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In-Reply-To: <abb46a587b76d379ad32d53817d837d8a5fea8bd.1661789204.git.christophe.leroy@csgroup.eu>
From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Tue, 30 Aug 2022 23:18:26 +0300
Message-ID: <CAHp75VcngRihpfUkeKs-g+TbPnpOsZ+-Q37zDVoWp8p_2GbSvQ@mail.gmail.com>
Subject: Re: [PATCH v1 4/8] gpiolib: Get rid of ARCH_NR_GPIOS
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Keerthy <j-keerthy@ti.com>, Russell King <linux@armlinux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Jonathan Corbet <corbet@lwn.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        Linux-Arch <linux-arch@vger.kernel.org>,
        Linux Documentation List <linux-doc@vger.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>
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On Mon, Aug 29, 2022 at 7:19 PM Christophe Leroy
<christophe.leroy@csgroup.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