Enable kernel options CONFIG_EARLY_PRINTK_USB_XDBC and USB_XHCI_DBGCAP for serial Superspeed(+) connections with kernels >= 4.16

[Rene 'Renne' Bartsch, B.Sc. Informatics]

Hi,

since kernel 4.13 Linux supports an USB debug console with passive USB 3.x host-to-host cables aka "USB 3.0 super-speed A-to-A debugging cable".
Beginning with kernel 4.16 a serial port (/dev/ttyDbC) has been added (https://www.kernel.org/doc/html/v4.16/driver-api/usb/usb3-debug-port.html#serial-tty).

I suggest to enable USB DbC by enabling the kernel options "CONFIG_EARLY_PRINTK_USB_XDBC=Y" and "USB_XHCI_DBGCAP=Y" in Ubuntu kernels >= 4.16.

It would also be great to get feedback about line speed as USB_XHCI_DBGCAP serial ports can e.g. be used for network connections via tun/tap devices.


Regards,

Renne

P.S.: Don't use simple A-to-A USB cables for USB 3.x slave devices as they can fry your hardware. See cable specs in section 5.5.2 of the USB 3.0 specification (https://i.stack.imgur.com/YwsX3.png).