Hi Mario, On Wed, Nov 15, 2023 at 11:08:43AM -0600, Mario Limonciello wrote: > On 11/15/2023 04:40, Mika Westerberg wrote: > > Hi Mario, > > > > On Tue, Nov 14, 2023 at 02:07:53PM -0600, Mario Limonciello wrote: > > > USB4 routers support a feature called "PCIe tunneling". This > > > allows PCIe traffic to be transmitted over USB4 fabric. > > > > > > PCIe root ports that are used in this fashion can be discovered > > > by device specific data that specifies the USB4 router they are > > > connected to. For the PCI core, the specific connection information > > > doesn't matter, but it's interesting to know that this root port is > > > used for tunneling traffic. This will allow other decisions to be > > > made based upon it. > > > > > > Detect the `usb4-host-interface` _DSD and if it's found save it > > > into a new `is_virtual_link` bit in `struct pci_device`. > > > > While this is fine for the "first" tunneled link, this does not take > > into account possible other "virtual" links that lead to the endpoint in > > question. Typically for eGPU it only makes sense to plug it directly to > > the host but say there is a USB4 hub (with PCIe tunneling capabilities) > > in the middle. Now the link from the hub to the eGPU that is also > > "virtual" is not marked as such and the bandwidth calculations may not > > get what is expected. > > Right; you mentioned the DVSEC available for hubs in this case. As I don't > have one of these to validate it works properly I was thinking that should > be a follow up. > > If you think it should be part of the same series I'll add it, but I'd ask > if you can please check I did it right on one that reports the DVSEC? I don't think it should be part of this series. I just checked and DVSEC is only required for hosts so kind of hardware equivalent for the _DSD property you are using here. For hubs there is no such luxury unfortunately. I think I do have hardware here with the DVSEC in place so if you decide to add it, I should be able to try it.
