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

[Seth Forshee]

On Fri, Mar 08, 2019 at 11:46:42PM +0100, Rene 'Renne' Bartsch, B.Sc. Informatics wrote:
> 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.

USB_XHCI_DBGCAP has been enabled since cosmic. I've now enabled
CONFIG_EARLY_PRINTK_USB_XDBC as well in disco.

To enable this in the cosmic 4.18 kernels we need a bug report. You can
file a bug here:

 https://bugs.launchpad.net/ubuntu/+source/linux/+filebug

Thanks,
Seth