`radeontool light off` does not turn off backlight

[Alex Deucher]

On Fri, Feb 10, 2012 at 12:09 PM, Paul Menzel
<paulepanter at users.sourceforge.net> wrote:
> Am Freitag, den 10.02.2012, 05:58 -0500 schrieb David Airlie:
>
>> > using radeontool 1.6.2-1.1 from Debian Wheezy/testing [1]
>> >
>> >         $ sudo radeontool --debug light off
>> >         Found card 1002:9555 (30000)
>> >         Radeon found. Base control address is 7f0746826000; base
>> >         framebuffer address is 7f0735e73000.
>> >         reading RADEON_LVDS_GEN_CNTL (2d0) is 00000000
>> >         writing RADEON_LVDS_GEN_CNTL (2d0) -> 00000000
>> >
>> > does not turn off the backlight of the laptop monitor. This is a
>> > Lenovo
>> > G555 laptop with a ATI Radeon HD 4200 graphic device [2].
>> >
>> > Do I need to submit a report to Freedesktop.org’s Bugzilla bug
>> > tracking system?
>>
>> radeontool doesn't support turning on/off backlights on newer GPUs, and I'm not sure I see any reason for it to do so.
>
> Because it says so in its description.
>
>> It was originally in radeontool as a hack around lack of drivers.
>
> Interesting. Maybe add to the `--help` text and the manual page which
> GPUs are supported.

radeontool should only be used for driver debugging.  Using radeontool
goes behind the driver's back and touches registers directly.  The
driver supports display dpms just fine.  If you are having a dpms
issue, please file a bug.

Alex