Message-ID: <f902bafa-6102-4a8c-a74f-48e3975e8ffd@bootlin.com>
Date: Mon, 7 Apr 2025 11:50:43 +0200
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>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, 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>
Cc: 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 v9 0/5] drm/bridge: add devm_drm_bridge_alloc() with
 bridge refcount



Le 26/03/2025 à 18:47, Luca Ceresoli a écrit :
> This series improves the way DRM bridges are allocated and initialized and
> makes them reference-counted. The goal of reference counting is to avoid
> use-after-free by drivers which got a pointer to a bridge and keep it
> stored and used even after the bridge has been deallocated.
> 
> The overall goal is supporting Linux devices with a DRM pipeline whose
> final components can be hot-plugged and hot-unplugged, including one or
> more bridges. For more details see the big picture [0].
> 
> DRM bridge drivers will have to be adapted to the new API -- the change is
> trivial for most cases. This series converts two of them to serve as an
> example. The remaining ones will be done as a follow-up after this first
> part is merged.
> 
> After that, refcounting will have to be added on the two sides: all
> functions returning a bridge pointer and all code obtaining such a
> pointer. A few examples have been sent in v7 (link below), they are OK, but
> I removed them since v8 because they must be merged only after converting
> all bridges.
> 
> Here's the grand plan:
> 
>   A. add new alloc API and refcounting (this series, at least patches 1-3)
>   B. after (A), convert all bridge drivers to new API
>   C. after (A), add documentation and kunit tests
>   D. after (B), add get/put to drm_bridge_add/remove() + attach/detech()
>      (patches 3-4 in the v7 series)
>   E. after (B), convert accessors (including patches 5-9 in the v7 series
>      which convert drm_bridge_chain_get_first_bridge() and its users);
>      this is a large work and can be done in chunks
>   F. after (A), debugfs: show refcount, show removed bridges
>   
> Layout of this:
> 
>   1. Add the new API and refcounting:
> 
>      drm/bridge: add devm_drm_bridge_alloc()
>      drm/bridge: add support for refcounting
>      drm/bridge: deprecate old-style bridge allocation
> 
>   2. convert a few bridge drivers (bridge providers) to the new API:
> 
>      drm/bridge: ti-sn65dsi83: use dynamic lifetime management
>      drm/bridge: samsung-dsim: use dynamic lifetime management
> 
> [0] https://lore.kernel.org/dri-devel/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/
> 
> Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
Applied on drm-misc-next, thanks!

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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