drm/bridge: add of_drm_get_bridge_by_endpoint()

drm_of_find_panel_or_bridge() is widely used, but many callers pass NULL
into the @panel or the @bridge arguments, thus making a very partial usage
of this rather complex function.

Besides, the bridge returned in @bridge is not refcounted, thus making this
API unsafe when DRM bridge hotplug will be introduced.

Solve both issues for the cases of calls to drm_of_find_panel_or_bridge()
with a NULL @panel pointer by adding a new function that only looks for
bridges (and is thus much simpler) and increments the refcount of the
returned bridge.

The new function is identical to drm_of_find_panel_or_bridge() except it:

 - handles bridge refcounting: uses of_drm_find_and_get_bridge() instead of
   of_drm_find_bridge() internally to return a refcounted bridge
 - is simpler to use: just takes no @panel parameter, returns the pointer
   in the return value instead of a double pointer argument
 - has a simpler implementation: it is equal to
   drm_of_find_panel_or_bridge() after removing the code that becomes dead
   when @panel == NULL

Also add this function to drm_bridge.c and not drm_of.c because it returns
bridges only.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://patch.msgid.link/20260511-drm-bridge-alloc-getput-panel_or_bridge-v6-2-f61c9e498b3f@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index fdac9a526f38..4ba3a5deef9a 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -1327,6 +1327,8 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
 #ifdef CONFIG_OF
 struct drm_bridge *of_drm_find_and_get_bridge(struct device_node *np);
 struct drm_bridge *of_drm_find_bridge(struct device_node *np);
+struct drm_bridge *of_drm_get_bridge_by_endpoint(const struct device_node *np,
+						 int port, int endpoint);
 #else
 static inline struct drm_bridge *of_drm_find_and_get_bridge(struct device_node *np)
 {
@@ -1336,6 +1338,11 @@ static inline struct drm_bridge *of_drm_find_bridge(struct device_node *np)
 {
 	return NULL;
 }
+static inline struct drm_bridge *of_drm_get_bridge_by_endpoint(const struct device_node *np,
+							       int port, int endpoint)
+{
+	return ERR_PTR(-ENODEV);
+}
 #endif
 
 static inline bool drm_bridge_is_last(struct drm_bridge *bridge)