linux-kernel - Re: [PATCH v6 15/26] drm/bridge: devm_drm_of_get_bridge and drmm_of_get

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Message-ID: <k6endeznshwoftdmhyezuavg6vlemujukfybtqeil66cmjnhtv@yh6knwpabpno>
Date: Fri, 7 Feb 2025 21:57:30 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, 
	Jagan Teki <jagan@...rulasolutions.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, Daniel Thompson <danielt@...nel.org>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Jonathan Corbet <corbet@....net>, 
	Sam Ravnborg <sam@...nborg.org>, Boris Brezillon <bbrezillon@...nel.org>, 
	Nicolas Ferre <nicolas.ferre@...rochip.com>, Alexandre Belloni <alexandre.belloni@...tlin.com>, 
	Claudiu Beznea <claudiu.beznea@...on.dev>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Paul Kocialkowski <contact@...lk.fr>, Maxime Ripard <mripard@...nel.org>, 
	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>, 
	Hervé Codina <herve.codina@...tlin.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v6 15/26] drm/bridge: devm_drm_of_get_bridge and
 drmm_of_get_bridge: automatically put the bridge

On Fri, Feb 07, 2025 at 11:44:01AM +0100, Luca Ceresoli wrote:
> On Fri, 7 Feb 2025 05:17:43 +0200
> Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:
> 
> > On Thu, Feb 06, 2025 at 07:14:30PM +0100, Luca Ceresoli wrote:
> > > Add a devm/drmm action to these functions so the bridge reference is
> > > dropped automatically when the caller is removed.  
> > 
> > I think the get() should go to the underlying of_drm_bridge_find() function.
> 
> It is done in the following patch.
> 
> Indeed I could swap patches 15 and 16 for clarity. Or I could squash
> together patches 14+15+16, as they are various parts or the refcounted
> bridge implementation, but I felt like keeping them separated would
> help reviewing.

I think most of refcounting should be introduced as a single patch,
otherwise you risk having memory leaks or disappearing bridges.

> 
> > Also it really feels like it's an overkill to keep the wrappers. After
> > getting bridge being handled by the panel code would it be possible to
> > drop all of them?
> 
> Do you mean having only drm_of_get_bridge_by_node(), without any devm
> or drmm variant? I'm not sure it is a good idea. Most DRM code (well,
> all of it, technically) is currently unable of working with refcounted
> bridges, but if they use the devm variant they will put the ref when
> they disappear.
> 
> > Then this patch might introduce one new devm_
> > function? Or are drmm_ functions actually being used to store data in
> > the drmm-managed memory?
> 
> Which devm function are you thinking about? Sorry, I'm not following
> here.

drmm_of_get_bridge() / devm_of_get_bridge(). I have a feeling (which of
course might be wrong), that they were used somewhat randomly in some
cases.

> 
> Luca
> 
> -- 
> Luca Ceresoli, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

-- 
With best wishes
Dmitry