On Thu, 2006-09-14 at 11:18 +0200, Pavel Machek wrote:
> On Tue, 2006-09-12 at 11:21 +0200, Pavel Machek wrote:
> >
> > > Ok, so what is needed is message to X "we are suspending", and X
> needs
> > > to respond "okay, I'm ready, no need for console switch".
> >
> > This presumes an external agent to X controlling the fast
> > suspend/resume, with messages having to flow to and from X, and to
> and
> > from the kernel, with the kernel in the middle.
> >
> > Another simpler option is X itself just telling the kernel to suspend
> > without console switch, as the handoff of the display to the DCON chip
> > has to be done with X and with an interrupt signaling completion of the
> > handoff. This would be triggered by an inactivity timeout in the X
> > server.
>
> Whoa... that's a hack.. but yes, you can probably do that, and I think
> kernel even has neccessary interfaces already. (They were needed for
> uswsusp).
Glad you like it ;-). Dunno which way we'll go yet, though it will get
to the top of the pile to implement this fall. I suspect we may go this
route to get going, but explore the more general solution as we get more
sophisticated power management policies and standards in place.
>
> > > Alternatively, hack kernel to take control from X without actually
> > > switching consoles. That should be possible even with current
> > > interface.
> >
> > This would require saving/restoring all graphics state in the kernel
> > (and X already has that state internally). Feasible, but seems like
>
> Hmm, save/restore graphics state from the kernel would of course be
> clean solution, but you should have that anyway... what if someone
> suspends without X running?
X knows its graphics state; it has to remember it all to know when it
has to be changed; on resume, resume can reinit the graphics state to
what the console wants/needs.
If you VT switch back to X, X can restore the graphics state to what it
remembers.
>
> And of course you can just cheat, and not do kernel save-state on your
> system.
Yup, though it isn't clear to me I'd call it cheating. In some ways,
what I just described to handle suspends when X is not running is really
robust and simple. And you don't have divided responsibility for
remembering the state. Simple == good in my book.
- Jim
--
Jim Gettys
One Laptop Per Child
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