[PATCH] drm/amd: Don't fail on backlight = 0

[Wentland, Harry]

On 2018-11-06 11:14 a.m., David Francis wrote:
> Amgpu's backlight update status function was
> returning 1 (an error value) when the backlight
> property was 0.  This breaks users that assume
> 0 is a valid backlight value (which is a
> correct assumption)
> 
> If the user passes in a backlight value of 0,
> tell them everything is fine, then write a value of
> 1 to hardware.
> 
> Signed-off-by: David Francis <David.Francis at amd.com>

Reviewed-by: Harry Wentland <harry.wentland at amd.com>

Harry

> Bugzilla: https://bugs.freedesktop.org/108668
> Fixes: 416615ea9578 ("drm/amd/display: set backlight level limit to 1")
> Cc: Suresh.Guttula at amd.com
> Cc: Harry.Wentland at amd.com
> Cc: Samantham at posteo.net
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c  | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index f8ec8a146663..131e6483d442 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -1567,21 +1567,23 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
>  {
>  	struct amdgpu_display_manager *dm = bl_get_data(bd);
>  
> +	/* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
> +	 * and 16 bit fractional, where 1.0 is max backlight value.
> +	 * bd->props.brightness is 8 bit format and needs to be converted by
> +	 * scaling via copy lower byte to upper byte of 16 bit value.
> +	 */
> +	uint32_t brightness = bd->props.brightness * 0x101;
> +
>  	/*
>  	 * PWM interperts 0 as 100% rather than 0% because of HW
> -	 * limitation for level 0.So limiting minimum brightness level
> +	 * limitation for level 0.  So limiting minimum brightness level
>  	 * to 1.
>  	 */
>  	if (bd->props.brightness < 1)
> -		return 1;
> +		brightness = 0x101;
>  
> -	/* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
> -	 * and 16 bit fractional, where 1.0 is max backlight value.
> -	 * bd->props.brightness is 8 bit format and needs to be converted by
> -	 * scaling via copy lower byte to upper byte of 16 bit value.
> -	 */
>  	if (dc_link_set_backlight_level(dm->backlight_link,
> -			(bd->props.brightness * 0x101), 0, 0))
> +			brightness, 0, 0))
>  		return 0;
>  	else
>  		return 1;
>