linux-kernel - Re: [PATCH v1 1/5] gpiolib: fix linker errors when GPIOLIB is disabled

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Message-Id: <05d32a58-c119-4abb-8e62-9d79bd95324f@app.fastmail.com>
Date:   Thu, 26 Jan 2023 09:40:18 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Christophe Leroy" <christophe.leroy@...roup.eu>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        "Bartosz Golaszewski" <bartosz.golaszewski@...aro.org>,
        "Dmitry Torokhov" <dmitry.torokhov@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "Linus Walleij" <linus.walleij@...aro.org>,
        "Bartosz Golaszewski" <brgl@...ev.pl>,
        "Pierluigi Passaro" <pierluigi.p@...iscite.com>,
        "kernel test robot" <lkp@...el.com>
Subject: Re: [PATCH v1 1/5] gpiolib: fix linker errors when GPIOLIB is disabled

On Thu, Jan 26, 2023, at 09:14, Christophe Leroy wrote:
> Le 25/01/2023 à 21:10, Andy Shevchenko a écrit :
>> From: Pierluigi Passaro <pierluigi.p@...iscite.com>
>> 
>> Both the functions gpiochip_request_own_desc and
>> gpiochip_free_own_desc are exported from
>>      drivers/gpio/gpiolib.c
>> but this file is compiled only when CONFIG_GPIOLIB is enabled.
>> Move the prototypes under "#ifdef CONFIG_GPIOLIB" and provide
>> reasonable definitions and includes in the "#else" branch.
>
> Can you give more details on when and why link fails ?
>
> You are adding a WARN(), I understand it mean the function should never 
> ever be called. Shouldn't it be dropped completely by the compiler ? In 
> that case, no call to gpiochip_request_own_desc() should be emitted and 
> so link should be ok.
>
> If link fails, it means we still have unexpected calls to 
> gpiochip_request_own_desc() or gpiochip_free_own_desc(), and we should 
> fix the root cause instead of hiding it with a WARN().

There are only a handful of files calling these functions:

$ git grep -l gpiochip_request_own_desc
Documentation/driver-api/gpio/driver.rst
arch/arm/mach-omap1/ams-delta-fiq.c
arch/arm/mach-omap1/board-ams-delta.c
drivers/gpio/gpio-mvebu.c
drivers/gpio/gpiolib-acpi.c
drivers/gpio/gpiolib.c
drivers/hid/hid-cp2112.c
drivers/memory/omap-gpmc.c
drivers/net/wireless/broadcom/brcm80211/brcmsmac/led.c
drivers/power/supply/collie_battery.c
drivers/spi/spi-bcm2835.c
include/linux/gpio/driver.h

All of these should already prevent the link failure through
a Kconfig 'depends on GPIOLIB' for the driver, or 'select GPIOLIB'
for the platform code. I checked all of the above and they seem fine.
If anything else calls the function, I'd add the same dependency
there.

      Arnd