linux-kernel - Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs

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Message-ID: <CAK8P3a1Vh1Uehuin-u5QrTO5qh+t0aK_hA-QZwqc00Db_+MKcw@mail.gmail.com>
Date:   Thu, 18 Aug 2022 11:47:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Jonathan Corbet <corbet@....net>,
        Russell King <linux@...linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs

On Thu, Aug 18, 2022 at 11:33 AM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> The per-arch GPIO number only exist for one reason: embedded
> GPIOs (think SoC:s) that refer to fixed numbers in numberspace in
> the board support code. This makes it necessary to allocate
> descriptors up front in some compiled-in GPIO chips.

As I understood, the problem that Christophe ran into is that the
dynamic registration of additional gpio chips is broken because
it unregisters the chip if the number space is exhausted:

                base = gpiochip_find_base(gc->ngpio);
                if (base < 0) {
                        ret = base;
                        spin_unlock_irqrestore(&gpio_lock, flags);
                        goto err_free_label;
                }

>From the git history, it looks like this error was never handled gracefully
even if the intention was to keep going without a number assignment,
so there are probably other bugs one runs into after changing this.

        Arnd