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

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Message-ID: <7b7df1f7-4f47-d19a-02ff-91984b25ba98@csgroup.eu>
Date:   Thu, 26 Jan 2023 12:44:01 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Arnd Bergmann <arnd@...db.de>,
        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



Le 26/01/2023 à 11:19, Andy Shevchenko a écrit :
> On Thu, Jan 26, 2023 at 08:14:49AM +0000, 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().
> 
> I agree, but what do you suggest exactly? I think the calls to that functions
> shouldn't be in the some drivers as it's layering violation (they are not a
> GPIO chips to begin with). Simply adding a dependency not better than this one.
> 

My suggestion is to go step by step. First step is to explicitely list 
drivers that call those functions without selecting GPIOLIB.

Once we have this list we can see one by one how we solve it.

And if we want to catch the problem before the final link, then I think 
we may use BUILD_BUG() but not WARN or WARN_ON.

Christophe