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: Fri, 12 Apr 2024 09:05:32 +0200
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Nylon Chen <nylon.chen@...ive.com>
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

On Tue, Apr 02, 2024 at 10:01:39AM +0800, Nylon Chen wrote:
> 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.

Did you enable PWM_DEBUG and tested with something like:

	seq 5000 100000 | while read p; do echo p > /sys/class/pwm/pwmchipX/pwmY/period; done

and then verified that this test didn't result in kernel messages about
wrong settings?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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