Re: [PATCH 02/21] PCI: Add API to track PCI devices preserved across Live Update

[Lukas Wunner <lukas@wunner.de>]

On Tue, Dec 02, 2025 at 08:36:53PM +0400, Chris Li wrote:
> On Tue, Dec 2, 2025 at 6:59 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
> > The device is active
> > during KHO, you CAN NOT do any resource reassignment, not bus numbers,
> > not mmio. It must be fully disabled.
> 
> I agree with Jason. The bus number is used in the low level hardware
> to do the DMA transfer. The bus number can not change for a device
> during livedupate with pending DMA transfer. The BDF MUST remain the
> same as the liveupdate with DMA transfer requirement.

Thank you both for the explanation.

> Another point is that, on the same machine it can have multiple PCI
> host bridges. Each PCI host bridge bus number is acquired from the
> ACPI table walk. I am not aware of any way to get the slot number of
> the PCI host bridge. Lukas, do you know how to get the PCI host bridge
> slot number to form a path?

Host bridges are identified by the segment number.  On ACPI-based systems,
it's retrieved by acpi_pci_root_add() through invocation of the _SEG method.

Thanks,

Lukas