linux-kernel - Re: [PATCH v2] pwm: imx-tpm: Use correct MODULO value for EPWM mode

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Message-ID: <wqjwdjqsjn5yngbkdpbinwtonxdpugy6n6nide7fcodhpto4hh@7yxigtrvvu2n>
Date: Thu, 24 Oct 2024 23:01:31 +0200
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Erik Schumacher <erik.schumacher@...s-sensing.com>
Cc: "kernel@...gutronix.de" <kernel@...gutronix.de>, 
	"thierry.reding@...il.com" <thierry.reding@...il.com>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>, 
	"festevam@...il.com" <festevam@...il.com>, "shawnguo@...nel.org" <shawnguo@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>, 
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v2] pwm: imx-tpm: Use correct MODULO value for EPWM mode

Hello,

[dropping anson.huang@....com from Cc]

On Thu, Oct 24, 2024 at 06:41:07AM +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.
> 
> Fixes: 738a1cfec2ed ("pwm: Add i.MX TPM PWM driver support")
> Cc: stable@...r.kernel.org
> 
> Signed-off-by: Erik Schumacher <erik.schumacher@...s-sensing.com>

No empty line between these trailer lines please.

> 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;

This looks bogus if period_count is 0.

Best regards
Uwe

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