Re: [PATCH 1/3] PCI: Rework default handling of suspend and resume

From: Rafael J. Wysocki
Date: Sat Dec 06 2008 - 12:23:45 EST

On Saturday, 6 of December 2008, Linus Torvalds wrote:
> On Sat, 6 Dec 2008, Rafael J. Wysocki wrote:
> >
> > Rework the handling of suspend and resume of PCI devices which have
> > no drivers or the drivers of which do not provide any suspend-resume
> > callbacks in such a way that their standard PCI configuration
> > registers will be saved and restored with interrupts disabled.
> Ok, I think this is good, but I _also_ think that we should do one more
> fix:
> - if a device uses the new-format suspend/resume structure, we should do
> the low-level save-restore _unconditionally_ in the PCI layer.
> Because apparently there is only a single user of the new format, and that
> single user got it wrong. So wouldn't it be much nicer to just _remove_
> the code from the USB host controllers that does the save/restore thing.

USB doesn't use that for PCI suspend-resume, it uses it for suspend-resume of
USB devices behind the controller.

> Quite frankly, the USB code really does look wrong. Not just in that it
> enables the BAR's before restoring them, but on the suspend side it
> actually puts the device into D3_hot _before_ it then does the whole
> "pci_enable_wake()", which I'm not at all sure will necessarily work. I'm
> pretty sure that you should enable wakeup events _before_ going to sleep.

Yeah. Or simply use pci_prepare_to_sleep() and be done with it.

> If the generic PCI layer unconditionally did the suspend as the last thing
> it does (and the resume as the first thing), then drivers couldn't do
> insane things like that, even by mistake.
> Hmm?


But then we will save the device's registers in the "sleeping" state. Is this
going to be entirely correct in all possible cases? [pci_save_state() doesn't
save the PM registers, so that _should_ be correct, but I don't have _that_
much experience with these things.]

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