On Tue, Sep 19, 2023 at 11:42 AM Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
> On Wed, Sep 13, 2023 at 11:38 AM Wolfram Sang
> <wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
> > With some new registers, SCL can be calculated to be closer to the
> > desired rate. Apply the new formula for R-Car Gen3 device types.
> >
> > Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
>
> > --- a/drivers/i2c/busses/i2c-rcar.c
> > +++ b/drivers/i2c/busses/i2c-rcar.c
>
> > - /* keep icccr value */
> > - priv->icccr = scgd << cdf_width | cdf;
> > + priv->icccr = scgd << cdf_width | cdf;
> > + } else {
> > + u32 x, sum_ratio = RCAR_SCHD_RATIO + RCAR_SCLD_RATIO;
> > + /*
> > + * SCLD/SCHD ratio and SMD default value are explained above
> > + * where they are defined. With these definitions, we can compute
> > + * x as a base value for the SCLD/SCHD ratio:
> > + *
> > + * SCL = clkp / (8 + 2 * SMD + SCLD + SCHD + F[(ticf + tr + intd) * clkp])
> > + * SCL = clkp / (8 + 2 * RCAR_DEFAULT_SMD + RCAR_SCLD_RATIO * x
> > + * + RCAR_SCHD_RATIO * x + F[...])
> > + *
> > + * with: sum_ratio = RCAR_SCLD_RATIO + RCAR_SCHD_RATIO
> > + * and: smd = 2 * RCAR_DEFAULT_SMD
> > + *
> > + * SCL = clkp / (8 + smd + sum_ratio * x + F[...])
> > + * 8 + smd + sum_ratio * x + F[...] = SCL / clkp
> > + * x = ((SCL / clkp) - 8 - smd - F[...]) / sum_ratio
>
> Woops, I missed that both "SCL / clkp" above should be "clkp / SCL".
>
> Fortunately I noticed your "[PATCH 2/2] i2c: rcar: add FastMode+
> support for Gen4" fixed that, but I guess it's better to fix that in
> this patch instead.
And while at it, please move the "2 *" to replace "smd" by "2 * smd", to
match the docs, and the result after FM+?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
