[PATCH v4 02/11] drm/bridge: add of_drm_get_bridge_by_endpoint()

Luca Ceresoli
2026-05-04T10:45:29Z

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>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Changes in v4:
- update function declaration in non-OF case

Changes in v2:
- return the bridge in the return value, not a double pointer
---
drivers/gpu/drm/drm_bridge.c | 41 +++++++++++++++++++++++++++++++++++++++++
include/drm/drm_bridge.h | 7 +++++++
2 files changed, 48 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 6fb71de6d22a..01f9e0426648 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -1582,6 +1582,47 @@ struct drm_bridge *of_drm_find_bridge(struct device_node *np)
return bridge;
}
EXPORT_SYMBOL(of_drm_find_bridge);
+
+/**
+ * of_drm_get_bridge_by_endpoint - return DRM bridge connected to a port/endpoint
+ * @np: device tree node containing output ports
+ * @port: port in the device tree node, or -1 for the first port found
+ * @endpoint: endpoint in the device tree node, or -1 for the first endpoint found
+ *
+ * Given a DT node's port and endpoint number, find the connected node and
+ * return the associated drm_bridge device.
+ *
+ * The refcount of the returned bridge is incremented. Use drm_bridge_put()
+ * when done with it.
+ *
+ * Returns a pointer to the connected drm_bridge, or a negative error on failure
+ */
+struct drm_bridge *of_drm_get_bridge_by_endpoint(const struct device_node *np,
+ int port, int endpoint)
+{
+ struct drm_bridge *bridge;
+
+ /*
+ * of_graph_get_remote_node() produces a noisy error message if port
+ * node isn't found and the absence of the port is a legit case here,
+ * so at first we silently check whether graph presents in the
+ * device-tree node.
+ */
+ if (!of_graph_is_present(np))
+ return ERR_PTR(-ENODEV);
+
+ struct device_node *remote __free(device_node) =
+ of_graph_get_remote_node(np, port, endpoint);
+ if (!remote)
+ return ERR_PTR(-ENODEV);
+
+ bridge = of_drm_find_and_get_bridge(remote);
+ if (!bridge)
+ return ERR_PTR(-EPROBE_DEFER);
+
+ return bridge;
+}
+EXPORT_SYMBOL_GPL(of_drm_get_bridge_by_endpoint);
#endif

/**
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index d6cd0f5af045..31e11a360c42 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 -ENODEV;
+}
#endif

static inline bool drm_bridge_is_last(struct drm_bridge *bridge)

--
2.53.0