[PATCH v2 4/5] drm/amd/display: Add support for custom brightness curve

[Alex Hung]

Reviewed-by: Alex Hung <alex.hung at amd.com>

On 2/28/25 11:51, Mario Limonciello wrote:
> Some systems specify in the firmware a brightness curve that better
> reflects the characteristics of the panel used. This is done in the
> form of data points and matching luminance percentage.
> 
> When converting a userspace requested brightness value use that curve
> to convert to a firmware intended brightness value.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
> ---
>   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 25 +++++++++++++++++++
>   1 file changed, 25 insertions(+)
> 
> 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 61d626914590..b252c67f2bc4 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -4759,10 +4759,35 @@ static u32 convert_brightness_from_user(const struct amdgpu_dm_backlight_caps *c
>   					uint32_t brightness)
>   {
>   	unsigned int min, max;
> +	u8 prev_signal = 0, prev_lum = 0;
>   
>   	if (!get_brightness_range(caps, &min, &max))
>   		return brightness;
>   
> +	for (int i = 0; i < caps->data_points; i++) {
> +		u8 signal, lum;
> +
> +		signal = caps->luminance_data[i].input_signal;
> +		lum = caps->luminance_data[i].luminance;
> +
> +		/*
> +		 * brightness == signal: luminance is percent numerator
> +		 * brightness < signal: interpolate between previous and current luminance numerator
> +		 * brightness > signal: find next data point
> +		 */
> +		if (brightness < signal)
> +			lum = prev_lum + DIV_ROUND_CLOSEST((lum - prev_lum) *
> +							   (brightness - prev_signal),
> +							   signal - prev_signal);
> +		else if (brightness > signal) {
> +			prev_signal = signal;
> +			prev_lum = lum;
> +			continue;
> +		}
> +		brightness = DIV_ROUND_CLOSEST(lum * brightness, 101);
> +		break;
> +	}
> +
>   	// Rescale 0..255 to min..max
>   	return min + DIV_ROUND_CLOSEST((max - min) * brightness,
>   				       AMDGPU_MAX_BL_LEVEL);