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SubjectRe: [PATCH] Longhaul - call suspend(PMSG_FREEZE) before and resume() after

> I posted this to Dave Jones, but:
> > This really should also get posted to linux-kernel, though I don't
> > think people are going to be particularly enthusiastic about exposing
> > these innards to modules.
> So I'm posting this patch here too. I'm not subscribed to this list.
> If You wish email me.
> Minor change: preempt_disabled() goto_sleep_pci() and wakeup_pci()
> causes "sheduling while atomic". So in this patch below it isn't
> preempt_disabled(). But I think that this should be protected
> in some way.

Well, suspend/resume is normally called during system suspend/resume,
so it has 'interesting' locking requirements.

> How it works:
> 1. Call suspend(PMSG_FREEZE) for each block device.
> 2. Call suspend(PMSG_FREEZE) for each PCI device.
> 3. Change CPU frequency.
> 4. Call resume() for each PCI device.
> 5. Call resume() for each block device.
> Result: No more broken DMA transfers caused by frequency change.

Result: system hang if userspace tries to do request at the same time
-- PCI drivers probably were not designed for _that_... but we
probably want to fix them, anyway, so this is probably ok (but expect
to do some driver debugging).

But you should really add that preempt_disable and not try this on smp

Thanks for all the (sleeping) penguins.
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