Re: PCI PM: Restore standard config registers of all devices early

[Benjamin Herrenschmidt]

On Mon, 2009-02-02 at 12:41 -0800, Linus Torvalds wrote:
> 
> On Tue, 3 Feb 2009, Benjamin Herrenschmidt wrote:
> > 
> > I'd rather hook it up inside pci_set_power_state()...
> 
> Umm. But you already _have_ that. Look at platform_pci_set_power_state(). 
> It gets called before turning the device on (pci_raw_set_power_state(D0)) 
> and after turning the device off (pci_raw_set_power_state(D1+))
> 
> Maybe you missed it? It's how ACPI does things.

I may well have, it didn't exist when my stuff was written.

> However, the issue you see is that pci_restore_standard_config() doesn't 
> call it, because at least with ACPI, the ACPI code simply isn't ready to 
> be called with interrupts off. So it looks like you may be looking at the 
> wrong thing, hmm?

Well.. yes and no... I still don't see how it can be sane to whack config
space back before the device has been turned back on. I wouldn't be surprised
if some devices don't grok well their BARs being written while not in D0.

I suppose I can always add another hook inside pci_restore_blah for my specific
case but I can also very easily see that can of worms hitting even more badly
in tight embedded environments such as handhelds, who use things like fine clock
control a lot more extensively.

In fact, even on x86, I'm not sure it's kosher to restore the config space
before you called ACPI...

Ben.


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