Re: [PATCH v6] PCI/PM: Skip resuming to D0 if disconnected

Bjorn Helgaas
2025-09-08T21:04:00Z

On Mon, Aug 11, 2025 at 11:35:10AM -0500, Mario Limonciello (AMD) wrote:
> When a USB4 dock is unplugged the PCIe bridge it's connected to will
> issue a "Link Down" and "Card not detected event". The PCI core will
> treat this as a surprise hotplug event and unconfigure all downstream
> devices. This involves setting the device error state to
> `pci_channel_io_perm_failure` which pci_dev_is_disconnected() will check.

There's nothing special about USB4 here, right? I guess the same
happens with any surprise hotplug remove?

pciehp_unconfigure_device() does the pci_dev_set_io_state(dev,
pci_channel_io_perm_failure) part on everything that got removed, so
that part is pretty straightforward.

> It doesn't make sense to runtime resume disconnected devices to D0 and
> report the (expected) error, so bail early.

Can you include a hint about where the runtime resume happens? It
seems unintuitive to power up removed devices.

> Suggested-by: Lukas Wunner <lukas@wunner.de>
> Reviewed-by: Lukas Wunner <lukas@wunner.de>
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Acked-by: Rafael J. Wysocki <rafael@kernel.org>
> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
> v6:
> * rebase on v6.17-rc1
> v5:
> * Pick up tags, rebase on linux-next
> * https://lore.kernel.org/linux-pci/20250709205948.3888045-1-superm1@kernel.org/T/#mbd784f786c50a3d1b5ab1833520995c01eae2fd2
> ---
> drivers/pci/pci.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b0f4d98036cdd..036511f5b2625 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1374,6 +1374,11 @@ int pci_power_up(struct pci_dev *dev)
> return -EIO;
> }
>
> + if (pci_dev_is_disconnected(dev)) {
> + dev->current_state = PCI_D3cold;
> + return -EIO;
> + }
> +
> pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
> if (PCI_POSSIBLE_ERROR(pmcsr)) {
> pci_err(dev, "Unable to change power state from %s to D0, device inaccessible\n",
>
> base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
> --
> 2.43.0
>