[Bug 31920] New: Brightness control is erratic (/sys/class/backlight/nv_backlight/max_brightness is wrong)

[bugzilla-daemon-CC+yJ3UmIYqDUpFQwHEjaQ@public.gmane.org]

https://bugs.freedesktop.org/show_bug.cgi?id=31920

           Summary: Brightness control is erratic
                    (/sys/class/backlight/nv_backlight/max_brightness is
                    wrong)
           Product: xorg
           Version: git
          Platform: Other
        OS/Version: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/nouveau
        AssignedTo: nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
        ReportedBy: rohandhruva-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
         QAContact: xorg-team-go0+a7rfsptAfugRpC6u6w@public.gmane.org


I have a Sony Vaio CW2 laptop, with an Nvidia GeForce 310M card. I am using the
nouveau driver from git (via the xorg-edgers ubuntu repository). I have to say
it works really well - I even get desktop effects in KDE with Gallium. 

However, there is one problem with screen brightness. The max_brightness value
for the backlight interface (/sys/class/backlight/nv_backlight/max_brightness)
is set to 1025. When I use KDE power-devil (or any brightness control tool), it
reduces the brightness by tiny fractions, which still keeps the screen at full
brightness. The brightness actually varies only between 0 and 127 (128-1025 are
full brightness), and then too only if I change it in increments of 10 or 20. I
think ideally the max_brightness value should be 7 (or 10?) and it should vary
in steps of 1.

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