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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Message-ID: <p6rqpx3yrn2ib4ulmby7tbnpbg4bjyt4dt6snrmhuyw6hx6izl@lywssban54et>
Date: Fri, 27 Dec 2024 16:39:19 +0100
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Nylon Chen <nylon7717@...il.com>
Cc: Nylon Chen <nylon.chen@...ive.com>, 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
Subject: Re: [PATCH v9 3/3] pwm: sifive: Fix the error in the idempotent test
 within the pwm_apply_state_debug function

On Tue, Dec 24, 2024 at 04:34:53PM +0800, Nylon Chen wrote:
> Uwe Kleine-König <u.kleine-koenig@...gutronix.de> 於 2024年4月12日 週五 下午3:05寫道：
> >
> > 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
> >
> Hi Uwe,
> I apologize for the significant delay in responding to your query,
> I've now completed a thorough verification of the PWM_DEBUG
> functionality.
> 
> The Period Testing:
> seq 5000 5000 100000 | while read p; do echo $p >
> /sys/class/pwm/pwmchip0/pwm0/period echo "Testing period: $p" done
> 
> The Duty Cycle Testing:
> for percent in 0 25 50 75 100; do duty=$((100000 * percent / 100))
> echo $duty > /sys/class/pwm/pwmchip0/pwm0/duty_cycle done

This is unlikely to find the issues that I have in mind. If doing ~100k
assignments is too much, please keep the +1 step but restrict the
interval.

Best regards
Uwe

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