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

[Guenter Roeck]

On 3/19/22 02:28, Geert Uytterhoeven wrote:
> Hi Alistair,
>
> On Sat, Mar 19, 2022 at 3:36 AM Alistair Francis <alistair23@xxxxxxxxx> wrote:
> > On Tue, Mar 8, 2022 at 8:53 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > > Acked-for-MFD-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > >
> > > > --- 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.

Guenter

> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds