Re: [PATCH 06/26] drm/bridge: add devm_drm_of_find_bridge

[Louis Chauvet]

On 11/19/25 13:05, Luca Ceresoli wrote:
Several drivers (about 20) follow the same pattern:

  1. get a pointer to a bridge (typically the next bridge in the chain) by
     calling of_drm_find_bridge()
  2. store the returned pointer in the private driver data, keep it until
     driver .remove
  3. dereference the pointer at attach time and possibly at other times

of_drm_find_bridge() is now deprecated because it does not increment the
refcount and should be replaced with drm_of_find_bridge() +
drm_bridge_put().

However some of those drivers have a complex code flow and adding a
drm_bridge_put() call in all the appropriate locations is error-prone,
leads to ugly and more complex code, and can lead to errors over time with
code flow changes.

To handle all those drivers in a straightforward way, add a devm variant of
drm_of_find_bridge() that adds a devm action to invoke drm_bridge_put()
when the said driver is removed. This allows all those drivers to put the
reference automatically and safely with a one line change:

   - priv->next_bridge = of_drm_find_bridge(remote_np);
   + priv->next_bridge = devm_drm_of_find_bridge(dev, remote_np);

Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com>
---
  drivers/gpu/drm/drm_bridge.c | 30 ++++++++++++++++++++++++++++++
  include/drm/drm_bridge.h     |  5 +++++
  2 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 09ad825f9cb8..c7baafbe5695 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -1446,6 +1446,36 @@ struct drm_bridge *drm_of_find_bridge(struct device_node 
*np)
  }
  EXPORT_SYMBOL(drm_of_find_bridge);
  
+/**
+ * devm_drm_of_find_bridge - find the bridge corresponding to the device
+ *                          node in the global bridge list and add a devm
+ *                          action to put it
+ *
+ * @dev: device requesting the bridge
+ * @np: device node
+ *
+ * On success the returned bridge refcount is incremented, and a devm
+ * action is added to call drm_bridge_put() when @dev is removed. So the
+ * caller does not have to put the returned bridge explicitly.
+ *
+ * RETURNS:
+ * drm_bridge control struct on success, NULL on failure

I am not sure for the "NULL on failure", you return ERR_PTR(err), which 
is probably not NULL but an error code.

+ */
+struct drm_bridge *devm_drm_of_find_bridge(struct device *dev, struct 
device_node *np)
+{
+       struct drm_bridge *bridge = drm_of_find_bridge(np);
+
+       if (bridge) {
+               int err = devm_add_action_or_reset(dev, drm_bridge_put_void, 
bridge);
+
+               if (err)
+                       return ERR_PTR(err);
+       }
+
+       return bridge;
+}
+EXPORT_SYMBOL(devm_drm_of_find_bridge);
+
  /**
   * of_drm_find_bridge - find the bridge corresponding to the device node in
   *                    the global bridge list
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index e74e91004c48..98d5433f7d35 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -1314,12 +1314,17 @@ int drm_bridge_attach(struct drm_encoder *encoder, 
struct drm_bridge *bridge,
  
  #ifdef CONFIG_OF
  struct drm_bridge *drm_of_find_bridge(struct device_node *np);
+struct drm_bridge *devm_drm_of_find_bridge(struct device *dev, struct 
device_node *np);
  struct drm_bridge *of_drm_find_bridge(struct device_node *np);
  #else
  static inline struct drm_bridge *drm_of_find_bridge(struct device_node *np)
  {
        return NULL;
  }
+static inline struct drm_bridge *devm_drm_of_find_bridge(struct device *dev, 
struct device_node *np)
+{
+       return NULL;
+}
  static inline struct drm_bridge *of_drm_find_bridge(struct device_node *np)
  {
        return NULL;