linux-kernel - Re: [PATCH v2] mux: remove the Kconfig question for the subsystem

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Date:   Wed, 7 Dec 2022 11:15:07 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>, Peter Rosin <peda@...ntia.se>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mux: remove the Kconfig question for the subsystem



On 12/7/22 11:03, Randy Dunlap wrote:
> 
> 
> On 12/7/22 10:57, Arnd Bergmann wrote:
>> On Wed, Dec 7, 2022, at 18:19, Randy Dunlap wrote:
>>> On 12/7/22 00:41, Arnd Bergmann wrote:
>>>> For the other subsystems I mentioned, there are occasionally 
>>>> problems with missing 'select' that tend to be a pain to find,
>>>> compared to subsystems consistently using 'depends on', which
>>>> show up as link failures in randconfig builds.
>>>
>>> I find that various drivers mixing the use of "select" and
>>> "depends on" is problematic.
>>
>> Agreed. Even just mixing 'select' with user-visible symbols
>> is very confusing. The two sensible ways are either using
>> user-visible options with 'depends on' or hidden options with
>> 'select'.
>>
>>> However, there was no answer for the original question:
>>> How does a user enable the 4 Kconfig symbols in drivers/mux/Kconfig
>>> if some other random driver has not selected MULTIPLEXER?
>>
>> There is no need to enable any of them in this case, because
>> the mux drivers are not usable by themselves.
>>
>>> I.e.:
>>>
>>> config MUX_ADG792A
>>> 	tristate "Analog Devices ADG792A/ADG792G Multiplexers"
>>>
>>> config MUX_ADGS1408
>>> 	tristate "Analog Devices ADGS1408/ADGS1409 Multiplexers"
>>>
>>> config MUX_GPIO
>>> 	tristate "GPIO-controlled Multiplexer"
>>>
>>> config MUX_MMIO
>>> 	tristate "MMIO/Regmap register bitfield-controlled Multiplexer"
>>>
>>> OK, MUX_MMIO is selected from some other drivers, but if that is not done,
>>> how can the first 3 be enabled by a user?
>>
>> They cannot, that is the entire point of hiding the subsystem
>> when it is not used.
> 
> OK, if you say so. That doesn't make any sense to me, but whatever,
> I'll drop it.

Oops. One more thing:
Your statement leads me to conclude that since nothing selects those 3 mux drivers,
they don't need to be in the kernel tree at all.

Done. (I hope.)

-- 
~Randy