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

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Date:   Wed, 7 Dec 2022 11:03:12 -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 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.

Thanks.

-- 
~Randy