Re: wsdisplay brightness issue on amd64

On Mon, Aug 10, 2026 at 07:12:24AM +0100, Jason McIntyre wrote:
> On Mon, Aug 10, 2026 at 10:16:59AM +1000, Jonathan Gray wrote:
> > On Sun, Aug 09, 2026 at 08:44:45PM +0100, Jason McIntyre wrote:
> > > On Sun, Aug 09, 2026 at 11:12:56AM +0100, Jason McIntyre wrote:
> > > > hi/
> > > > 
> > > > when this machine boots, the screen display dims severely right about the
> > > > time my wsdisplay attach shows in dmesg. i can fix it manually by
> > > > adjusting display.brightness.
> > > > 
> > > > setting display.brightness to 0 is brighter than the booted default.
> > > > 
> > > > setting most display.brightness values work as normal, but 97-100 revert
> > > > it to this super dim state.
> > > > 
> > > > i have not updated the laptop in two weeks, so hard to pin down when
> > > > this would have happened (it's running current).
> > > > 
> > > > i confirmed this happened on a boot of stock /bsd.mp.
> > > > 
> > > > can;t think of anything else!
> > > > jmc
> > > > 
> > > 
> > > a little progress:
> > > 
> > > firstly i mis-diagnosed the issue. display.brightness=0 is not brighter
> > > than the booted default! i'm not exactly sure how i reached that
> > > conclusion.
> > > 
> > > but what i do see is values 97-100 severly dimming the screen. that
> > > suggests a weird round up/bounds check (heh, i'm winging it here). i
> > > noticed because i normally set max brightness in wsconsctl.conf, so it
> > > dimmed my screen.
> > > 
> > > i narrowed it down to a commit between
> > > 
> > > 	Sun Aug 2 23:29:09 MDT 2026
> > > and
> > > 	Mon Aug 3 22:42:09 MDT 2026
> > > 
> > > (thanks nick for the archive reminder)
> > > 
> > > commits on those dates suggest the updates to drm. there are a lot, and
> > > i'm blind. i'm ccing jsg in case he sees something obvious.
> > > 
> > > jmc
> > 
> > try this revert of 6.18.42's
> > drm/amd/display: Fix backlight max_brightness to match exported range
> > 
> 
> yes, the revert fixes it.

thanks, I've committed the revert