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

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Message-Id: <200812061822.35763.rjw@sisk.pl>
Date:	Sat, 6 Dec 2008 18:22:35 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Greg KH <greg@...ah.com>, Ingo Molnar <mingo@...e.hu>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Takashi Iwai <tiwai@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH 1/3] PCI: Rework default handling of suspend and resume

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?

OK

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.]

Rafael
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