linux-kernel - Re: [PATCH v7 06/11] drm/bridge: get the bridge returned by drm_bridge_chain_get_first

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Message-ID: <20250314-aspiring-myrtle-husky-a5f4ac@houat>
Date: Fri, 14 Mar 2025 19:10:41 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Marek Vasut <marex@...x.de>, Stefan Agner <stefan@...er.ch>, 
	Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, 
	Inki Dae <inki.dae@...sung.com>, Jagan Teki <jagan@...rulasolutions.com>, 
	Marek Szyprowski <m.szyprowski@...sung.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
	Anusha Srivatsa <asrivats@...hat.com>, Paul Kocialkowski <paulk@...-base.io>, 
	Dmitry Baryshkov <lumag@...nel.org>, Hervé Codina <herve.codina@...tlin.com>, 
	Hui Pu <Hui.Pu@...ealthcare.com>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 06/11] drm/bridge: get the bridge returned by
 drm_bridge_chain_get_first_bridge()

On Fri, Mar 14, 2025 at 11:31:19AM +0100, Luca Ceresoli wrote:
> drm_bridge_chain_get_first_bridge() returns a bridge pointer that the
> caller could hold for a long time. Increment the refcount of the returned
> bridge and document it must be put by the caller.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> 
> ---
> 
> This patch was added in v7.
> ---
>  include/drm/drm_bridge.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index a5accd64c364ebb57903ae1e7459034ad9ebf4f3..d9777d5f2e9ef006f0062e4507bce99df4146cd9 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -1105,6 +1105,9 @@ drm_bridge_get_prev_bridge(struct drm_bridge *bridge)
>   * drm_bridge_chain_get_first_bridge() - Get the first bridge in the chain
>   * @encoder: encoder object
>   *
> + * The refcount of the returned bridge is incremented. Use drm_bridge_put()
> + * when done with it.
> + *
>   * RETURNS:
>   * the first bridge in the chain, or NULL if @encoder has no bridge attached
>   * to it.
> @@ -1112,8 +1115,8 @@ drm_bridge_get_prev_bridge(struct drm_bridge *bridge)
>  static inline struct drm_bridge *
>  drm_bridge_chain_get_first_bridge(struct drm_encoder *encoder)
>  {
> -	return list_first_entry_or_null(&encoder->bridge_chain,
> -					struct drm_bridge, chain_node);
> +	return drm_bridge_get(list_first_entry_or_null(&encoder->bridge_chain,
> +						       struct drm_bridge, chain_node));
>  }

We'll need to modify drm_bridge_get_next_bridge, drm_bridge_get_prev_bridge, and
drm_for_each_bridge_in_chain in a similar manner, but for this one

Reviewed-by: Maxime Ripard <mripard@...nel.org>

Maxime

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