Re: [PATCH v2 1/3] PCI / ACPI: Use cached ACPI device state to get PCI device power state

Mika Westerberg
2019-06-25T10:08:56Z

On Tue, Jun 25, 2019 at 12:00:57PM +0200, Rafael J. Wysocki wrote:
> On Tue, Jun 25, 2019 at 11:46 AM Mika Westerberg
> <mika.westerberg@linux.intel.com> wrote:
> >
> > On Mon, Jun 24, 2019 at 01:14:47PM +0200, Rafael J. Wysocki wrote:
> > > > The problem here is that acpi_device_get_power() really only should be
> > > > used for two purposes: (1) To initialize adev->power.state, or to
> > > > update it via acpi_device_update_power(), and (2) by the
> > > > "real_power_state" sysfs attribute (of ACPI device objects). The
> > > > adev->power.state value should be used anywhere else, in principle, so
> > > > the Mika's patch is correct.
> > >
> > > Well, it is an improvement, but it is not sufficient.
> > >
> > > > [Note that adev->power.state cannot be updated after calling
> > > > acpi_device_get_power() to the value returned by it without updating
> > > > the reference counters of the power resources that are "on" *exactly*
> > > > because of the problem at hand here.]
> > >
> > > That is obviously correct, but ->
> > >
> > > > > but that's just an idle thought, not a suggestion.
> > > >
> > > > After the initialization of the ACPI subsystem, the authoritative
> > > > source of the ACPI device power state information is
> > > > adev->power.state. The ACPI subsystem is expected to update this
> > > > value as needed going forward (including system-wide transitions like
> > > > resume from S3).
> > >
> > > -> the "resume from S3 or hibernation" case needs special handling, because
> > > in that case the device power state need not reflect the information the ACPI
> > > subsystem has. That only matters if adev->power.state is ACPI_STATE_D0 and
> > > the device is actually *not* in D0, because in that case acpi_device_set_power()
> > > will not work.
> >
> > I guess you are talking about the special-cased devices that we leave in
> > D0 when system suspend (via firmware) is entered?
> >
> > > So that case is not covered currently (it should be rare in practice,
> > > though, if it happens at all), so something like the patch below (untested) may
> > > be needed in addition to the Mika's patch.
> >
> > Looks good to me.
>
> I actually decided to address this issue in acpi_device_set_power() as
> it may affect devices beyond PCI in principle. I will send a patch
> for that shortly.

Thanks!

> > > Still, there is also the "power state not matching" case in pci_pm_complete() that's
> > > need to be covered and the non-PCI ACPI PM has a similar issue in theory, so I
> > > need to think about this a bit more.
> >
> > Do you want me to hold off sending an updated version of the patch
> > series while we figure this one out or is it fine if I send it out now
> > and we can add further details on top?
>
> It is independent of the other fix, so it can be sent now just fine IMO.

OK, I'll send it out in a minute.