Console output stops on dbgp=xhci

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

Hi Marek,
I'm testing the latest Xen master git branch
(942ac5fc15ecc2f7ef1d9331c76d89d2cef10e5c) with the now merged xue
patches.  My current boot command line includes dbgp=xhci@pci00:14.0
console=dbgp and this works in that the Xen boot log shows up on the
other side of the debug cable:

...

(XEN) Dom0 has maximum 8 VCPUs

(XEN) ELF: phdr 0 at 0xffffffff81000000 -> 0xffffffff82c5cdac

(XEN) ELF: phdr 1 at 0xffffffff82e00000 -> 0xffffffff831a1000

(XEN) ELF: phdr 2 at 0xffffffff831a1000 -> 0xffffffff831d5000

(XEN) ELF: phdr 3 at 0xffffffff831d5000 -> 0xffffffff84000000

However, debug output on the USB3 port stops at this point. I would
expect to see the same as xl dmesg shows:

(XEN) Dom0 has maximum 8 VCPUs
(XEN) ELF: phdr 0 at 0xffffffff81000000 -> 0xffffffff82c5cdac
(XEN) ELF: phdr 1 at 0xffffffff82e00000 -> 0xffffffff831a1000
(XEN) ELF: phdr 2 at 0xffffffff831a1000 -> 0xffffffff831d5000
(XEN) ELF: phdr 3 at 0xffffffff831d5000 -> 0xffffffff84000000
(XEN) Initial low memory virq threshold set at 0x4000 pages.
(XEN) Scrubbing Free RAM in background
(XEN) Std. Loglevel: All
(XEN) Guest Loglevel: All
(XEN) *** Serial input to DOM0 (type 'CTRL-a' three times to switch input)
(XEN) Freed 2048kB init memory
...

Do you have any idea what might be going on and preventing the output
from showing over USB3 afterwards? The /dev/ttyUSB0 device is still
present on the receiving side, just nothing is being received over it.

Thanks,
Tamas