linux-kernel - Re: [RFC PATCH 4/4] pinctrl: renesas: pinctrl-rzg2l: Add support to get/set drive-strength and output-impedance

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Message-ID: <CA+V-a8uS6fiHAWbJTXtVJgHPqvtDGPf-RupQGaKJv7wWkurLYw@mail.gmail.com>
Date:   Tue, 26 Oct 2021 22:36:17 +0100
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [RFC PATCH 4/4] pinctrl: renesas: pinctrl-rzg2l: Add support to
 get/set drive-strength and output-impedance

Hi Geert,

Thank you for the review.

On Thu, Oct 7, 2021 at 6:23 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Thu, Sep 30, 2021 at 2:17 PM Lad Prabhakar
> <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> > Add support to get/set drive-strength and output-impedance of the pins.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> Thanks for your patch!
>
> > --- a/drivers/pinctrl/renesas/pinctrl-rzg2l.c
> > +++ b/drivers/pinctrl/renesas/pinctrl-rzg2l.c
> > @@ -47,6 +47,7 @@
> >  #define PIN_CFG_FILONOFF               BIT(9)
> >  #define PIN_CFG_FILNUM                 BIT(10)
> >  #define PIN_CFG_FILCLKSEL              BIT(11)
> > +#define PIN_CFG_GROUP_B                        BIT(12)
>
> Perhaps it would be easier to have separate PIN_CFG_IOLH_A and
> PIN_CFG_IOLH_B flags, instead of a PIN_CFG_IOLH flag and a
> PIN_CFG_GROUP_B modifier flag?
>
Agreed will do that.

> >
> >  #define RZG2L_MPXED_PIN_FUNCS          (PIN_CFG_IOLH | \
> >                                          PIN_CFG_SR | \
>
> > @@ -484,6 +513,38 @@ static int rzg2l_pinctrl_pinconf_get(struct pinctrl_dev *pctldev,
> >                 break;
> >         }
> >
> > +       case PIN_CONFIG_OUTPUT_IMPEDANCE:
> > +       case PIN_CONFIG_DRIVE_STRENGTH: {
> > +               unsigned int mA[4] = { 2, 4, 8, 12 };
> > +               unsigned int oi[4] = { 100, 66, 50, 33 };
>
> static const
>
agreed.

> > +
> > +               if (param == PIN_CONFIG_DRIVE_STRENGTH) {
> > +                       if (!(cfg & PIN_CFG_IOLH) || groupb_pin)
> > +                               return -EINVAL;
> > +               } else {
> > +                       if (!(cfg & PIN_CFG_IOLH) || !groupb_pin)
> > +                               return -EINVAL;
> > +               }
> > +
> > +               spin_lock_irqsave(&pctrl->lock, flags);
> > +
> > +               /* handle _L/_H for 32-bit register read/write */
> > +               addr = pctrl->base + IOLH(port);
> > +               if (bit >= 4) {
> > +                       bit -= 4;
> > +                       addr += 4;
> > +               }
> > +
> > +               reg = readl(addr) & (IOLH_MASK << (bit * 8));
> > +               reg = reg >> (bit * 8);
> > +               if (param == PIN_CONFIG_DRIVE_STRENGTH)
> > +                       arg = mA[reg];
> > +               else
> > +                       arg = oi[reg];
> > +               spin_unlock_irqrestore(&pctrl->lock, flags);
>
> I think you've reached the point where it starts to make sense to
> have helper functions to read and modify these sub-register fields
> that may be located into the current or next register.
>
Ok will add helpers to read and rmw.

> And after that, you can split it in two smaller separate cases for
> drive strength and output impedance.
>
Agreed.

Cheers,
Prabhakar

> > +               break;
> > +       }
> > +
> >         default:
> >                 return -ENOTSUPP;
> >         }
>
> 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