linux-kernel - Re: [PATCH v1 4/8] gpiolib: Get rid of ARCH_NR

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Date:   Tue, 30 Aug 2022 23:18:26 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Keerthy <j-keerthy@...com>, Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux Documentation List <linux-doc@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH v1 4/8] gpiolib: Get rid of ARCH_NR_GPIOS

On Mon, Aug 29, 2022 at 7:19 PM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
> Since commit 14e85c0e69d5 ("gpio: remove gpio_descs global array")
> there is no limitation on the number of GPIOs that can be allocated
> in the system since the allocation is fully dynamic.
>
> ARCH_NR_GPIOS is today only used in order to provide downwards
> gpiobase allocation from that value, while static allocation is
> performed upwards from 0. However that has the disadvantage of
> limiting the number of GPIOs that can be registered in the system.
>
> To overcome this limitation without requiring each and every
> platform to provide its 'best-guess' maximum number, rework the
> allocation to allocate upwards, allowing approx 2 millions of
> GPIOs.
>
> In order to still allow static allocation for legacy drivers, define
> GPIO_DYNAMIC_BASE with the value 256 as the start for dynamic
> allocation.

Not sure about 256, but I understand that this can only be the best guess.

-- 
With Best Regards,
Andy Shevchenko