Hi Wolfram,
On Wed, Sep 6, 2023 at 2:11 PM Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > ick = rate / (cdf + 1);
> >
> > In case of FM+, cdf will be zero, and ick == rate?
>
> Yes.
>
> > > @@ -292,34 +324,55 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv)
> > > round = (ick + 500000) / 1000000 * sum;
> >
> > ick == rate if FM+
>
> Yes, does this induce a change here?
No, just pointing it out, and wondering if this is intended...
>
> > > round = (round + 500) / 1000;
> >
> > DIV_ROUND_UP()
>
> DIV_ROUND_CLOSEST() I'd say, but I have a seperate patch for that.
Oops (it's too hot here for more coffee...)
> > > + if (priv->flags & ID_P_FMPLUS) {
> >
> > IIUIC, on R-ar Gen3 and later you can use ICCCR2 without FM+, for
> > improved accuracy, too?
>
> Yeah, we could do that. It indeed improves accuracy:
>
> old new
> 100kHz: 97680/100000 99950/100000
> 400kHz: 373482/400000 399201/400000
>
> Caring about regressions here is a bit over the top, or?
Probably OK.
> > > + /*
> > > + * SMD should be smaller than SCLD and SCHD, we arbitrarily set
> > > + * the ratio 1:3. SCHD:SCLD ratio is 1:1, thus:
> > > + * SCL = clkp / (8 + SMD * 2 + SCLD + SCHD + F[(ticf + tr + intd) * clkp])
> > > + * SCL = clkp / (8 + SMD * 2 + SMD * 3 + SMD * 3 + F[...])
> > > + * SCL = clkp / (8 + SMD * 8 + F[...])
> > > + */
> > > + smd = DIV_ROUND_UP(ick / t.bus_freq_hz - 8 - round, 8);
> >
> > Perhaps use rate instead of ick?
>
> That's probably cleaner.
>
> > DIV_ROUND_UP(ick, 8 * (t.bus_freq_hz - 8 - round));
>
> This looks like you assumed "ick / (t.bus_freq_hz - 8 - round)" but it
> is "(ick / t.bus_freq_hz) - 8 - round"?
Oops (again)
OK do you need rounding for the division of ick and t.bus_freq_hz,
or is the adjustment bij "- (round + 8)" already taking care of that?
I guess I just don't understand the intended formula here...
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
