linux-kernel - Re: [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller

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Date:   Mon, 10 Aug 2020 09:31:38 +0200
From:   Michael Walle <michael@...le.cc>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Thierry Reding <thierry.reding@...il.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v7 06/13] pwm: add support for sl28cpld PWM controller

Am 2020-08-10 09:13, schrieb Lee Jones:
> On Fri, 07 Aug 2020, Michael Walle wrote:
> 
>> Hi Uwe, Hi Lee,
>> 
>> Am 2020-08-06 10:40, schrieb Uwe Kleine-König:
>> > On Mon, Aug 03, 2020 at 11:35:52AM +0200, Michael Walle wrote:
>> > > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> > > index 7dbcf6973d33..a0d50d70c3b9 100644
>> > > --- a/drivers/pwm/Kconfig
>> > > +++ b/drivers/pwm/Kconfig
>> > > @@ -428,6 +428,16 @@ config PWM_SIFIVE
>> > >  	  To compile this driver as a module, choose M here: the module
>> > >  	  will be called pwm-sifive.
>> > >
>> > > +config PWM_SL28CPLD
>> > > +	tristate "Kontron sl28cpld PWM support"
>> > > +	select MFD_SIMPLE_MFD_I2C
>> >
>> > Is it sensible to present this option to everyone? Maybe
>> >
>> > 	depends on SOME_SYMBOL_ONLY_TRUE_ON_SL28CPLD || COMPILE_TEST
>> 
>> Because there is now no real MFD driver anymore, there is also
>> no symbol for that. The closest would be ARCH_ARM64 but I don't
>> think that is a good idea.
>> 
>> Lee, what do you think about adding a symbol to the MFD, which
>> selects MFD_SIMPLE_MFD_I2C but doesn't enable any C modules?
>> 
>> I.e.
>> config MFD_SL28CPLD
>>     tristate "Kontron sl28cpld"
>>     select MFD_SIMPLE_MFD_I2C
>>     help
>>       Say yes here to add support for the Kontron sl28cpld board
>>       management controller.
>> 
>> Then all the other device driver could depend on the MFD_SL28CPLD
>> symbol.
> 
> You want to add a virtual symbol to prevent having to present a real
> one?  How is that a reasonable solution?

(1) Its a symbol on which all sl28cpld will depend on. Thus they will
     all be hidden if that is not set.
(2) the drivers itself wouldn't need to depend on MFD_SIMPLE_MFD_I2C,
     which is more correct, because they don't have anything to do with
     i2c.

-michael