Re: [PATCH v3] PCI/PM: Restore BARs after powering up during enumeration

[Desnes Nunes]

Reviewed-by: Desnes Nunes <desnesn@xxxxxxxxxx>


Desnes Nunes


On Thu, Oct 15, 2026 at 11:15 AM Rafael J. Wysocki (Intel)
<rafael@xxxxxxxxxx> wrote:
>
> On Thu, Oct 15, 2026 at 4:08 AM Keng-Yu Lin <keng-yu.lin@xxxxxxx> wrote:
> >
> > Commit 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when
> > initializing") added pci_pm_power_up_and_verify_state() to pci_pm_init().
> > The helper ignores pci_power_up()'s return value indicating that BARs
> > need restoring. Its resume callers restore saved configuration
> > afterwards; pci_pm_init() does not.
> >
> > D3hot-to-D0 may reset a device and lose its BARs (PCI PM 1.2, sec 5.4.1).
> > After enumeration powers it up, pci_enable_device() reads D0 and skips
> > the full power-up path. Previously, a device still in D3hot at enable
> > time took that path, including BAR restoration.
> >
> > On AMD Venice SP7, two AMD xHCI controllers [1022:17d2] are in runtime
> > D3hot with No_Soft_Reset clear before kdump. Diagnostic reads on
> > v7.3-rc6-37 show the following for 0000:01:00.4 in the crash kernel:
> >
> >                                    PMCSR      BAR0
> >   before the platform power call   0003       f4100004
> >   after the platform power call    0003       f4100004
> >   after native D0 power-up         0000       00000004
> >
> > The upper BAR DWORD stays zero. pci_power_up() returns 1, but the BAR
> > address remains zero while dev->resource[0] still contains 0xf4100000.
> > Without BAR restoration, the crash kernel hangs during boot. The
> > last console output includes:
> >
> >   pci 0000:01:00.4: enabling device (0000 -> 0002)
> >
> > Restoring both controllers' BARs gives matching readbacks and allows
> > kdump to save a vmcore and reboot. An AMD Turin xHCI [1022:1557] shows
> > the same BAR loss; restoring its BAR also allows kdump to complete.
> >
> > Read the initial power state first. Otherwise, pci_power_up() may
> > request a BAR restore based on a cached PCI_UNKNOWN state, even
> > when the device is already in D0.
> >
> > For devices already in D0, only synchronize the platform state so
> > that ACPI calls such as _REG still run. For other states, use
> > pci_set_full_power_state() to power up the device and restore BARs
> > when needed.
> >
> > Suggested-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > Suggested-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> > Fixes: 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when initializing")
> > Link: https://lore.kernel.org/r/CAJZ5v0ie2AvCbdv8-zkpYzHLcTwUPUj+=WWOQjDAPmSepSAQPg@xxxxxxxxxxxxxx/
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Keng-Yu Lin <keng-yu.lin@xxxxxxx>
>
> Reviewed-by: Rafael J. Wysocki (Intel) <rafael@xxxxxxxxxx>
>
> > ---
> >
> > Changes in v3:
> > - Use Rafael's sequence: sync only the platform state for devices
> >   already in D0, and use pci_set_full_power_state() otherwise.
> > - The D0 path no longer runs the full helper's ASPM update.
> >
> > Tested with diagnostic prints on AMD Venice SP7 and Turin. Normal
> > boots made no BAR writes from this path. The crash kernels restored
> > only the cleared xHCI BARs (two on Venice, one on Turin), with matching
> > readbacks. Both systems saved a vmcore and rebooted.
> >
> > v2: https://lore.kernel.org/r/20261012104645.975190-1-keng-yu.lin@xxxxxxx/
> >
> >  drivers/pci/pci.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 8cc6a89130b5..895969fe4520 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -3255,7 +3255,15 @@ void pci_pm_init(struct pci_dev *dev)
> >         }
> >
> >  poweron:
> > -       pci_pm_power_up_and_verify_state(dev);
> > +       pci_update_current_state(dev, PCI_UNKNOWN);
> > +       if (dev->current_state == PCI_D0) {
> > +               /* No need to do a full power-up, just sync-up the platform state. */
> > +               platform_pci_set_power_state(dev, PCI_D0);
> > +       } else {
> > +               /* Power up the device and restore BARs if necessary. */
> > +               pci_set_full_power_state(dev, false);
> > +       }
> > +       pci_update_current_state(dev, PCI_D0);
> >         pm_runtime_forbid(&dev->dev);
> >
> >         /*
> >
> > base-commit: 7b63ef2d55f24519e7e9e5f4d15dbea03f126e40
> > --
> > 2.43.0
>