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

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Date:   Tue, 3 Jan 2023 12:05:06 +0000
From:   Fabrizio Castro <fabrizio.castro.jz@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
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 Geert,

Thanks for your feedback!

> -----Original Message-----
> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: 03 January 2023 08:37
> 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; devicetree@...r.kernel.org; linux-
> kernel@...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; 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 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?

> 
> Are there any other MFD cells planned (e.g. regulators) to be added
> later? The public datasheet does not list the actual registers of the
> block, only a high-level overview with (rather detailed) behavioral
> information.

No MFD cells are planned for now, but I can't exclude we won't
have any in the future.

Thanks,
Fab

> 
> Thanks!
> 
> > --- /dev/null
> > +++ b/drivers/mfd/rzv2m-pwc.h
> 
> > +struct rzv2m_pwc_priv {
> > +       void __iomem *base;
> > +};
> > +
> > +#endif /* __LINUX_RZV2M_PWC_H__ */
> 
> 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