On Fri, 9 Feb 2024 10:35:21 -0600
Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> On Tue, Jan 23, 2024 at 11:55:31AM -0700, Alex Williamson wrote:
> > The commit noted in fixes added a bogus requirement that runtime PM
> > managed devices need to be in the RPM_ACTIVE state for PME polling.
> > In fact, only devices in low power states should be polled.
> >
> > However there's still a requirement that the device config space must
> > be accessible, which has implications for both the current state of
> > the polled device and the parent bridge, when present. It's not
> > sufficient to assume the bridge remains in D0 and cases have been
> > observed where the bridge passes the D0 test, but the PM state
> > indicates RPM_SUSPENDING and config space of the polled device becomes
> > inaccessible during pci_pme_wakeup().
> >
> > Therefore, since the bridge is already effectively required to be in
> > the RPM_ACTIVE state, formalize this in the code and elevate the PM
> > usage count to maintain the state while polling the subordinate
> > device.
>
> This apparently fixes a problem: the bugzilla says something about
> disks attached to Thunderbolt/USB4 docks not working, but I doubt it's
> actually specific to Thunderbolt/USB4 or to disks.
Right, AIUI it's simply a PCIe hierarchy where a bridge was previously
scanned in response to a PME and no longer is because of the invalid
requirement added in d3fcd7360338 that the runtime power management
status of the device is active.
> The bugzilla also indicates that d3fcd7360338 was a regression.
> d3fcd7360338 appeared in v6.6, so this fix is likely a candidate for
> the current release (v6.8).
Agreed.
> I'd like to mention both the user-visible problem being fixed and
> the fact that it fixes a regression here in the commit log so we can
> make the case for putting this in v6.8.
Ok, I've not experienced the regression myself, but I can add a
paragraph describing my understanding of the bugzilla. I'd probably
just say:
This resolves a regression reported in the bugzilla below where
a Thunderbolt/USB4 hierarchy fails to scan for an attached NVMe
endpoint downstream of a bridge in a D3hot power state.
If you'd like a respin including that or if you have further
phrasing/info suggestions, please let me know. Thanks,
Alex
> > Cc: Lukas Wunner <lukas@xxxxxxxxx>
> > Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> > Fixes: d3fcd7360338 ("PCI: Fix runtime PM race with PME polling")
> > Reported-by: Sanath S <sanath.s@xxxxxxx>
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218360
> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > ---
> > drivers/pci/pci.c | 37 ++++++++++++++++++++++---------------
> > 1 file changed, 22 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index bdbf8a94b4d0..764d7c977ef4 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -2433,29 +2433,36 @@ static void pci_pme_list_scan(struct work_struct *work)
> > if (pdev->pme_poll) {
> > struct pci_dev *bridge = pdev->bus->self;
> > struct device *dev = &pdev->dev;
> > - int pm_status;
> > + struct device *bdev = bridge ? &bridge->dev : NULL;
> > + int bref = 0;
> >
> > /*
> > - * If bridge is in low power state, the
> > - * configuration space of subordinate devices
> > - * may be not accessible
> > + * If we have a bridge, it should be in an active/D0
> > + * state or the configuration space of subordinate
> > + * devices may not be accessible or stable over the
> > + * course of the call.
> > */
> > - if (bridge && bridge->current_state != PCI_D0)
> > - continue;
> > + if (bdev) {
> > + bref = pm_runtime_get_if_active(bdev, true);
> > + if (!bref)
> > + continue;
> > +
> > + if (bridge->current_state != PCI_D0)
> > + goto put_bridge;
> > + }
> >
> > /*
> > - * If the device is in a low power state it
> > - * should not be polled either.
> > + * The device itself should be suspended but config
> > + * space must be accessible, therefore it cannot be in
> > + * D3cold.
> > */
> > - pm_status = pm_runtime_get_if_active(dev, true);
> > - if (!pm_status)
> > - continue;
> > -
> > - if (pdev->current_state != PCI_D3cold)
> > + if (pm_runtime_suspended(dev) &&
> > + pdev->current_state != PCI_D3cold)
> > pci_pme_wakeup(pdev, NULL);
> >
> > - if (pm_status > 0)
> > - pm_runtime_put(dev);
> > +put_bridge:
> > + if (bref > 0)
> > + pm_runtime_put(bdev);
> > } else {
> > list_del(&pme_dev->list);
> > kfree(pme_dev);
> > --
> > 2.43.0
> >
>
