Re: [v5 2/2] pwm: sifive: change the PWM controlled LED algorithm

Uwe Kleine-König
2024-01-08T09:44:51Z

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Hello Nylon,

On Mon, Jan 08, 2024 at 04:27:40PM +0800, Nylon Chen wrote:
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 於 2023年12月12日 週二 上午4:50寫道：
> > On Tue, Oct 24, 2023 at 06:19:02PM +0800, Nylon Chen wrote:
> > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> > > index eabddb7c7820..353c2342fbf1 100644
> > > --- a/drivers/pwm/pwm-sifive.c
> > > +++ b/drivers/pwm/pwm-sifive.c
> > > @@ -101,7 +101,7 @@ static void pwm_sifive_update_clock(struct pwm_sifive_ddata *ddata,
> > >
> > > /* As scale <= 15 the shift operation cannot overflow. */
> > > num = (unsigned long long)NSEC_PER_SEC << (PWM_SIFIVE_CMPWIDTH + scale);
> > > - ddata->real_period = div64_ul(num, rate);
> > > + ddata->real_period = DIV_ROUND_UP_ULL(num, rate);
> >
> > It's unclear to me, why you changed that.
> Because there is a gap in idempotent tests.
> e.g.
> root@unmatched:~# echo 110 >
> /sys/devices/platform/led-controller-1/leds/d12/brightness
> [ 706.987712] .apply is not idempotent (ena=1 pol=0 1739692/4032985)
> -> (ena=1 pol=0 1739630/4032985)
> root@unmatched:~# echo 120 >
> /sys/devices/platform/led-controller-1/leds/d12/brightness
> [ 709.817554] .apply is not idempotent (ena=1 pol=0 1897846/4032985)
> -> (ena=1 pol=0 1897784/4032985)
>
> Round the result to the nearest whole number. This ensures that
> real_period is always a reasonable integer that is not lower than the
> actual value.
>
> After modification, idempotent errors can be avoided.

That's very welcome, however I think this should be a separate change.

I'll think about the rest of your changes when you send a new patch.

Best regards
Uwe

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