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Date: Fri, 12 Apr 2024 09:05:32 +0200
From: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To: Nylon Chen <nylon.chen@sifive.com>
Cc: linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org, conor@kernel.org, robh+dt@kernel.org, 
	krzysztof.kozlowski+dt@linaro.org, palmer@dabbelt.com, paul.walmsley@sifive.com, 
	aou@eecs.berkeley.edu, thierry.reding@gmail.com, vincent.chen@sifive.com, 
	zong.li@sifive.com, nylon7717@gmail.com
Subject: Re: [PATCH v9 3/3] pwm: sifive: Fix the error in the idempotent test
 within the pwm_apply_state_debug function
Message-ID: <xf6ympnaljfjztptb5w5qdpuluckptozdz5a7gtuycsev32ngr@x2ovibqv6evr>
References: <20240222081231.213406-1-nylon.chen@sifive.com>
 <20240222081231.213406-4-nylon.chen@sifive.com>
 <jvwgsszvs4jtcytcphsdjulzgqfqzdp4sisu236ddwsqgmvriw@ngi4ljgh5b74>
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On Tue, Apr 02, 2024 at 10:01:39AM +0800, Nylon Chen wrote:
> Uwe Kleine-K=C3=B6nig <u.kleine-koenig@pengutronix.de> =E6=96=BC 2024=E5=
=B9=B43=E6=9C=8819=E6=97=A5 =E9=80=B1=E4=BA=8C =E4=B8=8A=E5=8D=882:17=E5=AF=
=AB=E9=81=93=EF=BC=9A
> >
> > 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/brightne=
ss
> > > $ .apply is not idempotent (ena=3D1 pol=3D0 1739692/4032985) -> (ena=
=3D1 pol=3D0 1739630/4032985)
> > >
> > > Co-developed-by: Zong Li <zong.li@sifive.com>
> > > Signed-off-by: Zong Li <zong.li@sifive.com>
> > > Signed-off-by: Nylon Chen <nylon.chen@sifive.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_si=
five_ddata *ddata,
> > >
> > >       /* As scale <=3D 15 the shift operation cannot overflow. */
> > >       num =3D (unsigned long long)NSEC_PER_SEC << (PWM_SIFIVE_CMPWIDT=
H + scale);
> > > -     ddata->real_period =3D div64_ul(num, rate);
> > > +     ddata->real_period =3D DIV_ROUND_UP_ULL(num, rate);
> > >       dev_dbg(ddata->chip.dev,
> > >               "New real_period =3D %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/p=
eriod; done

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

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=C3=B6nig         =
   |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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