Re: [PATCH AUTOSEL 4.14 086/105] PCI / ACPI: Use cached ACPI device state to get PCI device power state

[Sasha Levin]

On Tue, Jul 16, 2019 at 11:22:44AM +0200, Rafael J. Wysocki wrote:
> On 7/15/2019 4:28 PM, Sasha Levin wrote:
> > From: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> >
> > [ Upstream commit 83a16e3f6d70da99896c7a2639c0b60fff13afb8 ]
> >
> > The ACPI power state returned by acpi_device_get_power() may depend on
> > the configuration of ACPI power resources in the system which may change
> > any time after acpi_device_get_power() has returned, unless the
> > reference counters of the ACPI power resources in question are set to
> > prevent that from happening. Thus it is invalid to use acpi_device_get_power()
> > in acpi_pci_get_power_state() the way it is done now and the value of
> > the ->power.state field in the corresponding struct acpi_device objects
> > (which reflects the ACPI power resources reference counting, among other
> > things) should be used instead.
> >
> > As an example where this becomes an issue is Intel Ice Lake where the
> > Thunderbolt controller (NHI), two PCIe root ports (RP0 and RP1) and xHCI
> > all share the same power resources. The following picture with power
> > resources marked with [] shows the topology:
> >
> >   Host bridge
> >     |
> >     +- RP0 ---\
> >     +- RP1 ---|--+--> [TBT]
> >     +- NHI --/   |
> >     |            |
> >     |            v
> >     +- xHCI --> [D3C]
> >
> > Here TBT and D3C are the shared ACPI power resources. ACPI _PR3() method
> > of the devices in question returns either TBT or D3C or both.
> >
> > Say we runtime suspend first the root ports RP0 and RP1, then NHI. Now
> > since the TBT power resource is still on when the root ports are runtime
> > suspended their dev->current_state is set to D3hot. When NHI is runtime
> > suspended TBT is finally turned off but state of the root ports remain
> > to be D3hot. Now when the xHCI is runtime suspended D3C gets also turned
> > off. PCI core thus has power states of these devices cached in their
> > dev->current_state as follows:
> >
> >   RP0 -> D3hot
> >   RP1 -> D3hot
> >   NHI -> D3cold
> >   xHCI -> D3cold
> >
> > If the user now runs lspci for instance, the result is all 1's like in
> > the below output (00:07.0 is the first root port, RP0):
> >
> > 00:07.0 PCI bridge: Intel Corporation Device 8a1d (rev ff) (prog-if ff)
> >     !!! Unknown header type 7f
> >     Kernel driver in use: pcieport
> >
> > In short the hardware state is not in sync with the software state
> > anymore. The exact same thing happens with the PME polling thread which
> > ends up bringing the root ports back into D0 after they are runtime
> > suspended.
> >
> > For this reason, modify acpi_pci_get_power_state() so that it uses the
> > ACPI device power state that was cached by the ACPI core. This makes the
> > PCI device power state match the ACPI device power state regardless of
> > state of the shared power resources which may still be on at this point.
> >
> > Link: https://lore.kernel.org/r/20190618161858.77834-2-mika.westerberg@xxxxxxxxxxxxxxx
> > Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  drivers/pci/pci-acpi.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> > index a3cedf8de863..688e195e85b4 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -563,7 +563,8 @@ static pci_power_t acpi_pci_get_power_state(struct pci_dev *dev)
> >  	if (!adev || !acpi_device_power_manageable(adev))
> >  		return PCI_UNKNOWN;
> > -	if (acpi_device_get_power(adev, &state) || state == ACPI_STATE_UNKNOWN)
> > +	state = adev->power.state;
> > +	if (state == ACPI_STATE_UNKNOWN)
> >  		return PCI_UNKNOWN;
> >  	return state_conv[state];
>
> This requires additional changes to really work in all cases, please 
> do not include it alone into -stable.

I've dropped it, thanks!

--
Thanks,
Sasha