Re: [PATCH 01/10] drm/bridge: add of_drm_get_bridge_by_endpoint()

[Dmitry Baryshkov]

On Mon, Apr 13, 2026 at 03:58:33PM +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 slightly simpler to use: just takes no @panel parameter
>  - 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.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_bridge.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_bridge.h     |  9 +++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index ba80bebb5685..e51990b74417 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -1581,6 +1581,52 @@ 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
> + * @bridge: pointer to hold returned drm_bridge, must not be NULL
> + *
> + * 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 zero (and sets *bridge to a valid bridge pointer) if successful,
> + * or one of the standard error codes (and the value in *bridge is
> + * unspecified) if it fails.

Can we return drm_bridge or error cookie instead?

> + */
> +int of_drm_get_bridge_by_endpoint(const struct device_node *np,
> +				  int port, int endpoint,
> +				  struct drm_bridge **bridge)

Nit: can it be drm_of_get_bridge_by_endpoint?

> +{
> +	if (!bridge)
> +		return -EINVAL;
> +
> +	/*
> +	 * 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 -ENODEV;
> +
> +	struct device_node *remote __free(device_node) =
> +		of_graph_get_remote_node(np, port, endpoint);
> +	if (!remote)
> +		return -ENODEV;
> +
> +	*bridge = of_drm_find_and_get_bridge(remote);
> +	if (*bridge)
> +		return 0;
> +
> +	return -EPROBE_DEFER;
> +}
> +EXPORT_SYMBOL_GPL(of_drm_get_bridge_by_endpoint);
>  #endif
>  

-- 
With best wishes
Dmitry