linux-kernel - Re: [PATCH v9 2/3] pwm: sifive: change the PWM algorithm

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Message-ID: <CAHh=Yk8MXy73d8M1J5bVu4spDMbjQDneVTqA=Ts=SGPDO7PXMQ@mail.gmail.com>
Date: Tue, 2 Apr 2024 10:08:08 +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 2/3] pwm: sifive: change the PWM algorithm

Uwe Kleine-König <u.kleine-koenig@...gutronix.de> 於 2024年3月19日 週二 上午2:16寫道：
>
> On Thu, Feb 22, 2024 at 04:12:30PM +0800, Nylon Chen wrote:
> > The `frac` variable represents the pulse inactive time, and the result
> > of this algorithm is the pulse active time.
> > Therefore, we must reverse the result.
> >
> > The reference is SiFive FU740-C000 Manual[0]
> >
> > Link: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf [0]
> >
> > Co-developed-by: Zong Li <zong.li@...ive.com>
> > Signed-off-by: Zong Li <zong.li@...ive.com>
> > Co-developed-by: Vincent Chen <vincent.chen@...ive.com>
> > Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
> > Signed-off-by: Nylon Chen <nylon.chen@...ive.com>
> > ---
> >  drivers/pwm/pwm-sifive.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> > index eabddb7c7820..a586cfe4191b 100644
> > --- a/drivers/pwm/pwm-sifive.c
> > +++ b/drivers/pwm/pwm-sifive.c
> > @@ -110,9 +110,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> >                               struct pwm_state *state)
> >  {
> >       struct pwm_sifive_ddata *ddata = pwm_sifive_chip_to_ddata(chip);
> > -     u32 duty, val;
> > +     u32 duty, val, inactive;
> >
> > -     duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> > +     inactive = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> > +     duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive;
> >
> >       state->enabled = duty > 0;
> >
> > @@ -123,7 +124,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> >       state->period = ddata->real_period;
> >       state->duty_cycle =
> >               (u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH;
> > -     state->polarity = PWM_POLARITY_INVERSED;
> > +     state->polarity = PWM_POLARITY_NORMAL;
> >
> >       return 0;
> >  }
> > @@ -139,7 +140,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >       int ret = 0;
> >       u32 frac;
> >
> > -     if (state->polarity != PWM_POLARITY_INVERSED)
> > +     if (state->polarity != PWM_POLARITY_NORMAL)
> >               return -EINVAL;
> >
> >       cur_state = pwm->state;
> > @@ -159,6 +160,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >       frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
> >       /* The hardware cannot generate a 100% duty cycle */
>
> Is this still true now that we know that PWM_SIFIVE_PWMCMP is the
> inactive time in a period? If you fix that, the same claim in the header
> of the driver needs adaption, too.
I believe the statement is true, but I don't know which part the
driver header file refers to.
>
> >       frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> > +     frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
>
> I like the additional variable in pwm_sifive_get_state(). Can you please
> add one here, too?
got it
>
> >       mutex_lock(&ddata->lock);
> >       if (state->period != ddata->approx_period) {
>
Thank you for taking the time to help me review my implementation.

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