Re: [PATCH] PCI/PM: Put devices to low power state on shutdown

[Mario Limonciello]

On 9/11/2024 14:16, Mario Limonciello wrote:
> On 9/11/2024 14:05, Bjorn Helgaas wrote:
> > On Fri, Jul 12, 2024 at 02:24:11PM +0800, Kai-Heng Feng wrote:
> > > Some laptops wake up after poweroff when HP Thunderbolt Dock G4 is
> > > connected.
> > >
> > > The following error message can be found during shutdown:
> > > pcieport 0000:00:1d.0: AER: Correctable error message received from 
> > > 0000:09:04.0
> > > pcieport 0000:09:04.0: PCIe Bus Error: severity=Correctable, 
> > > type=Data Link Layer, (Receiver ID)
> > > pcieport 0000:09:04.0:   device [8086:0b26] error 
> > > status/mask=00000080/00002000
> > > pcieport 0000:09:04.0:    [ 7] BadDLLP
> > >
> > > Calling aer_remove() during shutdown can quiesce the error message,
> > > however the spurious wakeup still happens.
> > >
> > > The issue won't happen if the device is in D3 before system shutdown, so
> > > putting device to low power state before shutdown to solve the issue.
> > >
> > > I don't have a sniffer so this is purely guesswork, however I believe
> > > putting device to low power state it's the right thing to do.
> >
> > My objection here is that we don't have an explanation of why this
> > should matter or a pointer to any spec language about this situation,
> > so it feels a little bit random.
> >
> > I suppose the problem wouldn't happen if AER interrupts were disabled?
> > We already do disable them in aer_suspend(), but maybe that's not used
> > in the shutdown path?
> >
> > My understanding is that .shutdown() should turn off device interrupts
> > and stop DMA.  So maybe we need an aer_shutdown() that disables
> > interrupts?
>
> IMO I see this commit as two problems with the same solution.
>
> I don't doubt that cleaning up AER interrupts in the shutdown path would 
> help AER messages, but you really don't "want" devices to be in D0 when 
> the system is "off" because even if the system is off some rails are 
> still active and the device might still be powered.
>
> A powered device could cause interrupts (IE a spurious wakeup).

It's a bit of a stretch, but ACPI 7.4.2.5 and 7.4.2.6 are the closest 
corollary to a spec I can find.

"Devices states are compatible with the current Power Resource states. 
In other words, all devices are in the D3 state when the system state is 
S4."

https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/07_Power_and_Performance_Mgmt/oem-supplied-system-level-control-methods.html

> > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=219036
> > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> > > ---
> > >   drivers/pci/pci-driver.c | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > > index af2996d0d17f..4c6f66f3eb54 100644
> > > --- a/drivers/pci/pci-driver.c
> > > +++ b/drivers/pci/pci-driver.c
> > > @@ -510,6 +510,14 @@ static void pci_device_shutdown(struct device *dev)
> > >       if (drv && drv->shutdown)
> > >           drv->shutdown(pci_dev);
> > > +    /*
> > > +     * If driver already changed device's power state, it can mean the
> > > +     * wakeup setting is in place, or a workaround is used. Hence 
> > > keep it
> > > +     * as is.
> > > +     */
> > > +    if (!kexec_in_progress && pci_dev->current_state == PCI_D0)
> > > +        pci_prepare_to_sleep(pci_dev);
> > > +
> > >       /*
> > >        * If this is a kexec reboot, turn off Bus Master bit on the
> > >        * device to tell it to not continue to do DMA. Don't touch
> > > --
> > > 2.43.0