[linux-pm] Re: [RFC] powermac: proper sleep management

[Alan Stern]

On Tue, 13 Nov 2007, Benjamin Herrenschmidt wrote:

> 
> On Mon, 2007-11-12 at 17:32 +0100, Johannes Berg wrote:
> > > Looks good to me, +/- a couple of things:
> > > 
> > >  - We _REALLY_ want the freezer to be optional and not enabled by
> > > default on PowerPC. Maybe make it a compile option ?
> > 
> > Well, Alan is going to tell you that USB will break. If we need
> > confirmation for that I can do the test he suggested to you or Paul a
> > while ago.
> 
> Then USB is broken today on powermacs and need to be fixed. We had a
> clear agreement at KS this year that the freezer was at best a band-aid
> and that drivers -had- to be fixed to cope regardless.

More accurately, freezing user tasks is at best a band-aid.  However 
some kernel threads do need to be frozen, and keeping the freezer 
around for their use makes sense.  It has less overhead -- I think 
-- than adding new code to do the freezing in each of these threads.

(It's true that USB drivers in general aren't written to operate in a
freezerless system-suspend environment.  That's a harder problem and
it will have to be fixed driver-by-driver, over time.  The same may be
true for lots of non-USB char device drivers as well.  Pick your 
favorite char device driver: How will it behave if a user task submits 
an I/O request after the device has been suspended?)

Alan Stern