Re: Could not change brightness anymore with i915kms & acpi_video modules c 202211

On 1/31/23 13:33, Poul-Henning Kamp wrote:
 > Speaking of backlight(8):  On my T14s, I see the following:
 >
 > If I set the light with backlight(8) to something, say 30%, and then
 > change the power-situation, for instance by unplugging the charger,
 > the backlight goes up to 100%.
 >
 > If I then try to set it back to 30% with backlight(8), nothing happens.
 >
 > If I use any other value, for instance 31%, backlight(8) does the job.
 >
 > I guess somewhere some code says "It's always 30%, just return" ?
 >
 > This might be a bit confusing if you have the intensity encoded in
 > some script, which then "sometimes does not work"...
 >
Actually, I think the problem is a bit deeper, as yet-to-come version of 
DRM 5.14 suffers from the similar problem: 
https://github.com/freebsd/drm-kmod/pull/226#issuecomment-1400399357. 
TL;DR: new DRM code sets brightness to 0% while backlight(8) reports 100%.

Regards,
meka