From 6fd83a1c2cdea48c396f600795217fbdfb8124f6 Mon Sep 17 00:00:00 2001 From: Akhmed Zhitaev Date: Thu, 13 Aug 2026 22:09:59 +0500 Subject: [PATCH] drm/amd/display: Scale custom brightness curve from full range 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: stable@vger.kernel.org Signed-off-by: Akhmed Zhitaev Reviewed-by: Mario Limonciello (AMD) (Move to amdgpu_dm_backlight.c) Link: https://patch.msgid.link/20260813170959.22073-1-zhitaevakh@gmail.com Signed-off-by: Mario Limonciello Signed-off-by: Alex Deucher --- .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c index b66ca60e697d..e61bbc310f33 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c @@ -106,10 +106,10 @@ int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps, } EXPORT_IF_KUNIT(get_brightness_range); -/* 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] */ @@ -123,7 +123,7 @@ void convert_custom_brightness(const struct amdgpu_dm_backlight_caps *caps, 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;