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

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Date:	Tue, 3 Feb 2009 07:48:20 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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, Benjamin Herrenschmidt wrote:
> 
> Now where it gets funny is that I've added code to read the BAR and
> command register content before, between, and after those calls and
> print it and .. they are sane... Until i discovered that what happens is
> that the new generic code seems to actually blast 0 all over my config
> space if I don't call pci_save_state() in suspend(). I suppose I was
> missing a "mandatory" call here... but the core should be more robust,
> ie it shouldn't erase the config space of something because a driver
> "forgot" to call pci_save_state() !

You've found a bug somewhere.

We _should_ be saving things, the legacy code does something like this:

        if (drv && drv->suspend) {
                pci_dev->state_saved = false;

                i = drv->suspend(pci_dev, state);
                suspend_report_result(drv->suspend, i);
                if (i)
                        return i;

                if (pci_dev->state_saved)
                        goto Fixup;

                if (WARN_ON_ONCE(pci_dev->current_state != PCI_D0))
                        goto Fixup;
        }

        pci_save_state(pci_dev);

ie if your ->suspend function doesn't use pci_save_state() itself (which 
sets that "state_saved" flag to true), then the generic code will do it 
for you.

Also, on the resume path, we actually have

        if (pci_dev->state_saved)
                pci_restore_standard_config(pci_dev);

so I wonder how the heck you got that blast of all zeroes - because we 
clearly shouldn't be trying to restore any unsaved state!

So if you can figure out how it does all that...

		Linus
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