Re: Re: [RFC] powermac: proper sleep management

Alan Stern
2007-11-12T20:40:58Z

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