Re: [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm

[Nylon Chen <nylon.chen@sifive.com>]

Hi Geert,

Thanks for your reply.

Geert Uytterhoeven <geert@linux-m68k.org> 於 2023年1月30日 週一 下午5:53寫道：
>
> Hi Nylon,
>
> On Mon, Jan 30, 2023 at 10:32 AM Nylon Chen <nylon.chen@sifive.com> wrote:
> > The `frac` variable represents the pulse inactive time, and the result of
> > this algorithm is the pulse active time. Therefore, we must reverse the
> > result.
> >
> > The reference is SiFive FU740-C000 Manual[0].
> >
> > [0]: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
> >
> > Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
>
> Thanks for your patch!
>
> > --- a/drivers/pwm/pwm-sifive.c
> > +++ b/drivers/pwm/pwm-sifive.c
> > @@ -158,6 +158,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >         frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
> >         /* The hardware cannot generate a 100% duty cycle */
> >         frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> > +       frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
>
> Shouldn't the inversion be done before the hardware limitation fixup?
I think your inference is correct, I will use it.

thanks a lot.
>
> >
> >         mutex_lock(&ddata->lock);
> >         if (state->period != ddata->approx_period) {
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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