Fwd: Linux On A Toshiba Click Mini...

[Nicolas Huillard]

Le jeudi 10 mars 2016 à 13:26 +0100, Gee a écrit :
> On 03/10/2016 01:11 PM, Paul Mansfield wrote:
> > On 10 March 2016 at 06:53,  <christian at boltares.de> wrote:
> >> Hi,
> >>
> >> as a temporary solution to the backlight problem you can use
> >>
> >> xrandr --output UNKNOWN1 --brightness 0.5
> > 
> > that's interesting, it suggests that the driver knows how to control
> > the backlight, we just need to find a way of linking the control with
> > the user space tools.
> > 
> 
> As a cautionary note, I believe that xrandr doesn't actually control
> screen brightness on a hardware level. I jsut tested this on my current
> machine, where I adjust brightness with xbacklight. Even if I reduce
> brightness, xrandr still claims that brightness is at 1.0. I think I
> also saw some forum posts to this effect.
> 
> So, if you're just concerned with the screen being too bright the xrandr
> workaround is useful, but I suspect it's not going to improve battery
> life (I'd be interested to hear if that can be disproved of course, but
> atm that's probably hard to test directly on our Click Mini as we don't
> have battery indication).

What I read from the kernel logs at boot time, is that brightness
control doesn't work because the PWM driving the LEDs is not available
(some kind of BIOS misconfiguration or wrong use, to be fixed at kernel
level).

xrandr just tweaks the pixel outputs, ie. grey instead of white :
--brightness brightness
        Multiply the gamma values on the crtc currently attached to the
        output to specified floating value. Useful for overly bright or
        overly dim outputs. However, this is a software only
        modification, if your hardware has support to actually change
        the brightness, you will probably prefer to use xbacklight.

xbacklight will hopefully use the actual LED hardware, and will probably
fail to adjust it, thanks to the PWM initialisation error.

HTH

-- 
Nicolas Huillard
nicolas at huillard.net
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