linux-kernel - Re: [PATCH v4 2/2] pwm: sophgo: add pwm support for Sophgo CV1800 SoC

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Message-ID: <CAJRtX8RagduSxqxh-jH2wcoNgzbRdNRYW5Gcka1_uPR-o-Tj7w@mail.gmail.com>
Date: Tue, 12 Mar 2024 16:07:30 +0800
From: Jingbao Qiu <qiujingbao.dlmu@...il.com>
To: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc: robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, 
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, 
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	dlan@...too.org, inochiama@...look.com
Subject: Re: [PATCH v4 2/2] pwm: sophgo: add pwm support for Sophgo CV1800 SoC

Hi Uwe,

Gentle ping,
I'm sorry for wasting your time, and I look forward to your feedback.

> > > +     if (tem < PWM_CV1800_MINPERIOD)
> > > +             return -EINVAL;
> > > +
> > > +     if (tem > PWM_CV1800_MAXPERIOD)
> > > +             tem = PWM_CV1800_MAXPERIOD;
> > > +
> > > +     period_val = (u32)tem;
> > > +
> > > +     /*
> > > +      * The meaning of HLPERIOD is the number of beats in the low or high level
> > > +      * of the PERIOD. When the value of the POLARITY register is 0, HLPERIOD
> > > +      * represents a low level.
> > > +      * HLPERIOD = period_val - rate(MHz) / duty(MHz)
> > > +      * HLPERIOD = period_val - duty(ns) * rate(Hz) / NSEC_PER_SEC
> >
> > So HLPERIOD defines the second part of each period, right? This isn't
> > considered in .get_state().
>
> I am so sorry about this. I made a mess of the duty cycle.
> According to the PWM_DEBUG, it can be inferred that configure the
> biggest duty_cycle not
> bigger than the requested value, so in .apply duty_cycle should round down and
> in .get_state duty_cycle should round up. However, when the polarity is normal,
> This hardware requires a low-level beat count. So the corrected code
> is as follows.
>
> in .apply()
>
> ticks = mul_u64_u64_div_u64(state->duty_cycle , priv->clk_rate,NSEC_PER_SEC);
> ...
> hlperiod_val =period_val- (u32)ticks;
>
> in .get_state()
>
> u32 hlperiod_val=0;
>
> period_ns = DIV_ROUND_UP_ULL(period_val * NSEC_PER_SEC,priv->clk_rate);
> duty_ns = DIV_ROUND_UP_ULL(hlperiod_val * period_ns, period_val);
> hlperiod_val = period_ns - duty_ns;
>
> I tested this code with PWM_DEBUG. no warning output. What do you
> think about this?
>
>

in .apply()

ticks = mul_u64_u64_div_u64(state->duty_cycle, priv->clk_rate,
NSEC_PER_SEC);
if (ticks > period_val)
ticks = period_val;

hlperiod_val = period_val - (u32)ticks;
..
regmap_write(priv->map, PWM_CV1800_HLPERIOD(pwm->hwpwm), hlperiod_val);

in .get_state()

u64 hlperiod_ns = 0;
regmap_read(priv->map, PWM_CV1800_HLPERIOD(pwm->hwpwm), &hlperiod_val);
..
period_ns = DIV_ROUND_UP_ULL(period_val * NSEC_PER_SEC,
priv->clk_rate);
hlperiod_ns = DIV_ROUND_UP_ULL(hlperiod_val * NSEC_PER_SEC,
priv->clk_rate);

duty_ns = period_ns - hlperiod_ns;

I tested this code with PWM_DEBUG. no warning output.

> >
> > > +      */
> > > +     tem = mul_u64_u64_div_u64(state->duty_cycle, priv->clk_rate,
> > > +                               NSEC_PER_SEC);
> > > +     if (tem > period_val)
> > > +             return -EINVAL;
> >
> > if (tem > period_val)
> >         tem = period_val;
> >
> > > +     hlperiod_val = period_val - (u32)tem;
> >
> > Wrong rounding I think. Did you test your driver with PWM_DEBUG enabled?
>
> ditto.
>

Best regards
Jingbao Qiu