Re: [PATCH] PCI/portdrv: Disallow runtime suspend when waekup is required but PME service isn't supported

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

On Mon, Aug 9, 2021 at 5:47 PM Lukas Wunner <lukas@wunner.de> wrote:
>
> [cc += Mika]
>
> On Mon, Aug 09, 2021 at 12:24:12PM +0800, Kai-Heng Feng wrote:
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=213873
>
> The last comment on this bugzilla says "BIOS will fix this."
> and the status is RESOLVED WILL_NOT_FIX.
>
> Why is the patch still necessary?

Well, let me update the bug report.

>
>
> > Some platforms cannot detect ethernet hotplug once its upstream port is
> > runtime suspended because PME isn't enabled in _OSC.
>
> If PME is not handled natively, why does the NIC runtime suspend?
> Shouldn't this be fixed in the NIC driver by keeping the device
> runtime active if PME cannot be used?

That means we need to fix every user of pci_dev_run_wake(), or fix the
issue in pci_dev_run_wake() helper itself.
However, I am afraid that implementing the fix in pci_dev_run_wake()
may break the while loop check:
bool pci_dev_run_wake(struct pci_dev *dev)
{
 ...
        while (bus->parent) {
                struct pci_dev *bridge = bus->self;

                if (device_can_wakeup(&bridge->dev))
                        return true;

                bus = bus->parent;
...
}

So I took the current approach.

>
>
> > Disallow port runtime suspend when any child device requires wakeup, so
> > pci_pme_list_scan() can still read the PME status from the devices
> > behind the port.
>
> pci_pme_list_scan() is for broken devices which fail to signal PME.
> Is this NIC really among them or does PME fail merely because it's not
> granted to OSPM?

The latter, PME IRQ isn't enabled because it's not granted by BIOS _OSC.

>
>
> > --- a/drivers/pci/pcie/portdrv_pci.c
> > +++ b/drivers/pci/pcie/portdrv_pci.c
> > @@ -59,14 +59,30 @@ static int pcie_port_runtime_suspend(struct device *dev)
> >       return pcie_port_device_runtime_suspend(dev);
> >  }
> >
> > +static int pcie_port_wakeup_check(struct device *dev, void *data)
> > +{
> > +     struct pci_dev *pdev = to_pci_dev(dev);
> > +
> > +     if (!pdev)
> > +             return 0;
> > +
> > +     return pdev->wakeup_prepared;
> > +}
> > +
> >  static int pcie_port_runtime_idle(struct device *dev)
> >  {
> > +     struct pci_dev *pdev = to_pci_dev(dev);
> > +
> > +     if (!pcie_port_find_device(pdev, PCIE_PORT_SERVICE_PME) &&
> > +         device_for_each_child(dev, NULL, pcie_port_wakeup_check))
> > +             return -EBUSY;
> > +
> >       /*
> >        * Assume the PCI core has set bridge_d3 whenever it thinks the port
> >        * should be good to go to D3.  Everything else, including moving
> >        * the port to D3, is handled by the PCI core.
> >        */
> > -     return to_pci_dev(dev)->bridge_d3 ? 0 : -EBUSY;
> > +     return pdev->bridge_d3 ? 0 : -EBUSY;
>
> If an additional check is necessary for this issue, it should be
> integrated into pci_dev_check_d3cold() instead of pcie_port_runtime_idle().

I think PME IRQ and D3cold are different things here.
The root port of the affected NIC doesn't support D3cold because
there's no power resource.

Kai-Heng

>
> Thanks,
>
> Lukas