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

[Kai-Heng Feng]

Hi Bjorn,

On Thu, Sep 12, 2024 at 3:05 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> 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 have the same feeling too. The PCIe spec doesn't specify what's the
correct power state for shutdown.
So we can only "logically" think the software should put devices to
low power state during shutdown.

>
> 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?

That was my first thought, so I modified pcie_port_shutdown_service()
to disable AER interrupt.
That approach didn't work though.

>
> My understanding is that .shutdown() should turn off device interrupts
> and stop DMA.  So maybe we need an aer_shutdown() that disables
> interrupts?

Logically we should do that. However that approach doesn't solve this issue.

>
> > 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
> >