linux-kernel - Re: pwm: atmel: problem when disable pwm

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Date:	Wed, 4 Jun 2014 17:05:49 +0200
From:	Raphaël Poggi <raphio98@...il.com>
To:	Thierry Reding <thierry.reding@...il.com>,
	linux-kernel@...r.kernel.org, inux-pwm@...r.kernel.org
Subject: Re: pwm: atmel: problem when disable pwm

Hello,

Thanks for your answer.

I'm seeing the problem with the version 3.10-at91. I tried with the
newer version of the driver which add the 916030db4399 commit and I
have the same bug.

2014-06-04 16:46 GMT+02:00 Thierry Reding <thierry.reding@...il.com>:
> Adding in the linux-pwm mailing list.
>
> On Wed, Jun 04, 2014 at 02:56:13PM +0200, Raphaël Poggi wrote:
>> Hello,
>>
>> I'm using the pwm-atmel driver to control led, but i'm facing a problem.
>>
>> When writing "echo 0 > /sys/class/leds/d1/brightness" (to switch off
>> the led) sometimes the led stayed active.
>>
>> After investigation I think this problem is due to this function:
>>
>> static void atmel_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>> {
>>     struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
>>
>>     atmel_pwm_writel(atmel_pwm, PWM_DIS, 1 << pwm->hwpwm);
>>
>>     clk_disable(atmel_pwm->clk);
>> }
>>
>> By disable the pwm channel, I think the duty cycle "0" has not been
>> update, and the channel is disable and stayed in active state (high or
>> low depending of polarity).
>
> This sounds like a bug that could be fixed by this commit:
>
>         916030db4399 pwm: atmel: correct CDTY calculation
>
> What version of the kernel are you seeing this problem with? The above
> commit was first added in v3.15-rc1, so maybe try that or any later
> version to see if that fixes it.
>
> Thierry
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