linux-kernel - Re: [PATCH v2 2/4] mfd: Add RZ/V2M PWC core driver

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Date:   Tue, 3 Jan 2023 13:10:25 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Fabrizio Castro <fabrizio.castro.jz@...esas.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sebastian Reichel <sre@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Lee Jones <lee@...nel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jacopo Mondi <jacopo@...ndi.org>
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@...esas.com> wrote:
> > From: Geert Uytterhoeven <geert@...ux-m68k.org>
> > On Wed, Dec 21, 2022 at 10:09 PM Fabrizio Castro
> > <fabrizio.castro.jz@...esas.com> 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.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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