linux-kernel - [PATCH 2/2] PWM: atmel: correct CDTY calculation

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Message-Id: <1394806749-29778-3-git-send-email-alexandre.belloni@free-electrons.com>
Date:	Fri, 14 Mar 2014 15:19:09 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Bo Shen <voice.shen@...el.com>, linux-pwm@...r.kernel.org,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: [PATCH 2/2] PWM: atmel: correct CDTY calculation

>From the datasheet, the actual duty cycle is:
(period - (1/clk) * CDTY)/period

This actually correct the polarity of the PWM and solves the issue that pwm-leds
exhibits: when setting a duty cycle of 0 and then disabling a channel, the level
was wrong (1 when the polarity was normal and 0 when the polarity was inversed).

Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
---
 drivers/pwm/pwm-atmel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
index 2d69e9c431dd..0adc952cc4ef 100644
--- a/drivers/pwm/pwm-atmel.c
+++ b/drivers/pwm/pwm-atmel.c
@@ -133,7 +133,7 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	prd = div;
 	div *= duty_ns;
 	do_div(div, period_ns);
-	dty = div;
+	dty = prd - div;
 
 	ret = clk_enable(atmel_pwm->clk);
 	if (ret) {
-- 
1.8.3.2

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