# Re: \[PATCHv3\] pwm\_backlight: pass correct brightness to callback

- From: Thierry Reding \<hidden\>
- Date: 2012-07-09 06:30:12 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2012/07/3890493
- Thread: https://ratatoskr.run/linux-fbdev/2012/07/3890460/t.md

```text
On Mon, Jul 09, 2012 at 03:04:23PM +0900, Alexandre Courbot wrote:
> pwm_backlight_update_status calls the notify() and notify_after()
> callbacks before and after applying the new PWM settings. However, if
> brightness levels are used, the brightness value will be changed from
> the index into the levels array to the PWM duty cycle length before
> being passed to notify_after(), which results in inconsistent behavior.
> 
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
>  drivers/video/backlight/pwm_bl.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)

Applied, with a minor stylistic fixup adding a blank line after the
duty_cycle variable declaration. Thanks.

Thierry

> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index 057389d..be48517 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -54,14 +54,17 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
>  		pwm_config(pb->pwm, 0, pb->period);
>  		pwm_disable(pb->pwm);
>  	} else {
> +		int duty_cycle;
>  		if (pb->levels) {
> -			brightness = pb->levels[brightness];
> +			duty_cycle = pb->levels[brightness];
>  			max = pb->levels[max];
> +		} else {
> +			duty_cycle = brightness;
>  		}
>  
> -		brightness = pb->lth_brightness +
> -			(brightness * (pb->period - pb->lth_brightness) / max);
> -		pwm_config(pb->pwm, brightness, pb->period);
> +		duty_cycle = pb->lth_brightness +
> +		     (duty_cycle * (pb->period - pb->lth_brightness) / max);
> +		pwm_config(pb->pwm, duty_cycle, pb->period);
>  		pwm_enable(pb->pwm);
>  	}
>  
> -- 
> 1.7.11.1
> 
> 
> 
```

## Attachments

- [(unnamed)](https://ratatoskr.run/linux-fbdev/2012/07/3890493/attachment/0) (application/pgp-signature, 836 bytes)