Re: [PATCH v3 2/3] PCI/PM: Run bridge power up actions as part of restore phase

[Rafael J. Wysocki (Intel)]

On Mon, Aug 31, 2026 at 10:56 PM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
>
> From: "Mario Limonciello (AMD)" <superm1@xxxxxxxxxx>
>
> pci_pm_resume_noirq() calls pci_pm_bridge_power_up_actions() when a
> bridge is coming back from D3cold and bus PM was not skipped, so that
> the mandatory post-power-on link training delays are observed before
> any downstream device is accessed.
>
> The last patch in this series makes the hibernate poweroff_noirq path
> put bridges with downstream devices into D3 (including D3cold),
> mirroring what the S3 suspend path already does.  For that to be safe,
> the hibernate image restore path has to bring those bridges back up the
> same way suspend resume does; otherwise a downstream device may be
> accessed before its parent bridge's link is retrained.

Note though that pci_pm_restore_noirq() runs after the boot kernel has
initialized the PCI bus, so all of the links should be retrained by
that time.

It then carries out a "freeze" transition before passing control to
the image kernel, so "restore" doesn't really get devices in
"pristine" states.

Moreover, BIOS code runs before "poweroff_noirq" and the boot kernel
and it also messes up with devices in general.

Is there a specific issue that is avoided by this change?

> Add the same bridge power up actions to pci_pm_restore_noirq(), gated on
> the same conditions as the resume path (bus PM not skipped and the
> previous state being D3cold), so that hibernate restore and suspend
> resume behave identically for bridges.
>
> Tested-by: Eric Naim <dnaim@xxxxxxxxxxx>
> Signed-off-by: Mario Limonciello (AMD) <superm1@xxxxxxxxxx>
> ---
>  drivers/pci/pci-driver.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index e3d352c7b31d4..d15b3eb55ec53 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1297,10 +1297,15 @@ static int pci_pm_restore_noirq(struct device *dev)
>  {
>         struct pci_dev *pci_dev = to_pci_dev(dev);
>         const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> +       pci_power_t prev_state = pci_dev->current_state;
> +       bool skip_bus_pm = pci_dev->skip_bus_pm;
>
>         pci_pm_default_resume_early(pci_dev);
>         pci_fixup_device(pci_fixup_resume_early, pci_dev);
>
> +       if (!skip_bus_pm && prev_state == PCI_D3cold)
> +               pci_pm_bridge_power_up_actions(pci_dev);
> +
>         if (pci_has_legacy_pm_support(pci_dev))
>                 return 0;
>
> --
> 2.43.0
>