linux-kernel - Re: [PATCH v2] pwm: rzg2l-gpt: Implementation of the waveform callbacks

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Message-ID: <6gvpdndagee54h7gr3uqm37rfu4yk2owffxwtszyjvnic2vqvl@pbp3jqcfrzox>
Date: Fri, 12 Sep 2025 14:32:24 +0200
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Biju Das <biju.das.jz@...renesas.com>
Cc: "biju.das.au" <biju.das.au@...il.com>, 
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v2] pwm: rzg2l-gpt: Implementation of the waveform
 callbacks

Hello Biju,

On Thu, Sep 11, 2025 at 09:46:38AM +0000, Biju Das wrote:
> > -----Original Message-----
> > From: Uwe Kleine-König <ukleinek@...nel.org>
> > Sent: 09 September 2025 16:19
> > On Thu, Aug 14, 2025 at 12:50:20PM +0100, Biju wrote:
> > > -/* Caller holds the lock while calling rzg2l_gpt_config() */ -static
> > > int rzg2l_gpt_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > > -			    const struct pwm_state *state)
> > > +static int rzg2l_gpt_round_waveform_tohw(struct pwm_chip *chip,
> > > +					 struct pwm_device *pwm,
> > > +					 const struct pwm_waveform *wf,
> > > +					 void *_wfhw)
> > > +
> > >  {
> > >  	struct rzg2l_gpt_chip *rzg2l_gpt = to_rzg2l_gpt_chip(chip);
> > > -	u8 sub_ch = rzg2l_gpt_subchannel(pwm->hwpwm);
> > > +	struct rzg2l_gpt_waveform *wfhw = _wfhw;
> > >  	u8 ch = RZG2L_GET_CH(pwm->hwpwm);
> > >  	u64 period_ticks, duty_ticks;
> > >  	unsigned long pv, dc;
> > > -	u8 prescale;
> > > +
> > > +	guard(mutex)(&rzg2l_gpt->lock);
> > > +	if (wf->period_length_ns == 0) {
> > > +		*wfhw = (struct rzg2l_gpt_waveform){
> > > +			.gtpr = 0,
> > > +			.gtccr = 0,
> > > +			.prescale = 0,
> > > +		};
> > > +
> > > +		return 0;
> > > +	}
> > >
> > >  	/* Limit period/duty cycle to max value supported by the HW */
> > > -	period_ticks = mul_u64_u64_div_u64(state->period, rzg2l_gpt->rate_khz, USEC_PER_SEC);
> > > +	period_ticks = mul_u64_u64_div_u64(wf->period_length_ns,
> > > +rzg2l_gpt->rate_khz, USEC_PER_SEC);
> > >  	if (period_ticks > RZG2L_MAX_TICKS)
> > >  		period_ticks = RZG2L_MAX_TICKS;
> > >  	/*
> > 
> > The code that follows here needs adaption. Other than .apply(),
> > .round_waveform_tohw() is supposed to not fail if the requested period is too small but use the
> > smallest possible value then (and return 1).
> 
> 
> You mean something like below
> 
>         if (rzg2l_gpt->channel_request_count[ch] > 1) {
>                 if (period_ticks < rzg2l_gpt->period_ticks[ch])
> -                       return -EBUSY;
> +                       is_small_second_period = true;
>                 else
>                         period_ticks = rzg2l_gpt->period_ticks[ch];
>         }
> @@ -272,6 +276,9 @@ static int rzg2l_gpt_round_waveform_tohw(struct pwm_chip *chip,
>         wfhw->prescale = rzg2l_gpt_calculate_prescale(rzg2l_gpt, period_ticks);
>         pv = rzg2l_gpt_calculate_pv_or_dc(period_ticks, wfhw->prescale);
>         wfhw->gtpr = pv;
> +       if (is_small_second_period)
> +               return 1;

Just locking at the diff: Yes, that looks about right. I guess you also
need `period_ticks = rzg2l_gpt->period_ticks[ch]` in the
is_small_second_period==true case.

Best regards
Uwe

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