linux-kernel - Re: Re: [PATCH v1 2/3] media: cedrus: Set the platform driver data earlier

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Date:   Thu, 25 Aug 2022 23:04:50 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     linux-media@...r.kernel.org, Maxime Ripard <mripard@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     kernel@...labora.com, stable@...r.kernel.org,
        linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH v1 2/3] media: cedrus: Set the platform driver data earlier

Dne nedelja, 21. avgust 2022 ob 22:40:21 CEST je Dmitry Osipenko napisal(a):
> On 8/20/22 11:25, Jernej Škrabec wrote:
> > Dne petek, 19. avgust 2022 ob 17:37:20 CEST je Nicolas Dufresne 
napisal(a):
> >> Le vendredi 19 août 2022 à 06:17 +0200, Jernej Škrabec a écrit :
> >>> Dne četrtek, 18. avgust 2022 ob 22:33:07 CEST je Nicolas Dufresne
> > 
> > napisal(a):
> >>>> From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> >>>> 
> >>>> The cedrus_hw_resume() crashes with NULL deference on driver probe if
> >>>> runtime PM is disabled because it uses platform data that hasn't been
> >>>> set up yet. Fix this by setting the platform data earlier during probe.
> >>> 
> >>> Does it even work without PM? Maybe it would be better if Cedrus would
> >>> select PM in Kconfig.
> >> 
> >> I cannot comment myself on this, but it does not seem to invalidate this
> >> Dmitry's fix.
> > 
> > If NULL pointer dereference happens only when PM is disabled, then it
> > does. I have PM always enabled and I never experienced above issue.
> 
> Originally this fix was needed when I changed cedrus_hw_probe() to do
> the rpm-resume while was debugging the hang issue and then also noticed
> that the !PM should be broken. It's a good common practice for all
> drivers to have the drv data set early to avoid such problems, hence it
> won't hurt to make this change anyways.

Ok, as others pointed out, this is still a good thing, so:

Acked-by: Jernej Skrabec <jernej.skrabec@...il.com>


> 
> In practice nobody disables PM other than for debugging purposes and !PM
> handling is often broken in drivers. I assume that it might be even
> better to enable PM for all Allwiner SoCs and remove !PM handling from
> all the affected drivers, like it was done for Tegra some time ago.
> 

Maybe in the future :)

Best regards,
Jernej

> --
> Best regards,
> Dmitry