Re: [PATCH AUTOSEL 4.14 15/31] PCI: PM: Avoid possible suspend-to-idle issue

[Sasha Levin]

On Tue, Jun 11, 2019 at 05:25:48PM +0200, Rafael J. Wysocki wrote:
> On 6/8/2019 1:46 PM, Sasha Levin wrote:
> > From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
> >
> > [ Upstream commit d491f2b75237ef37d8867830ab7fad8d9659e853 ]
> >
> > If a PCI driver leaves the device handled by it in D0 and calls
> > pci_save_state() on the device in its ->suspend() or ->suspend_late()
> > callback, it can expect the device to stay in D0 over the whole
> > s2idle cycle.  However, that may not be the case if there is a
> > spurious wakeup while the system is suspended, because in that case
> > pci_pm_suspend_noirq() will run again after pci_pm_resume_noirq()
> > which calls pci_restore_state(), via pci_pm_default_resume_early(),
> > so state_saved is cleared and the second iteration of
> > pci_pm_suspend_noirq() will invoke pci_prepare_to_sleep() which
> > may change the power state of the device.
> >
> > To avoid that, add a new internal flag, skip_bus_pm, that will be set
> > by pci_pm_suspend_noirq() when it runs for the first time during the
> > given system suspend-resume cycle if the state of the device has
> > been saved already and the device is still in D0.  Setting that flag
> > will cause the next iterations of pci_pm_suspend_noirq() to set
> > state_saved for pci_pm_resume_noirq(), so that it always restores the
> > device state from the originally saved data, and avoid calling
> > pci_prepare_to_sleep() for the device.
> >
> > Fixes: 33e4f80ee69b ("ACPI / PM: Ignore spurious SCI wakeups from suspend-to-idle")
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Reviewed-by: Keith Busch <keith.busch@xxxxxxxxx>
> > Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  drivers/pci/pci-driver.c | 17 ++++++++++++++++-
> >  include/linux/pci.h      |  1 +
> >  2 files changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > index ea69b4dbab66..f5d66335fe53 100644
> > --- a/drivers/pci/pci-driver.c
> > +++ b/drivers/pci/pci-driver.c
> > @@ -726,6 +726,8 @@ static int pci_pm_suspend(struct device *dev)
> >  	struct pci_dev *pci_dev = to_pci_dev(dev);
> >  	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> > +	pci_dev->skip_bus_pm = false;
> > +
> >  	if (pci_has_legacy_pm_support(pci_dev))
> >  		return pci_legacy_suspend(dev, PMSG_SUSPEND);
> > @@ -799,7 +801,20 @@ static int pci_pm_suspend_noirq(struct device *dev)
> >  		}
> >  	}
> > -	if (!pci_dev->state_saved) {
> > +	if (pci_dev->skip_bus_pm) {
> > +		/*
> > +		 * The function is running for the second time in a row without
> > +		 * going through full resume, which is possible only during
> > +		 * suspend-to-idle in a spurious wakeup case.  Moreover, the
> > +		 * device was originally left in D0, so its power state should
> > +		 * not be changed here and the device register values saved
> > +		 * originally should be restored on resume again.
> > +		 */
> > +		pci_dev->state_saved = true;
> > +	} else if (pci_dev->state_saved) {
> > +		if (pci_dev->current_state == PCI_D0)
> > +			pci_dev->skip_bus_pm = true;
> > +	} else {
> >  		pci_save_state(pci_dev);
> >  		if (pci_power_manageable(pci_dev))
> >  			pci_prepare_to_sleep(pci_dev);
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 59f4d10568c6..430f3c335446 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -346,6 +346,7 @@ struct pci_dev {
> >  						   D3cold, not set for devices
> >  						   powered on/off by the
> >  						   corresponding bridge */
> > +	unsigned int	skip_bus_pm:1;	/* Internal: Skip bus-level PM */
> >  	unsigned int	ignore_hotplug:1;	/* Ignore hotplug events */
> >  	unsigned int	hotplug_user_indicators:1; /* SlotCtl indicators
> >  						      controlled exclusively by
>
> This has been reported to be problematic, I wouldn't recommend taking 
> it for -stable at this point.

I've dropped it, thank you.

--
Thanks,
Sasha