Re: [PATCH v1 2/2] drm/amd/display: Adjust AUX brightness to be a granularity of 100

[Antheas Kapenekakis <lkml@antheas.dev>]

On Sun, 24 Aug 2025 at 10:54, Antheas Kapenekakis <lkml@antheas.dev> wrote:
>
> Certain OLED devices malfunction on specific brightness levels.
> Specifically, when DP_SOURCE_BACKLIGHT_LEVEL is written to with
> the minor byte being 0x00 and sometimes 0x01, the panel forcibly
> turns off until the device sleeps again. This is an issue on
> multiple handhelds, including OneXPlayer F1 Pro and Ayaneo 3
> (the panel is suspected to be the same-1080p 7in OLED).
>
> Below are some examples. This was found by iterating over brighness
> ranges while printing DP_SOURCE_BACKLIGHT_LEVEL. It was found that
> the screen would malfunction on specific values, and some of them
> were collected.
>
> Broken:
>  86016:  10101000000000000
>  86272:  10101000100000000
>  87808:  10101011100000000
> 251648: 111101011100000000
> 251649: 111101011100000001
>
> Working:
>  86144:  10101000010000000
>  87809:  10101011100000001
> 251650: 111101011100000010
>
> The reason for this is that the range manipulation is too granular.
> AUX is currently written to with a granularity of 1. Forcing 100,
> which on the Ayaneo 3 OLED yields 400*10=4000 values, is plenty of
> granularity and fixes this issue. Iterating over the values through
> Python shows that the final byte is never 0x00, and testing over the
> entire range with a cadence of 0.2s/it and 73 increments (to saturate
> the range) shows no issues. Windows likewise shows no issues.

Well Phil managed to fall into the value 332800, which has a 0 minor
bit. Unfortunate. In hindsight, every 256 hundreds there would be a
zero anyway.

Before I made this patch I made a partial refactor of panel-quirks
where a quirk like this could go to. But I would really prefer not to
do quirks. Ill send that too.

Antheas

> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3803
> Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 28 +++++++++++--------
>  1 file changed, 17 insertions(+), 11 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 cd0e2976e268..bb16adcafb88 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -4739,7 +4739,8 @@ static void amdgpu_dm_update_backlight_caps(struct amdgpu_display_manager *dm,
>  }
>
>  static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps,
> -                               unsigned int *min, unsigned int *max)
> +                               unsigned int *min, unsigned int *max,
> +                               unsigned int *multiple)
>  {
>         if (!caps)
>                 return 0;
> @@ -4748,10 +4749,12 @@ static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps,
>                 // Firmware limits are in nits, DC API wants millinits.
>                 *max = 1000 * caps->aux_max_input_signal;
>                 *min = 1000 * caps->aux_min_input_signal;
> +               *multiple = 100;
>         } else {
>                 // Firmware limits are 8-bit, PWM control is 16-bit.
>                 *max = 0x101 * caps->max_input_signal;
>                 *min = 0x101 * caps->min_input_signal;
> +               *multiple = 1;
>         }
>         return 1;
>  }
> @@ -4813,23 +4816,25 @@ static void convert_custom_brightness(const struct amdgpu_dm_backlight_caps *cap
>  static u32 convert_brightness_from_user(const struct amdgpu_dm_backlight_caps *caps,
>                                         uint32_t brightness)
>  {
> -       unsigned int min, max;
> +       unsigned int min, max, multiple;
>
> -       if (!get_brightness_range(caps, &min, &max))
> +       if (!get_brightness_range(caps, &min, &max, &multiple))
>                 return brightness;
>
>         convert_custom_brightness(caps, min, max, &brightness);
>
> -       // Rescale 0..max to min..max
> -       return min + DIV_ROUND_CLOSEST_ULL((u64)(max - min) * brightness, max);
> +       // Rescale 0..max to min..max rounding to nearest multiple
> +       return rounddown(
> +               min + DIV_ROUND_CLOSEST_ULL((u64)(max - min) * brightness, max),
> +               multiple);
>  }
>
>  static u32 convert_brightness_to_user(const struct amdgpu_dm_backlight_caps *caps,
>                                       uint32_t brightness)
>  {
> -       unsigned int min, max;
> +       unsigned int min, max, multiple;
>
> -       if (!get_brightness_range(caps, &min, &max))
> +       if (!get_brightness_range(caps, &min, &max, &multiple))
>                 return brightness;
>
>         if (brightness < min)
> @@ -4970,7 +4975,7 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
>         struct backlight_properties props = { 0 };
>         struct amdgpu_dm_backlight_caps *caps;
>         char bl_name[16];
> -       int min, max;
> +       int min, max, multiple;
>
>         if (aconnector->bl_idx == -1)
>                 return;
> @@ -4983,15 +4988,16 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
>         }
>
>         caps = &dm->backlight_caps[aconnector->bl_idx];
> -       if (get_brightness_range(caps, &min, &max)) {
> +       if (get_brightness_range(caps, &min, &max, &multiple)) {
>                 if (power_supply_is_system_supplied() > 0)
>                         props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->ac_level, 100);
>                 else
>                         props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->dc_level, 100);
>                 /* min is zero, so max needs to be adjusted */
>                 props.max_brightness = max - min;
> -               drm_dbg(drm, "Backlight caps: min: %d, max: %d, ac %d, dc %d\n", min, max,
> -                       caps->ac_level, caps->dc_level);
> +               drm_dbg(drm,
> +                       "Backlight caps: min: %d, max: %d, ac %d, dc %d, multiple: %d\n",
> +                       min, max, caps->ac_level, caps->dc_level, multiple);
>         } else
>                 props.brightness = props.max_brightness = MAX_BACKLIGHT_LEVEL;
>
> --
> 2.50.1
>
>