linux-kernel - Re: [PATCH 3/3] i2c: rcar: add FastMode+ support

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Message-ID: <CAMuHMdV3Ka9fh6fmyYj7j5xdm3LEYsMjgXDk90be3AC7gDFozA@mail.gmail.com>
Date:   Thu, 7 Sep 2023 09:09:18 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Andi Shyti <andi.shyti@...nel.org>,
        linux-renesas-soc@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] i2c: rcar: add FastMode+ support

Hi Wolfram,

On Thu, Sep 7, 2023 at 7:39 AM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
> > > @@ -217,7 +228,17 @@ static void rcar_i2c_init(struct rcar_i2c_priv *priv)
> > >     rcar_i2c_write(priv, ICMCR, MDBS);
> > >     rcar_i2c_write(priv, ICMSR, 0);
> > >     /* start clock */
> > > -   rcar_i2c_write(priv, ICCCR, priv->icccr);
> > > +   if (priv->flags & ID_P_FMPLUS) {
> > > +           rcar_i2c_write(priv, ICCCR, 0);
> > > +           rcar_i2c_write(priv, ICMPR, priv->clock_val);
> > > +           rcar_i2c_write(priv, ICHPR, 3 * priv->clock_val);
> > > +           rcar_i2c_write(priv, ICLPR, 3 * priv->clock_val);
> > > +           rcar_i2c_write(priv, ICCCR2, FMPE | CDFD | HLSE | SME);
> > > +   } else {
> > > +           rcar_i2c_write(priv, ICCCR, priv->clock_val);
> > > +           if (priv->devtype >= I2C_RCAR_GEN3)
> > > +                   rcar_i2c_write(priv, ICCCR2, 0);
> >
> > is this last bit part of the FM+ enabling or is it part of the
> > GEN4 support?
>
> It is "disabling FM+" for lower speeds. Since we never used ICCCR2
> before FM+, we need to make sure it is cleared properly.

This may become clearer if you first introduce support for ICCCR2
on R-Car Gen3 and later, to improve i2c rate accuracy, and add
support for FM+ in a separate patch?

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