linux-kernel - Re: [PATCH 1/9] backlight: atmel-pwm-bl: fix reported brightness

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Date:	Wed, 23 Oct 2013 10:20:59 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Johan Hovold' <jhovold@...il.com>
Cc:	'Richard Purdie' <rpurdie@...ys.net>,
	'Nicolas Ferre' <nicolas.ferre@...el.com>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, 'Jingoo Han' <jg1.han@...sung.com>
Subject: Re: [PATCH 1/9] backlight: atmel-pwm-bl: fix reported brightness

On Wednesday, October 23, 2013 2:27 AM, Johan Hovold wrote:
> 
> The driver supports 16-bit brightness values, but the value returned
> from get_brightness was truncated to eight bits.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Johan Hovold <jhovold@...il.com>
> ---
>  drivers/video/backlight/atmel-pwm-bl.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/backlight/atmel-pwm-bl.c b/drivers/video/backlight/atmel-pwm-bl.c
> index 66885fb..8aac273 100644
> --- a/drivers/video/backlight/atmel-pwm-bl.c
> +++ b/drivers/video/backlight/atmel-pwm-bl.c
> @@ -70,7 +70,7 @@ static int atmel_pwm_bl_set_intensity(struct backlight_device *bd)
>  static int atmel_pwm_bl_get_intensity(struct backlight_device *bd)
>  {
>  	struct atmel_pwm_bl *pwmbl = bl_get_data(bd);
> -	u8 intensity;
> +	u32 intensity;
> 
>  	if (pwmbl->pdata->pwm_active_low) {
>  		intensity = pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY) -
> @@ -80,7 +80,7 @@ static int atmel_pwm_bl_get_intensity(struct backlight_device *bd)
>  			pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY);
>  	}
> 
> -	return intensity;
> +	return (u16)intensity;

However, atmel_pwm_bl_get_intensity() should return 'int',
instead of 'u16'. Also, pwm_channel_readl() returns 'u32'.

Then, how about the following?

--- a/drivers/video/backlight/atmel-pwm-bl.c
+++ b/drivers/video/backlight/atmel-pwm-bl.c
@@ -70,17 +70,17 @@ static int atmel_pwm_bl_set_intensity(struct backlight_device *bd)
 static int atmel_pwm_bl_get_intensity(struct backlight_device *bd)
 {
	struct atmel_pwm_bl *pwmbl = bl_get_data(bd);
-	u8 intensity;
+	u16 intensity;

	if (pwmbl->pdata->pwm_active_low) {
-		intensity = pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY) -
+		intensity = (u16) pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY) -
			pwmbl->pdata->pwm_duty_min;
	} else {
-		intensity = pwmbl->pdata->pwm_duty_max -
+		intensity = (u16) pwmbl->pdata->pwm_duty_max -
			pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY);
	}

-	return intensity;
+	return (int)intensity;
 }

Best regards,
Jingoo Han

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