linux-kernel - Re: [PATCH] PCI / PM: Fix fallback to PCI_D0 in pci_platform_power

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Date:	Tue, 16 Apr 2013 12:31:55 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	"Benenati, Chris J" <chris.j.benenati@...el.com>,
	Ajaykumar Hotchandani <ajaykumar.hotchandani@...cle.com>
Subject: Re: [PATCH] PCI / PM: Fix fallback to PCI_D0 in pci_platform_power_transition()

On Tue, Apr 16, 2013 at 12:01 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Monday, April 15, 2013 02:18:18 PM Bjorn Helgaas wrote:
>> On Fri, Apr 12, 2013 at 11:50 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> > On Fri, Apr 12, 2013 at 4:58 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> >> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> >>
>> >> Commit b51306c (PCI: Set device power state to PCI_D0 for device
>> >> without native PM support) modified pci_platform_power_transition()
>> >> by adding code causing dev->current_state for devices that don't
>> >> support native PCI PM but are power-manageable by the platform to be
>> >> changed to PCI_D0 regardless of the value returned by the preceding
>> >> platform_pci_set_power_state().  In particular, that also is done
>> >> if the platform_pci_set_power_state() has been successful, which
>> >> causes the correct power state of the device set by
>> >> pci_update_current_state() in that case to be overwritten by PCI_D0.
>> >>
>> >> Fix that mistake by making the fallback to PCI_D0 only happen if
>> >> the platform_pci_set_power_state() has returned an error.
>> >>
>> >> Reported-by: Chris J. Benenati <chris.j.benenati@...el.com>
>> >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> >> Cc: <stable@...r.kernel.org>
>>
>> I folded in Yinghai's simplification and added a URL to Chris's report
>> and applied to my pci/rafael-pm branch:
>> http://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/log/?h=pci/rafael-pm
>>
>> If it still looks good to you, Rafael, I'll merge it to next for v3.10.
>
> Well, the simplification adds an extra check for error into both code paths,
> so I'm not sure if it's really worth it (that's why I didn't do it originally
> in the first place), but I suppose that's not a big deal.  It looks good as far
> as the correctness is concerned anyway.
>
>> I don't know what the user-visible effect of this is, and it's been
>> around for a long time, but if you think this should go in v3.9
>> instead, let me know.
>
> I think v3.9+stable should be sufficient.

It sounds like you meant to say "v3.10+stable should be sufficient".
Is that right, or do you want me to push this to Linus before v3.9 is
released?

>> >> ---
>> >>  drivers/pci/pci.c |    3 +--
>> >>  1 file changed, 1 insertion(+), 2 deletions(-)
>> >>
>> >> Index: linux-pm/drivers/pci/pci.c
>> >> ===================================================================
>> >> --- linux-pm.orig/drivers/pci/pci.c
>> >> +++ linux-pm/drivers/pci/pci.c
>> >> @@ -646,8 +646,7 @@ static int pci_platform_power_transition
>> >>                 error = platform_pci_set_power_state(dev, state);
>> >>                 if (!error)
>> >>                         pci_update_current_state(dev, state);
>> >> -               /* Fall back to PCI_D0 if native PM is not supported */
>> >> -               if (!dev->pm_cap)
>> >> +               else if (!dev->pm_cap) /* Fall back to PCI_D0 */
>> >>                         dev->current_state = PCI_D0;
>> >>         } else {
>> >>                 error = -ENODEV;
>> >>
>> >
>> > Acked-by: Yinghai Lu <yinghai@...nel.org>
>> >
>> > also could simplify it further.
>> >
>> > ---
>> >  drivers/pci/pci.c |   12 ++++--------
>> >  1 file changed, 4 insertions(+), 8 deletions(-)
>> >
>> > Index: linux-2.6/drivers/pci/pci.c
>> > ===================================================================
>> > --- linux-2.6.orig/drivers/pci/pci.c
>> > +++ linux-2.6/drivers/pci/pci.c
>> > @@ -646,15 +646,11 @@ static int pci_platform_power_transition
>> >          error = platform_pci_set_power_state(dev, state);
>> >          if (!error)
>> >              pci_update_current_state(dev, state);
>> > -        /* Fall back to PCI_D0 if native PM is not supported */
>> > -        if (!dev->pm_cap)
>> > -            dev->current_state = PCI_D0;
>> > -    } else {
>> > +    } else
>> >          error = -ENODEV;
>> > -        /* Fall back to PCI_D0 if native PM is not supported */
>> > -        if (!dev->pm_cap)
>> > -            dev->current_state = PCI_D0;
>> > -    }
>> > +
>> > +    if (error && !dev->pm_cap) /* Fall back to PCI_D0 */
>> > +        dev->current_state = PCI_D0;
>> >
>> >      return error;
>> >  }
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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