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

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Message-ID:
 <TY3PR01MB1134679D611D611AC2CED72F886D6A@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Tue, 18 Nov 2025 17:03:34 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Uwe Kleine-König <ukleinek@...nel.org>, biju.das.au
	<biju.das.au@...il.com>
CC: "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()

Hi Uwe,

Thanks for the feedback.

> -----Original Message-----
> From: Uwe Kleine-König <ukleinek@...nel.org>
> Sent: 17 November 2025 08:00
> Subject: Re: [PATCH v4] pwm: rzg2l-gpt: Reinitialize the cache value in rzg2l_gpt_disable()
> 
> Hello Biju,
> 
> On Fri, Nov 14, 2025 at 02:56:01PM +0000, Biju wrote:
> > From: Biju Das <biju.das.jz@...renesas.com>
> >
> > 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 in
> > rzg2l_gpt_disable(), when all the logical channels of a hardware channel is disabled.
> >
> > Cc: stable@...nel.org
> > Fixes: 061f087f5d0b ("pwm: Add support for RZ/G2L GPT")
> > Signed-off-by: Biju Das <biju.das.jz@...renesas.com>
> > ---
> > v3->v4:
> >  * Split the patch as separate from [1] for easy merging.
> >  * Updated commit description
> >  * Added comments about the fix in rzg2l_gpt_disable()
> > v3:
> >  * New patch
> >
> > [1]
> > https://lore.kernel.org/all/20250915163637.3572-1-biju.das.jz@bp.renes
> > as.com/#t
> > ---
> >  drivers/pwm/pwm-rzg2l-gpt.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > 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])


Cheers,
Biju