linux-kernel - Re: [PATCH] pwm: imx-tpm: Use correct MODULO value for EPWM mode

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Message-ID: <ZxkXwTXwfkC9W5C3@lizhi-Precision-Tower-5810>
Date: Wed, 23 Oct 2024 11:35:29 -0400
From: Frank Li <Frank.li@....com>
To: Erik Schumacher <erik.schumacher@...s-sensing.com>
Cc: "ukleinek@...nel.org" <ukleinek@...nel.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>
Subject: Re: [PATCH] pwm: imx-tpm: Use correct MODULO value for EPWM mode

On Wed, Oct 23, 2024 at 12:33:53PM +0000, Erik Schumacher wrote:
> The modulo register defines the period of the edge-aligned PWM mode
> (which is the only mode implemented). The reference manual states:
> "The EPWM period is determined by (MOD + 0001h) ..." So the value that
> is written to the MOD register must therefore be one less than the
> calculated period length.
> A correct MODULO value is particularly relevant if the PWM has to output
> a high frequency due to a low period value.
>
This is bug fix,  add fix tag and cc stable

Frank

> Signed-off-by: Erik Schumacher <erik.schumacher@...s-sensing.com>
> ---
>  drivers/pwm/pwm-imx-tpm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c
> index 96ea343856f0..a05b66ffe208 100644
> --- a/drivers/pwm/pwm-imx-tpm.c
> +++ b/drivers/pwm/pwm-imx-tpm.c
> @@ -106,7 +106,7 @@ static int pwm_imx_tpm_round_state(struct pwm_chip *chip,
>  	p->prescale = prescale;
>
>  	period_count = (clock_unit + ((1 << prescale) >> 1)) >> prescale;
> -	p->mod = period_count;
> +	p->mod = period_count - 1;
>
>  	/* calculate real period HW can support */
>  	tmp = (u64)period_count << prescale;
> --
> 2.47.0
>