Re: [PATCH] PCI: Add pci shutdown ability

Pavel Machek
2005-04-26T20:23:53Z

Hi!

> > Well, you can do "half suspend to ram; change your frequency; half
> > resume" today, and it should work, but I do not think you'll like the
> > speed.
>
> Indeed. With people running things like cpuspeed daemons to dynamically
> scale speed, this is going to be really painful.
> Of course, any operation where we have to quiesce DMA is going to mean
> we're increasing latency around the scaling operation, but we don't
> have to go through all the hoops that are necessary when suspending.

> Thankfully some of the more recent implementations of speed/voltage
> scaling don't have this requirement.

Good, because some devices really need DMA. (Won't audio skip, and USB
break when you disable DMA? I do not see how cpufreq doing DMA disable
can be usefull.)

> > In a ideal world, calling device_suspend(PMSG_FREEZE) gets you exactly
> > that, and we'll do our best to make it fast enough.
> >
> > OTOH it *needs* to switch consoles to text one (because X may be
> > running DMA, right?); I do not think you'll like that one.
>
> That would be insane, and make cpufreq totally useless for anyone
> running X, so no. This is one of the reasons the kernel needs to
> arbitrate DMA on behalf of X. It just needs someone to do the work.

Yes... But it also looks like a lot of work :-(.
Pavel
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