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References: <f31b818cf8d682de61c74b133beffcc8a8202478.1660041358.git.christophe.leroy@csgroup.eu>
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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 18 Aug 2022 11:47:55 +0200
Message-ID: <CAK8P3a1Vh1Uehuin-u5QrTO5qh+t0aK_hA-QZwqc00Db_+MKcw@mail.gmail.com>
Subject: Re: [PATCH] gpio: Allow user to customise maximum number of GPIOs
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Jonathan Corbet <corbet@lwn.net>,
        Russell King <linux@armlinux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@vger.kernel.org>
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On Thu, Aug 18, 2022 at 11:33 AM Linus Walleij <linus.walleij@linaro.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