linux-kernel - Re: [PATCH v9 3/3] pwm: sifive: Fix the error in the idempotent test within the pwm_apply_state

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Date: Tue, 2 Apr 2024 10:01:39 +0800
From: Nylon Chen <nylon.chen@...ive.com>
To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org, conor@...nel.org, 
	robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, palmer@...belt.com, 
	paul.walmsley@...ive.com, aou@...s.berkeley.edu, thierry.reding@...il.com, 
	vincent.chen@...ive.com, zong.li@...ive.com, nylon7717@...il.com
Subject: Re: [PATCH v9 3/3] pwm: sifive: Fix the error in the idempotent test
 within the pwm_apply_state_debug function

Uwe Kleine-König <u.kleine-koenig@...gutronix.de> 於 2024年3月19日 週二 上午2:17寫道：
>
> Hello,
>
> On Thu, Feb 22, 2024 at 04:12:31PM +0800, Nylon Chen wrote:
> > 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.
> >
> > e.g.
> > $ echo 110 > /sys/devices/platform/led-controller-1/leds/d12/brightness
> > $ .apply is not idempotent (ena=1 pol=0 1739692/4032985) -> (ena=1 pol=0 1739630/4032985)
> >
> > Co-developed-by: Zong Li <zong.li@...ive.com>
> > Signed-off-by: Zong Li <zong.li@...ive.com>
> > Signed-off-by: Nylon Chen <nylon.chen@...ive.com>
> > ---
> >  drivers/pwm/pwm-sifive.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> > index a586cfe4191b..bebcbebacccd 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);
> >       dev_dbg(ddata->chip.dev,
> >               "New real_period = %u ns\n", ddata->real_period);
> >  }
Hi Uwe
>
> pwm_sifive_apply has a DIV64_U64_ROUND_CLOSEST(). I wonder if that needs
> adaption, too?!
According to my experiments, no adjustment is necessary.
>
> Best regards
> Uwe
>
> --
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |