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

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Message-ID: <91bfd0c1726d2e6d10c96a3f2e141a7315b08467.camel@iris-sensing.com>
Date: Thu, 24 Oct 2024 06:41:07 +0000
From: Erik Schumacher <erik.schumacher@...s-sensing.com>
To: "ukleinek@...nel.org" <ukleinek@...nel.org>
CC: "anson.huang@....com" <anson.huang@....com>, "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: [PATCH v2] pwm: imx-tpm: Use correct MODULO value for EPWM mode

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>
---
v2:
 - Add Fixes: and Cc: tags

 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