linux-kernel - Re: [PATCH] pwm: lpc32xx

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Date:	Tue, 06 Nov 2012 10:36:16 +0100
From:	Roland Stigge <stigge@...com.de>
To:	Thierry Reding <thierry.reding@...onic-design.de>
CC:	Alban Bedel <alban.bedel@...onic-design.de>,
	linux-kernel@...r.kernel.org,
	Alexandre Pereira da Silva <aletes.xgr@...il.com>
Subject: Re: [PATCH] pwm: lpc32xx - Fix the PWM polarity

On 05/11/12 22:03, Thierry Reding wrote:
> Cc'ing Roland and Alexandre. What do you guys think?
> 
> On Mon, Nov 05, 2012 at 05:48:45PM +0100, Alban Bedel wrote:
>> Signed-off-by: Alban Bedel <alban.bedel@...onic-design.de> --- 
>> drivers/pwm/pwm-lpc32xx.c |    6 +++++- 1 files changed, 5
>> insertions(+), 1 deletions(-)
>> 
>> diff --git a/drivers/pwm/pwm-lpc32xx.c
>> b/drivers/pwm/pwm-lpc32xx.c index adb87f0..a2704b8 100644 ---
>> a/drivers/pwm/pwm-lpc32xx.c +++ b/drivers/pwm/pwm-lpc32xx.c @@
>> -51,7 +51,11 @@ static int lpc32xx_pwm_config(struct pwm_chip
>> *chip, struct pwm_device *pwm,
>> 
>> c = 256 * duty_ns; do_div(c, period_ns); -	duty_cycles = c; +	if
>> (c > 255) +		c = 255; +	if (c < 1) +		c = 1; +	duty_cycles = 256
>> - c;
>> 
>> writel(PWM_ENABLE | PWM_RELOADV(period_cycles) |
>> PWM_DUTY(duty_cycles), lpc32xx->base + (pwm->hwpwm << 2));
> 
> Shouldn't duty_cycles rather be 255 - c, such that it can still be
> 0?
> 
> Thierry

According to the Manual: [Low]/[High] = [PWM_DUTY] / [256-PWM_DUTY],
i.e., the PWM polarity inversion looks good.

However, as Thierry pointed out, the valid range 0..255 should be
maintained differently, maybe:

if (c > 255)
	c = 255;
duty_cycles = 255 - c;

?

Thanks,

Roland
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