linux-kernel - Re: [PATCH v4] pwm: rzg2l-gpt: Reinitialize the cache value in rzg2l_gpt

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Message-ID: <4xwhsp76tb6dn64n7nvyok5j4x5a3jbuovyqdrfvky5iz7rrih@ll4gpo67vn2i>
Date: Tue, 18 Nov 2025 23:24:28 +0100
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>, "stable@...nel.org" <stable@...nel.org>
Subject: Re: [PATCH v4] pwm: rzg2l-gpt: Reinitialize the cache value in
 rzg2l_gpt_disable()

Hello Biju,

On Tue, Nov 18, 2025 at 05:03:34PM +0000, Biju Das wrote:
> > On Fri, Nov 14, 2025 at 02:56:01PM +0000, Biju wrote:
> > > diff --git a/drivers/pwm/pwm-rzg2l-gpt.c b/drivers/pwm/pwm-rzg2l-gpt.c
> > > index 360c8bf3b190..ab91bfd7da48 100644
> > > --- a/drivers/pwm/pwm-rzg2l-gpt.c
> > > +++ b/drivers/pwm/pwm-rzg2l-gpt.c
> > > @@ -190,8 +190,17 @@ static void rzg2l_gpt_disable(struct rzg2l_gpt_chip *rzg2l_gpt,
> > >  	/* Stop count, Output low on GTIOCx pin when counting stops */
> > >  	rzg2l_gpt->channel_enable_count[ch]--;
> > >
> > > -	if (!rzg2l_gpt->channel_enable_count[ch])
> > > +	if (!rzg2l_gpt->channel_enable_count[ch]) {
> > >  		rzg2l_gpt_modify(rzg2l_gpt, RZG2L_GTCR(ch), RZG2L_GTCR_CST, 0);
> > > +		/*
> > > +		 * The rzg2l_gpt_config() test the rzg2l_gpt->period_tick
> > > +		 * variable. This check is not valid, if enabling of a channel
> > > +		 * happens after disabling all the channels as it test against
> > > +		 * the cached value. Therefore, reinitialize the variable
> > > +		 * rzg2l_gpt->period_tick to 0.
> > > +		 */
> > > +		rzg2l_gpt->period_ticks[ch] = 0;
> > > +	}
> > 
> > I think this is wrong. rzg2l_gpt_config() has:
> > 
> >         if (rzg2l_gpt->channel_request_count[ch] > 1) {
> >                 if (period_ticks < rzg2l_gpt->period_ticks[ch])
> >                         return -EBUSY;
> >                 else
> >                         period_ticks = rzg2l_gpt->period_ticks[ch];
> >         }
> > 
> > So if both PWMs of channel `ch` are requested but disabled, rzg2l_gpt->period_ticks[ch] is 0 so you
> > assign
> > 
> > 	period_ticks = rzg2l_gpt->period_ticks[ch];
> > 
> > . In that case however you don't want to change period_ticks, right?
> 
> 
> Yes, what about adding the check that won't allow to set 0 period in this case.
> 
> if ((rzg2l_gpt->channel_request_count[ch] > 1) && rzg2l_gpt->period_ticks[ch])

I think the easy to understand and obviously correct™ check would be: 

	if (rzg2l_gpt->enabled[ch][othersubchannel]) {
		if (period_ticks < rzg2l_gpt->period_ticks[ch])
			return -EBUSY;
		else
			period_ticks = rzg2l_gpt->period_ticks[ch];
	}

(Instead of tracking enabled[ch][subchannel], reading the respective
register is another option.)

Best regards
Uwe

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