grub2 got strange power saving behavior (or is it my BIOS)

[Matthew Garrett]

On Sat, Mar 17, 2012 at 08:13:15PM +0000, Matthew Garrett wrote:
> On Sat, Mar 17, 2012 at 04:34:04PM +0200, Muayyad AlSadi wrote:
> 
> > is this just my BIOS or there is some sort of broken power management in grub2
> 
> Your BIOS.

I should probably elaborate on this. Backlight control is typically very 
hardware specific, with the exception of the ACPI backlight interface 
that's present on some hardware. To change the backlight, grub would 
either need to know how to drive your backlight hardware directly (which 
would be a lot of code) or contain an ACPI interpreter and switch your 
machine into ACPI mode. It doesn't do either, which means it can't be 
grub changing your backlight. It's pretty common for BIOSes to do that 
on their own - Fedora's kernel has to explicitly ask them to stop doing 
that in order to avoid it conflicting with the OS-level power 
management. That means it's almost certainly your BIOS doing it for you 
in grub.

-- 
Matthew Garrett | mjg59 at srcf.ucam.org