Hello,
We run Linux as a VM on top of the Muen Separation Kernel [1] where we
have implemented PCI device passthrough using VT-d.
I have come across an issue where USB ports of an assigned xHCI
controller are no longer being enabled in recent kernels (tested with
v3.18.3 and v3.19-rc5) while it is working in v3.11. I did a bisect and
identified commit 26b7679 ("Intel xhci: refactor EHCI/xHCI port
switching") as the cause. Upon closer inspection the relevant part of
the change seems to be in drivers/usb/host/pci-quirks.c:
void usb_enable_intel_xhci_ports(struct pci_dev *xhci_pdev)
{
...
/* make sure an intel EHCI controller exists */
for_each_pci_dev(companion) {
if (companion->class == PCI_CLASS_SERIAL_USB_EHCI &&
companion->vendor == PCI_VENDOR_ID_INTEL) {
ehci_found = true;
break;
}
}
if (!ehci_found)
return;
...
}
In our test case we only grant Linux access to the xHCI but *not* the
EHCI controller. Since ehci_found is never true in this case the xHCI
ports will not be enabled. Commenting out the return statement results
in working xHCI ports.
Is there a different way to decide whether xHCI ports should be enabled
instead of looking for a companion EHCI controller or must the xHCI and
EHCI controllers always be accessible at the same time?
I suspect that the issue is also relevant for other hypervisors that
allow PCI passthrough in a similar fashion.
Note: I am not subscribed to the linux-usb mailing list, please keep me
as CC.
Regards,
Adrian
[1] - http://muen.codelabs.ch/
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