linux-kernel - Re: [PATCH v7 05/11] drm/bridge: add a cleanup action for scope-based drm_bridge

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Message-ID: <20250314-banana-toucanet-of-masquerade-8eeb4e@houat>
Date: Fri, 14 Mar 2025 19:08:22 +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 05/11] drm/bridge: add a cleanup action for
 scope-based drm_bridge_put() invocation

On Fri, Mar 14, 2025 at 11:31:18AM +0100, Luca Ceresoli wrote:
> Many functions get a drm_bridge pointer, only use it in the function body
> (or a smaller scope such as a loop body), and don't store it. In these
> cases they always need to drm_bridge_put() it before returning (or exiting
> the scope).
> 
> Some of those functions have complex code paths with multiple return points
> or loop break/continue. This makes adding drm_bridge_put() in the right
> places tricky, ugly and error prone in case of future code changes.
> 
> Others use the bridge pointer in the return statement and would need to
> split the return line to fit the drm_bridge_put, which is a bit annoying:
> 
>   -return some_thing(bridge);
>   +ret = some_thing(bridge);
>   +drm_bridge_put(bridge);
>   +return ret;
> 
> To make it easier for all of them to put the bridge reference correctly
> without complicating code, define a scope-based cleanup action to be used
> with __free().
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> 
> ---
> 
> This patch was added in v7.
> ---
>  include/drm/drm_bridge.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 5c1e2b9cafb12eb429d1f5d3ef312e6cf9b54f47..a5accd64c364ebb57903ae1e7459034ad9ebf4f3 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -23,6 +23,7 @@
>  #ifndef __DRM_BRIDGE_H__
>  #define __DRM_BRIDGE_H__
>  
> +#include <linux/cleanup.h>
>  #include <linux/ctype.h>
>  #include <linux/list.h>
>  #include <linux/mutex.h>
> @@ -995,6 +996,9 @@ static inline struct drm_bridge *drm_bridge_put(struct drm_bridge *bridge)
>  	return bridge;
>  }
>  
> +/* Cleanup action for use with __free() */
> +DEFINE_FREE(drm_bridge_put, struct drm_bridge *, if (_T) drm_bridge_put(_T))
> +

IIRC, drm_bridge_put already checks for the pointer being null before
dereferencing it, right? Then we can probably simplify the macro here.

Either way,

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

Maxime

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