Message-ID: <35bda203-8c15-4219-a231-1379f909229f@bootlin.com>
Date: Wed, 19 Nov 2025 14:22:21 +0000
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
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Cc: Hui Pu <Hui.Pu@...ealthcare.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
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 linux-arm-kernel@...ts.infradead.org, linux-renesas-soc@...r.kernel.org,
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 linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 01/26] drm/bridge: add drm_of_find_bridge()



On 11/19/25 13:05, Luca Ceresoli wrote:
> of_drm_find_bridge() does not increment the refcount for the returned
> bridge, but that is required now. However converting it and all its users
> is not realistically doable at once given the large amount of (direct and
> indirect) callers and the complexity of some. Also, "of_drm_find_bridge is
> oddly named according to our convention and it would make more sense to be
> called drm_of_find_bridge()" (quoted from Link: below).
> 
> Solve both issues by creating a new drm_of_find_bridge() that is identical
> to of_drm_find_bridge() except it takes a reference. Then
> of_drm_find_bridge() will be deprecated to be eventually removed.
> 
> Suggested-by: Maxime Ripard <mripard@...nel.org>
> Link: https://lore.kernel.org/dri-devel/20250319-stylish-lime-mongoose-0a18ad@houat/
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> 
> ---
> 
> Note: a simple implementation would just be
>    { return drm_bridge_get(of_drm_find_bridge(np)); }
> but it would release the mutex before getting the reference, so it is
> not safe. Make things simple by duplicating the code. A later patch will
> make instead the (to be deprecated) of_drm_find_bridge() become a wrapper
> of the new drm_of_find_bridge()
> ---
>   drivers/gpu/drm/drm_bridge.c | 29 +++++++++++++++++++++++++++++
>   include/drm/drm_bridge.h     |  5 +++++
>   2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 8f355df883d8..d98a7b4a83c0 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -1417,6 +1417,35 @@ void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>   EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
>   
>   #ifdef CONFIG_OF
> +/**
> + * drm_of_find_bridge - find the bridge corresponding to the device node in
> + *			the global bridge list
> + * @np: device node
> + *
> + * The refcount of the returned bridge is incremented. Use drm_bridge_put()
> + * when done with it.
> + *
> + * RETURNS:
> + * drm_bridge control struct on success, NULL on failure
> + */
> +struct drm_bridge *drm_of_find_bridge(struct device_node *np)
> +{
> +	struct drm_bridge *bridge;
> +
> +	mutex_lock(&bridge_lock);
> +
> +	list_for_each_entry(bridge, &bridge_list, list) {
> +		if (bridge->of_node == np) {
> +			mutex_unlock(&bridge_lock);

It seems a bit strange to unlock the mutex just before the 
drm_bridge_get, is it expected?

If no, I think you can use scoped_guard(mutex, &bridge_lock) to avoid 
messing with mutex_unlock, IIRC, scoped_guard will unlock the mutex just 
after the return, so in your case, just after the drm_bridge_get.

> +			return drm_bridge_get(bridge);
> +		}
> +	}
> +
> +	mutex_unlock(&bridge_lock);
> +	return NULL;
> +}
> +EXPORT_SYMBOL(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 0ff7ab4aa868..e74e91004c48 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -1313,8 +1313,13 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>   		      enum drm_bridge_attach_flags flags);
>   
>   #ifdef CONFIG_OF
> +struct drm_bridge *drm_of_find_bridge(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 *of_drm_find_bridge(struct device_node *np)
>   {
>   	return NULL;
> 

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