Henrique de Moraes Holschuh wrote:
> In fact, the "simple interfaces" for led and brightness control
> through sysfs are incomplete and a major pain in the ass.
Well, the glitch I'm seeing affects
/sys/class/backlight/thinkpad_screen/{actual_brightness,brightness} and
/proc/acpi/ibm/brightness identically. So whatever design issues the
former may have, that's not the root of the current problem.
> Eh? actual_brightness is changing but the *display* backlight level (not the
> value of any sysfs files, the actual screen brightness) is not changing?
Yes, that's exactly what's happening. Weird, isn't it?
> If that's happening, it is a bug in thinkpad_acpi. Try playing with the
> different brightness_mode settings, and please tell me which one worked
> properly.
To create the simplest test environment possible, I booted into
single-user mode. So no HAL, no X, nothing but the basics. My findings:
The brightness keys change the physical screen as expected at the GRUB
boot prompt.
The brightness keys change the value reported by actual_brightness but
do not actually change the physical screen once the machine is booted
and running Linux in single-user mode. I tried all four values (0-3) of
brightness_mode, and they all behave the same in this regard.
actual_brightness changes but the physical screen does not. Echoing my
own value into brightness works: it changes both actual_brightness and
the physical screen.
This is also what happens if the thinkpad_acpi module has been hidden
from view and therefore never loaded into the kernel at all. Of course
I cannot view actual_brightness in this case, but I can say that the
brightness keys have no affect on the actual brightness of the physical
screen.
Weird indeed. What should I try next?
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