linux-kernel - Re: [PATCH v2 34/34] drm/bridge: panel: convert to devm_drm_bridge

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Message-ID: <20250428-wild-condor-of-defiance-cadf60@houat>
Date: Mon, 28 Apr 2025 13:39:23 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, 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>, Jagan Teki <jagan@...rulasolutions.com>, 
	Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, 
	Douglas Anderson <dianders@...omium.org>, Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
	Krzysztof Kozlowski <krzk@...nel.org>, Anusha Srivatsa <asrivats@...hat.com>, 
	Paul Kocialkowski <paulk@...-base.io>, Dmitry Baryshkov <lumag@...nel.org>, 
	Hui Pu <Hui.Pu@...ealthcare.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
	dri-devel@...ts.freedesktop.org, asahi@...ts.linux.dev, linux-kernel@...r.kernel.org, 
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	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 34/34] drm/bridge: panel: convert to
 devm_drm_bridge_alloc() API

On Thu, Apr 24, 2025 at 10:05:49PM +0200, Luca Ceresoli wrote:
> This is the new API for allocating DRM bridges.
> 
> The devm lifetime management of this driver is peculiar. The underlying
> device for the panel_bridge is the panel, and the devm lifetime is tied the
> panel device (panel->dev). However the panel_bridge allocation is not
> performed by the panel driver, but rather by a separate entity (typically
> the previous bridge in the encoder chain).
> 
> Thus when that separate entoty is destroyed, the panel_bridge is not
> removed automatically by devm, so it is rather done explicitly by calling
> drm_panel_bridge_remove(). This is the function that does devm_kfree() the
> panel_bridge in current code, so update it as well to put the bridge
> reference instead.
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

This looks fine, but we need a TODO entry to clean this up later on, and
a comment on devm_drm_put_bridge that this is inherently unsafe and
must not be used.

Maxime

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