linux-kernel - Re: [PATCH v2 04/16] drm/panel/sun4i: Keep up with refcounting

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Message-ID: <20250624-invisible-khaki-hog-14f5a0@houat>
Date: Tue, 24 Jun 2025 10:53:02 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Anusha Srivatsa <asrivats@...hat.com>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <jessica.zhang@....qualcomm.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, 
	Jagan Teki <jagan@...rulasolutions.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Chen-Yu Tsai <wens@...e.org>, 
	Samuel Holland <samuel@...lland.org>, Seung-Woo Kim <sw0312.kim@...sung.com>, 
	Kyungmin Park <kyungmin.park@...sung.com>, Krzysztof Kozlowski <krzk@...nel.org>, 
	Alim Akhtar <alim.akhtar@...sung.com>, Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>, 
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>, Kieran Bingham <kieran.bingham+renesas@...asonboard.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Magnus Damm <magnus.damm@...il.com>, 
	Biju Das <biju.das.jz@...renesas.com>, Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
	Alain Volmat <alain.volmat@...s.st.com>, Raphael Gallais-Pou <rgallaispou@...il.com>, 
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	Linus Walleij <linus.walleij@...aro.org>, Thierry Reding <thierry.reding@...il.com>, 
	Mikko Perttunen <mperttunen@...dia.com>, Jonathan Hunter <jonathanh@...dia.com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev, linux-samsung-soc@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 04/16] drm/panel/sun4i: Keep up with refcounting

On Fri, Jun 20, 2025 at 03:54:10PM -0500, Anusha Srivatsa wrote:
> On Fri, Jun 20, 2025 at 8:27 AM Maxime Ripard <mripard@...nel.org> wrote:
> 
> > Hi,
> >
> > On Thu, Jun 19, 2025 at 02:15:56PM -0500, Anusha Srivatsa wrote:
> > > Put the panel reference back when driver is no
> > > longer using it.
> > >
> > > Signed-off-by: Anusha Srivatsa <asrivats@...hat.com>
> >
> > When I asked you to provide a rationale for why you think the
> > drm_panel_put() call belonged where it does, it was pretty obvious it
> > needed to be done for all patches with the same issue, not just a few
> > random ones.
>
> Well, not totally random. THe intention was to specifically explain
> the cases where the drm_panel_put() is part of a probe(), enable() or
> attach() like function since that caused confusion in the last
> version. There must have been misunderstanding on my end when I
> thought only those cases needed additional explanation. I will make
> the commit message more verbose.

Eventually, it's a memory management thing. You can't judge how a
driver, framework or function uses the memory from 3 lines of context.

This patch is a good example: it might make sense from the 3 lines of
context. But if you consider what this function is doing, and how it
uses the drm_panel pointer, what you did is broken.

Maxime

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