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

From: Laurent Pinchart <[email-masked]>
Date: Mon, 4 May 2026 17:55:36 +0300

On Mon, May 04, 2026 at 12:45:05PM +0200, Luca Ceresoli wrote:
> 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 <[email-masked]>
> Signed-off-by: Luca Ceresoli <[email-masked]>
> ---
> 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

s/graph presents/graph is present/

Reviewed-by: Laurent Pinchart <[email-masked]>

> +	 * 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)

-- 
Regards,

Laurent Pinchart