drm/amd/display: Add support for custom brightness curve

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.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Link: https://lore.kernel.org/r/20250228185145.186319-5-mario.limonciello@amd.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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 8d5daa96eeaead80c48308af774f7821e171fd48..5e049b8f877dcee80d4bcb6deba774187f7f4169 100644 (file)
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4750,10 +4750,35 @@ 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);