Re: [REGRESSION] [PATCH] drm/amd/display: fix initial backlight brightness calculation

On 7/20/25 4:36 AM, Lauri Tirkkonen wrote:

DIV_ROUND_CLOSEST(x, 100) returns either 0 or 1 if 0<x<=100, so the division needs to be performed after the multiplication and not the other way around, to properly scale the value.

Fixes: 6c56c8ec6f97 ("drm/amd/display: Fix default DC and AC levels") Signed-off-by: Lauri Tirkkonen lauri@hacktheplanet.fi

---

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 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 f58fa5da7fe5..8a5b5dfad1ab 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -4941,9 +4941,9 @@ 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 (power_supply_is_system_supplied() > 0)

• 	props.brightness = (max - min) * DIV_ROUND_CLOSEST(caps->ac_level, 100);
  

• 	props.brightness = DIV_ROUND_CLOSEST((max - min) * caps->ac_level, 100);
  

  else

• 	props.brightness = (max - min) * DIV_ROUND_CLOSEST(caps->dc_level, 100);
  

• 	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,

Thanks! The change makes sense. Besides Greg's comments can you please send out of the regression thread? IMO This should be it's own patch thread.