On 8/13/26 12:09, Akhmed Zhitaev wrote:
Custom brightness curves use an 8-bit input signal. After exporting the full PWM range to userspace, the curve normalizer still divides requests by the physical PWM span. On panels with a nonzero minimum PWM level, this can produce a curve input greater than 255 and send an invalid backlight level to DC. Scale the userspace [0..max] range to the curve's [0..255] range instead. This retains the full advertised range and keeps the reverse readback conversion unchanged. Fixes: 8dbd72cb7900 ("drm/amd/display: Export full brightness range to userspace") Cc: [email protected] Signed-off-by: Akhmed Zhitaev <[email protected]> --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 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 40d82a3ee..533c69f0b 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -5131,10 +5131,10 @@ static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps, return 1; }-/* Rescale from [min..max] to [0..AMDGPU_MAX_BL_LEVEL] */-static inline u32 scale_input_to_fw(int min, int max, u64 input) +/* Rescale userspace [0..max] to the firmware curve's [0..255]. */ +static inline u32 scale_input_to_fw(int max, u64 input) { - return DIV_ROUND_CLOSEST_ULL(input * AMDGPU_MAX_BL_LEVEL, max - min); + return DIV_ROUND_CLOSEST_ULL(input * AMDGPU_MAX_BL_LEVEL, max); }/* Rescale from [0..AMDGPU_MAX_BL_LEVEL] to [min..max] */@@ -5147,7 +5147,7 @@ static void convert_custom_brightness(const struct amdgpu_dm_backlight_caps *cap unsigned int min, unsigned int max, uint32_t *user_brightness) { - u32 brightness = scale_input_to_fw(min, max, *user_brightness); + u32 brightness = scale_input_to_fw(max, *user_brightness); u8 lower_signal, upper_signal, upper_lum, lower_lum, lum; int left, right;
Is this still needed with "drm/amd/display: Fix backlight max_brightness to match exported range" https://github.com/torvalds/linux/commit/f1b5d8f9cc54ae8a2567ac126867ae488e1bf625
