linux-kernel - Re: [PATCH] gpiolib: fix allocation of mixed dynamic/static GPIOs

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Date:   Thu, 27 Apr 2023 13:46:01 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "brgl@...ev.pl" <brgl@...ev.pl>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        ": Tony Lindgren" <tony@...mide.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: fix allocation of mixed dynamic/static GPIOs

On Thu, Apr 27, 2023 at 1:37 PM Andreas Kemnade <andreas@...nade.info> wrote:
>
> On Thu, 27 Apr 2023 06:20:34 +0000
> Christophe Leroy <christophe.leroy@...roup.eu> wrote:
>
> > Le 27/04/2023 à 08:00, Andy Shevchenko a écrit :
> > > On Thu, Apr 27, 2023 at 8:40 AM Christophe Leroy
> > > <christophe.leroy@...roup.eu> wrote:
> > >>
> > >>
> > >>
> > >> Le 27/04/2023 à 00:03, Andreas Kemnade a écrit :
> > >>> [Vous ne recevez pas souvent de courriers de andreas@...nade.info. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> > >>>
> > >>> If static allocation and dynamic allocation GPIOs are present,
> > >>> dynamic allocation pollutes the numberspace for static allocation,
> > >>> causing static allocation to fail.
> > >>> Enfore dynamic allocation above GPIO_DYNAMIC_BASE.
> > >>
> > >> Hum ....
> > >>
> > >> Commit 7b61212f2a07 ("gpiolib: Get rid of ARCH_NR_GPIOS") was supposed
> > >> to enforce dynamic allocation above GPIO_DYNAMIC_BASE already.
> > >>
> > >> Can you describe what is going wrong exactly with the above commit ?
> > >
> > > Above commit only works to the first dynamic allocation, if you need
> > > more than one with static ones present it mistakenly will give you a
> > > base _below_ DYNAMIC_BASE.
> >
> > Ah right, that needs to be fixed.
> >
> > >
> > > However, this change is just PoC I proposed, the conditional and
> > > action should be slightly different to cover a corner case, when
> > > statically allocated chip overlaps the DYNAMIC_BASE, i.e. gdev->base <
> > > DYNAMIC_BASE, while gdev->base + gdev->ngpio >= DYNAMIC_BASE.
> > >
> >
> > Yes you are right, that's gdev->base + gdev->ngpio that should be checked.
> >
> and that not with simple continue or base might simply stay at DYNAMIC_BASE.
>
> I will send a v2 of this patch with refined logic.

Actually it would be nice to integrate a warning (if we don't have it
yet) when adding a GPIO chip with a static allocation and which will
overlap the dynamic base. Can you add that into your v2?


-- 
With Best Regards,
Andy Shevchenko