Integrating OS power management with the X server

[Egbert Eich]

Keith Packard writes:
 > 
 > Around 10 o'clock on Oct 25, Nate Lawson wrote:
 > 
 > > I'd like more information as to what the X server actually does with this
 > > event.
 > 
 > To ensure a reasonable chance of recovery, the X server switches back to 
 > whatever mode the video card started in.  To allow the video card to be 
 > powered down, it also pulls all data out of the card back into memory.
 > 
 > As the OS has no idea what the X server has done, there's really no 
 > substitute for having the X server know what's going on.
 > 
 > > Is there any situation where it actually needs to veto a suspend?  
 > 
 > I can't think of any.

It does not veto but it delays the suspend until it is has done all
preparations.

 > 
 > > Does it potentially take seconds to save state?
 > 
 > Yes.  It has to pull all data out of the video card and potentially run 
 > the BIOS to get back to text mode.

Effectively it does the same as when doing a VT switch. Saving state is
actually not so bad as we don't save static register states as we have
calculated them when calculating the video mode.

 > 
 > > Does it need to access other running subsystems or is it self-contained?
 > 
 > Hmm.  I don't think so.

Its self contained. It interfaces to a kernel device.

Egbert.