Re: [PATCH] drm/amd/display: Scale custom brightness curve from full range

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пт, 14 авг. 2026 г., 00:38 Mario Limonciello <[email protected]>:

>
>
> 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]>
>
> Thanks for this.
>
> We have moved the code in amd-staging-drm-next
>
>
> https://gitlab.freedesktop.org/agd5f/linux/-/commit/6c2b46e9774f13e45985f6da9f7d5f8458767b98
>
> As your changes are trivial, I'll adjust while commiting.
>
> Reviewed-by: Mario Limonciello (AMD) <[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;
> >
>
>