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

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Message-Id: <200902030115.32659.rjw@sisk.pl>
Date:	Tue, 3 Feb 2009 01:15:31 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 Tuesday 03 February 2009, Linus Torvalds wrote:
> 
> On Tue, 3 Feb 2009, Rafael J. Wysocki wrote:
> > 
> > So, perhaps we can just loop over the interrupt links and disable them all
> > at this point?
> 
> Well, we could, but I think it's actually inferior. Why? Because timer 
> interrupts can come over those too.
> 
> So we're really better off just looping over our own software irq_desc 
> arrays. That has the feature that 
> 
>  (a) we can easily mark the individual irqs if we want to - in ways that 
>      we can never do if we end up looping over some hardware concept like 
>      the IO-APIC inputs. 
> 
>      IOW, we can easily add a magic flag for registering a timer 
>      interrupt (in fact, I guess we already have IRQF_TIMER), but we can 
>      also expand on this in the future with other purely software 
>      interrupt flags - ie a driver that knows it is irq-safe could just 
>      tell us so, and we wouldn't need to disable that irq if there are 
>      only irq-safe drivers registered on it.
> 
>  (b) it's portable, and handles re-sending the interrupts correctly 
>      (unlike just turning the interrupts off), and doesn't have any issues 
>      with worrying about polarity etc complicating issues.
> 
>      Looping over the irq links is really quite hard. Sure, we can do the 
>      ACPI thing, but that's platform-specific, _and_ it's not actually 
>      guaranteed to hit everything anyway (ie it likely only disables the 
>      mapped ones, not necessarily at all directly connected ones - IDE 
>      and USB tend to be direct irq's because they are often on the same 
>      chip as the irq controller).

OK

> > > @@ -1419,7 +1419,7 @@ int pci_restore_standard_config(struct pci_dev *dev)
> > > -	dev->current_state = PCI_D0;
> > > +	pci_update_current_state(dev, PCI_D0);
> > 
> > Good idea anyway.
> 
> Yeah, it probably makes sense to do this regardless of any PPC issues. 
> Exactly because we don't call the platform code.

OK, I'll send a (yet another) patch to Jesse for that.
 
> > Or perhaps put
> > 
> > current_state = PCI_UNKNOWN;
> > 
> > under that 'if (machine_is(powermac))' ?
> 
> Yes. That would be ok, but in _theory_ ACPI could hit the same thing, and 
> then the pci_restore_standard_config() really needs to do that anyway.

OK

BTW, on the PMAC the problematic driver appears to be the radeon driver,
according to Ben, and the breakage is not related to USB.

Thanks,
Rafael
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