linux-kernel - Re: [RFC PATCH] drivers: use 'depends on MFD_SYSCON' instead of 'select MFD

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Date:   Tue, 27 Feb 2018 09:46:53 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH] drivers: use 'depends on MFD_SYSCON' instead of
 'select MFD_SYSCON'

2018-02-26 21:43 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> On Mon, Feb 26, 2018 at 12:53 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> 2018-02-26 17:43 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
>>> On Sat, Feb 24, 2018 at 3:50 PM, Masahiro Yamada
>>> <yamada.masahiro@...ionext.com> wrote:
>>>> As Documentation/kbuild/kconfig-language.txt notes, 'select' should be
>>>> used with care - it forces a lower limit of another symbol, ignoring
>>>> the dependency.
>>>>
>>>> MFD_SYSCON depends on HAS_IOMEM, but several drivers with COMPILE_TEST
>>>> select it.
>>>>
>>>> This causes unmet dependencies for architecture without HAS_IOMEM.
>>>>
>>>>   $ make ARCH=score randconfig
>>>>   scripts/kconfig/conf  --randconfig Kconfig
>>>>   KCONFIG_SEED=0x27C47F43
>>>>   warning: (HWSPINLOCK_QCOM && AHCI_MTK && STMMAC_PLATFORM && ...)
>>>>   selects MFD_SYSCON which has unmet direct dependencies (HAS_IOMEM)
>>>>
>>>> Use 'depends on' to observe the dependency.
>>>>
>>>> This commit was created by the following command:
>>>>
>>>>   $ find drivers -name 'Kconfig*' | xargs sed -i -e \
>>>>     's/select MFD_SYSCON$/depends on MFD_SYSCON/'
>>>>
>>>> Then, COMMON_CLK_NXP and S3C2410_WATCHDOG were fixed up manually.
>>>>
>>>> Also, make MFD_SYSCON 'default y' because some defconfig files may
>>>> rely on someone select's MFD_SYSCON.
>>>>
>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>>>> ---
>>>>
>>>> If you have a better idea to fix 'unmet dependencies',
>>>> please suggest.
>>>
>>> Changing 'select MFD_SYSCON' to 'depends on' will definitely break lots
>>> of defconfig configurations, I'd rather not do that.
>>
>>
>> Could you explain why?
>>
>> I set 'default y' for MFD_SYSCON.
>>
>> Would it still break defconfig configurations?
>
> No, you are right, that would not break defconfigs, it would just mean one
> useless driver being enabled for many configurations that don't need it.

If we are unhappy about this,
we can send per-arch patches
to add CONFIG_MTD_SYSCON=y to defconfigs that need it.

But, we need to decide what the right solution is.


>>> Only score, tile and um have some configurations that select 'NO_IOMEM'.
>>> Score is getting removed now, tile might get removed later (we could make
>>> PCI mandatory in the meantime to avoid that configuration), and I think for
>>> um, we already have a workaround for the NO_IOMEM dependencies
>>> (I forget the details).
>>
>> I do not think this is a stable solution.
>>
>> Or, do you mean to remove NO_IOMEM and HAS_IOMEM completely?
>
> We could either leave it for arch/um only and have that deal with the
> issues (which I think we already have), or we could remove the options
> entirely.
>
>       Arnd
> --
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-- 
Best Regards
Masahiro Yamada