linux-kernel - Re: [PATCH v18 2/8] mfd: simple-mfd-i2c: Add a Kconfig name

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Date:   Mon, 21 Mar 2022 08:48:13 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Alistair Francis <alistair23@...il.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Alistair Francis <alistair@...stair23.me>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Liam Girdwood <lgirdwood@...il.com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        linux-hwmon@...r.kernel.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, NXP Linux Team <linux-imx@....com>,
        Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amitk@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Andreas Kemnade <andreas@...nade.info>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>
Subject: Re: [PATCH v18 2/8] mfd: simple-mfd-i2c: Add a Kconfig name

On Mon, 21 Mar 2022, Alistair Francis wrote:

> On Sun, Mar 20, 2022 at 12:48 AM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > On 3/19/22 02:28, Geert Uytterhoeven wrote:
> > > Hi Alistair,
> > >
> > > On Sat, Mar 19, 2022 at 3:36 AM Alistair Francis <alistair23@...il.com> wrote:
> > >> On Tue, Mar 8, 2022 at 8:53 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > >>> Thanks for your patch, which is now commit bae5a4acef67db88
> > >>> ("mfd: simple-mfd-i2c: Add a Kconfig name") in mfd/for-mfd-next.
> > >>>
> > >>> On Mon, Jan 24, 2022 at 1:24 PM Alistair Francis <alistair@...stair23.me> wrote:
> > >>>> Add a Kconfig name to the "Simple Multi-Functional Device support (I2C)"
> > >>>> device so that it can be enabled via menuconfig.
> > >>>
> > >>> Which still does not explain why this would be needed...
> > >>>
> > >>>> Signed-off-by: Alistair Francis <alistair@...stair23.me>
> > >>>> Acked-for-MFD-by: Lee Jones <lee.jones@...aro.org>
> > >>>
> > >>>> --- a/drivers/mfd/Kconfig
> > >>>> +++ b/drivers/mfd/Kconfig
> > >>>> @@ -1188,7 +1188,7 @@ config MFD_SI476X_CORE
> > >>>>            module will be called si476x-core.
> > >>>>
> > >>>>   config MFD_SIMPLE_MFD_I2C
> > >>>> -       tristate
> > >>>> +       tristate "Simple Multi-Functional Device support (I2C)"
> > >>>>          depends on I2C
> > >>>>          select MFD_CORE
> > >>>>          select REGMAP_I2C
> > >>>
> > >>> The help text states:
> > >>>
> > >>> | This driver creates a single register map with the intention for it
> > >>> | to be shared by all sub-devices.
> > >>>
> > >>> Yes, that's what MFD does?
> > >>>
> > >>> | Once the register map has been successfully initialised, any
> > >>> | sub-devices represented by child nodes in Device Tree will be
> > >>> | subsequently registered.
> > >>>
> > >>> OK...?
> > >>>
> > >>> Still, no clue about what this driver really does, and why and when
> > >>> it would be needed.
> > >>>
> > >>> There is one driver symbol that selects MFD_SIMPLE_MFD_I2C.
> > >>> There are no driver symbols that depend on this symbol.
> > >>>
> > >>> If you have a driver in the pipeline that can make use of this,
> > >>> can't it just select MFD_SIMPLE_MFD_I2C, so the symbol itself can
> > >>> stay invisible?
> > >>
> > >> My patch "mfd: simple-mfd-i2c: Enable support for the silergy,sy7636a"
> > >> allows using this driver for the silergy,sy7636a MFD. So it's nice to
> > >> be able to enable and disable it as required.
> > >
> > > So after that patch, enabling MFD_SIMPLE_MFD_I2C will enable
> > > support for an ever-growing random bunch of devices, none of which
> > > is described in the help text?
> > > To me, ghat doesn't look like the way to go forward...
> > >
> >
> > I am probably missing something. Why not something like the following ?
> >
> > config MFD_SY7636A
> >          tristate "Silergy SY7636A voltage regulator"
> >          depends on I2C
> >          select MFD_SIMPLE_MFD_I2C
> >          help
> >            Enable support for Silergy SY7636A voltage regulator.
> >
> >            To enable support for building sub-devices as modules,
> >            choose M here.
> >
> >
> > This would be quite similar to MFD_SL28CPLD which essentially does
> > the same (and, unless I am missing something, doesn't have its own
> > driver either). Sub-devices would then depend on MFD_SY7636A.
> 
> That's fine with me.
> 
> As you said this patch is already in the mfd/for-mfd-next tree, should
> I resend the series?

Making the symbol selectable-only is fine with me also.

Please send a subsequent patch.

-- 
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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