Re: [PATCH] PCI: Add pci shutdown ability

[Pavel Machek]

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
-- 
Boycott Kodak -- for their patent abuse against Java.
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