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drm/amd/display: Scale custom brightness curve from full range

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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: 8dbd72cb79 ("drm/amd/display: Export full brightness range to userspace")
Cc: stable@vger.kernel.org
Signed-off-by: Akhmed Zhitaev <zhitaevakh@gmail.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
(Move to amdgpu_dm_backlight.c)
Link: https://patch.msgid.link/20260813170959.22073-1-zhitaevakh@gmail.com
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Akhmed Zhitaev 2026-08-13 22:09:59 +05:00 committed by Alex Deucher
parent 5827c7ad72
commit 6fd83a1c2c
1 changed files with 4 additions and 4 deletions
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8
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_backlight.c
View File

@ -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;