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

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Date:	Tue, 3 Feb 2009 09:53:08 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jesse.barnes@...el.com>,
	Andreas Schwab <schwab@...e.de>, Len Brown <lenb@...nel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: PCI PM: Restore standard config registers of all devices early



On Tue, 3 Feb 2009, Rafael J. Wysocki wrote:
> 
> As I said, I tend to prefer the "loop of disable_irq()" approach, because it
> would allow us to preserve the current ordering of ACPI operations.  Namely,
> if we do:
> 
> suspend devices (normal suspend)
>   loop of disable_irq()
>     late suspend of devices
>       _PTS
>         disable nonboot CPUs
>           local_irq_disable()
>             sysdev suspend
>               enter sleep state
>               get control from the BIOS
>             sysdev resume
>             (*)
>           local_irq_enable()
>         enable nonboot CPUs
>       _WAK
>     early resume of devices
>   loop of enable_irq()
> resume devices (normal resume)
> 
> the ordering of _PTS with respect to putting devices into low power states and
> disabling the nonboot CPUs will be the same as it is now and the same applies
> to _WAK and putting devices into D0 etc. (I really _really_ wouldn't like to
> change this ordering, since this alone is likely to break things badly).

Yes.

Also, make the "loop of disable/enable_irq()" phase be a helper function 
that also sets system_state to SYSTEM_SUSPENDING/SYSTEM_RUNNING 
respectively, and it should all be pretty clean, and the changes really 
should be pretty minimal.

> Now, there's one subtle problem with resume in this picture.  Namely, before
> running the "early resume of devices" we have to make sure that the interrupts
> will be masked.  However, masking MSI-X, for example, means writing into
> the memory space of the device, so we can't do it at this point.

I really don't think it matters. Why? We simply don't care.

All MSI-X things will still have to go through the regular irq layer, so 
the disable/enable_irq part, so even though we've done the 
"local_irq_enable()", we just don't care.

		Linus 
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