RE: [PATCH v2 2/4] mfd: Add RZ/V2M PWC core driver

[Fabrizio Castro]

Hi Geert,

Thank you for your feedback!

> From: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Sent: 03 January 2023 12:10
> Subject: Re: [PATCH v2 2/4] mfd: Add RZ/V2M PWC core driver
> 
> Hi Fabrizio,
> 
> On Tue, Jan 3, 2023 at 1:05 PM Fabrizio Castro
> <fabrizio.castro.jz@xxxxxxxxxxx> wrote:
> > > From: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > > On Wed, Dec 21, 2022 at 10:09 PM Fabrizio Castro
> > > <fabrizio.castro.jz@xxxxxxxxxxx> wrote:
> > > > The External Power Sequence Controller (PWC) IP (found in the
> > > > RZ/V2M SoC) is a controller for external power supplies (regulators
> > > > and power switches), and it supports the following features: it
> > > > generates a power on/off sequence for external power supplies,
> > > > it generates an on/off sequence for the LPDDR4 core power supply
> > > > (LPVDD), it comes with General-Purpose Outputs, and it processes
> > > > key input signals.
> > >
> > > Thanks for your patch!
> > >
> > > > The PWC is basically a Multi-Function Device (MFD), its software
> > > > support comes with a core driver, and specialized drivers for
> > > > its specific features.
> > >
> > > I have to admit I'm not such a big fan of MFD.  In this driver,
> > > you are not even sharing resources in the MFD cells, just the mapped
> > > register base.  So I think you can easily save +100 LoC and reduce
> > > maintenance synchronization overhead across subsystems by just having
> > > a single non-MFD driver instead.
> > >
> > > Did you pick MFD because the PWC poweroff feature depends on board
> > > wiring, and thus is optional?
> >
> > I am not a big fan of MFD, either.
> > I picked MFD because we were not 100% sure of what the IP could do
> > when we started working on it.
> > I have received more information regarding the IP now (which I don't
> > have the liberty to discuss), I am still not 100% sure that's all
> > of it, but basically its support may require expansion later on.
> >
> > I liked the solution based on syscon and simple-mfd for several reasons,
> > but having dropped syscon and simple-mfd due to issues with the dt-
> bindings
> > I have moved on with a core driver to instantiate the required SW
> support.
> > We could of course move to a unified driver if that makes more sense?
> > If we were to move to unified driver, under which directory would you
> > suggest we put it?
> 
> As the GPIO part is larger than the poweroff part, I would put it under
> drivers/gpio/.  Although drivers/soc/renesas/ could be an option, too.

I'll try the unified approach then, under drivers/soc/renesas .

Thanks,
Fab 

> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> 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