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

From: "Luca Ceresoli" <[email-masked]>
Date: Mon, 04 May 2026 17:03:34 +0200

Hi Laurent,

On Mon May 4, 2026 at 4:55 PM CEST, Laurent Pinchart wrote:
> 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/

Oh, wow. I copied this comment from elsewhere, meaning the same typo is
there too. I'm taking a note to fix those too.

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

Thanks!

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com