linux-kernel - [PATCH 1/3] pwm: lpc32xx

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Message-Id: <1352894295-14339-2-git-send-email-alban.bedel@avionic-design.de>
Date:	Wed, 14 Nov 2012 12:58:13 +0100
From:	Alban Bedel <alban.bedel@...onic-design.de>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	linux-kernel@...r.kernel.org, Roland Stigge <stigge@...com.de>,
	Alexandre Pereira da Silva <aletes.xgr@...il.com>,
	Alban Bedel <alban.bedel@...onic-design.de>
Subject: [PATCH 1/3] pwm: lpc32xx - Fix the PWM polarity

The duty cycles value goes from 1 (99% HIGH) to 256 (0% HIGH) but it
is stored modulo 256 in the register as it is only 8 bits wide.

Signed-off-by: Alban Bedel <alban.bedel@...onic-design.de>
---
 drivers/pwm/pwm-lpc32xx.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/drivers/pwm/pwm-lpc32xx.c b/drivers/pwm/pwm-lpc32xx.c
index adb87f0..03ec3ff 100644
--- a/drivers/pwm/pwm-lpc32xx.c
+++ b/drivers/pwm/pwm-lpc32xx.c
@@ -49,9 +49,24 @@ static int lpc32xx_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 		c = 0; /* 0 set division by 256 */
 	period_cycles = c;
 
+	/* The duty value is a follow:
+	 *
+	 *  DUTY     HIGH LEVEL
+	 *   1         99.9%
+	 *   25        90.0%
+	 *   128       50.0%
+	 *   220       10.0%
+	 *   255        0.1%
+	 *   0          0.0%
+	 *
+	 * In other word the in-register value is duty % 256 with duty
+	 * in the range 1-256.
+	 */
 	c = 256 * duty_ns;
 	do_div(c, period_ns);
-	duty_cycles = c;
+	if (c > 255)
+		c = 255;
+	duty_cycles = 256 - c;
 
 	writel(PWM_ENABLE | PWM_RELOADV(period_cycles) | PWM_DUTY(duty_cycles),
 		lpc32xx->base + (pwm->hwpwm << 2));
-- 
1.7.0.4

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