linux-kernel - RE: [PATCH 1/1] PWM-atmel: Fixed a bug which set the pwm clock prescaler incorrectly. In the defect code the prescaler was always one more than expected value, which resulted in the pwm output with wrong frequency and duty cycle.

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Message-ID: <D68D4F79CA301E4CB7967E4AF0038407253158D1@DHRNASVXM01.danaher.org>
Date:	Thu, 25 Sep 2014 14:44:48 +0000
From:	"Yang, Robert" <RYang@...h.com>
To:	Thierry Reding <thierry.reding@...il.com>,
	"hachyang@...il.com" <hachyang@...il.com>
CC:	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nikolaus Voss <n.voss@...nmann-emt.de>
Subject: RE: [PATCH 1/1] PWM-atmel: Fixed a bug which set the pwm clock
 prescaler incorrectly. In the defect code the prescaler was always one more
 than expected value, which resulted in the pwm output with wrong frequency
 and duty cycle.

Hi Thierry,

I agree Nikolaus's fix is more efficient and works too.

Robert

-----Original Message-----
From: Thierry Reding [mailto:thierry.reding@...il.com]
Sent: Thursday, September 25, 2014 1:55 AM
To: hachyang@...il.com
Cc: linux-pwm@...r.kernel.org; linux-kernel@...r.kernel.org; Yang, Robert; Nikolaus Voss
Subject: Re: [PATCH 1/1] PWM-atmel: Fixed a bug which set the pwm clock prescaler incorrectly. In the defect code the prescaler was always one more than expected value, which resulted in the pwm output with wrong frequency and duty cycle.

On Wed, Sep 10, 2014 at 03:35:19PM -0600, hachyang@...il.com wrote:
> From: ryang <ryang@...h.com>
>
> Signed-off-by: ryang <ryang@...h.com>
> ---
>  drivers/pwm/pwm-atmel.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c index
> 6e700a5..2dca0bf 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -128,7 +128,8 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>                       return -EINVAL;
>               }
>       }
> -
> +     /* Need to reduce the prescaler by 1 */
> +     pres--;
>       /* Calculate the duty cycles */
>       prd = div;
>       div *= duty_ns;
> --
> 1.9.1

I think this was fixed by a different patch by Nikolaus in a more direct way, see: https://lkml.org/lkml/2014/9/24/28

I've pushed that patch to the for-next branch of the PWM tree. Can you verify that the issue you were seeing is gone?

Thierry
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