct drm_panel or drm_bridge device. Either
  * @panel or @bridge must not be NULL.
  *
+ * This function is deprecated and should not be used in new drivers. Use
+ * devm_drm_of_get_bridge() instead.
+ *
  * Returns zero if successful, or one of the standard error codes if it fails.
  */
 int drm_of_find_panel_or_bridge(const struct device_node *np,

include/drm/drm_bridge.h

@@ -911,6 +911,8 @@ struct drm_bridge *devm_drm_panel_bridge_add(struct device *dev,
 struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
 						   struct drm_panel *panel,
 						   u32 connector_type);
+struct drm_bridge *devm_drm_of_get_bridge(struct device *dev, struct device_node *node,
+					  u32 port, u32 endpoint);
 struct drm_connector *drm_panel_bridge_connector(struct drm_bridge *bridge);
 #endif