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

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Date:   Thu, 27 Apr 2023 09:00:47 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Andreas Kemnade <andreas@...nade.info>,
        "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 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.

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.


-- 
With Best Regards,
Andy Shevchenko