linux-kernel - Re: [PATCH 2/2] i2c: rcar: add FastMode+ support for Gen4

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Date:   Tue, 19 Sep 2023 11:51:59 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     linux-renesas-soc@...r.kernel.org,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Andi Shyti <andi.shyti@...nel.org>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] i2c: rcar: add FastMode+ support for Gen4

Hi Wolfram,

On Thu, Sep 14, 2023 at 1:16 AM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
> To support FM+, we mainly need to turn the SMD constant into a parameter
> and set it accordingly. Then, activating the enable bit for FM+ is all
> we need to do. Tested with a Renesas Falcon board using R-Car V3U.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

Thanks for your patch!

> --- a/drivers/i2c/busses/i2c-rcar.c
> +++ b/drivers/i2c/busses/i2c-rcar.c
> @@ -297,11 +307,18 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
>          * clkp : peripheral_clk
>          * F[]  : integer up-valuation
>          */
> -       rate = clk_get_rate(priv->clk);
> -       cdf = rate / 20000000;
> -       cdf_width = (priv->devtype == I2C_RCAR_GEN1) ? 2 : 3;
> -       if (cdf >= 1U << cdf_width)
> -               goto err_no_val;
> +       if (t.bus_freq_hz > I2C_MAX_FAST_MODE_FREQ && priv->devtype >= I2C_RCAR_GEN4) {
> +               priv->flags |= ID_P_FMPLUS;
> +               /* FM+ needs lower SMD and no filters */
> +               priv->smd /= 2;
> +               cdf = 0;

Is this documented somewhere in the R-Car Gen4 docs?
Assumed this is true, the rest LGTM, modulo the few fixes that should be
moved to "[PATCH RFT 2/2] i2c: rcar: improve accuracy for R-Car Gen3+".

> +       } else {
> +               priv->flags &= ~ID_P_FMPLUS;
> +               cdf = rate / 20000000;
> +               cdf_width = (priv->devtype == I2C_RCAR_GEN1) ? 2 : 3;
> +               if (cdf >= 1U << cdf_width)
> +                       goto err_no_val;
> +       }
>

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