[ltp] Thinkpad keyboard backlight ACPI interface

[Pali Rohár]

On Tuesday 28 July 2015 13:17:58 Bjørn Mork wrote:
> Pali Rohár <pali.rohar@gmail.com> writes:
> 
> > I would like to write kernel patch for thinkpad_acpi.c to support 
> > keyboard backlight (like other modules in drivers/platform/x86/ tree), 
> > but last missing information is how to detect current level of 
> > brightness and check if backlight is supported...
> 
> Based on the code you posted, I would assume that MLCG returns the
> current brightness level.  Did you test that?
> 

Of course and it returns:

0x50200 - off
0x50201 - level 1
0x50202 - level 2

But I do not understand why it returns 0x5020{0,1,2} and not only 0,1,2.

MLCS returns 0x0.

> The thinkpad_acpi driver use code like this to test for supported
> features:
> 
>       tp_features.bluetooth = hkey_handle && acpi_evalf(hkey_handle, &status, "GBDC", "qd");
> 
> You could do something similar for the keyboard backlight feature,
> couldn't you?
> 

Sounds good, but I do not know what "GBDC" and "qd" means... :-(
So because of that I need some "documentation" which say how to do it.

-- 
Pali Rohár
pali.rohar@gmail.com