linux-kernel - Re: [PATCH v1 12/16] pinctrl: starfive: Add pinctrl driver for StarFive SoCs

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Date:   Wed, 13 Oct 2021 19:50:02 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Emil Renner Berthing <kernel@...il.dk>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Drew Fustini <drew@...gleboard.org>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Matteo Croce <mcroce@...rosoft.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Huan Feng <huan.feng@...rfivetech.com>
Subject: Re: [PATCH v1 12/16] pinctrl: starfive: Add pinctrl driver for
 StarFive SoCs

On Wed, Oct 13, 2021 at 6:58 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Wed, Oct 13, 2021 at 06:38:14PM +0200, Emil Renner Berthing wrote:
> > On Tue, 12 Oct 2021 at 19:03, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > > On Tue, Oct 12, 2021 at 4:43 PM Emil Renner Berthing <kernel@...il.dk> wrote:

> > > > +               v = pinmux[i];
> > > > +               dout = ((v & BIT(7)) << (31 - 7)) | ((v >> 24) & 0xffU);
> > > > +               doen = ((v & BIT(6)) << (31 - 6)) | ((v >> 16) & 0xffU);
> > > > +               din  = (v >> 8) & 0xffU;
> > >
> > > What is this voodoo for?
> >
> > In order to do pinmux we need the following pieces of information from
> > the device tree for each pin ("GPIO" they call it):
> >
> > output signal: 0-133 + 1bit reverse flag
> > output enable signal: 0-133 + 1bit reverse flag
> > optional input signal: 0-74 + special "none" value, right now 0xff
> > gpio number: 0-63
> >
> > As the code is now all that info is packed into a u32 for each pin
> > using the GPIOMUX macro defined in the dt-binding header added in
> > patch 10. There is also a diagram for how this packing is done. The
> > above voodoo is for unpacking that.
> >
> > I'd very much like to hear if you have a better solution for how to
> > convey that information from the device tree to here.
>
> At very least this code should have something like above in the comment.

And perhaps introduce some helper macros to access the fields?

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