Serial console via USB (USBTTY) ...

[Herbert Poetzl]

I'm trying to get a serial console via USB working on
STM32MP1 but I'm encountering some problems there ...

The u-boot README suggests to add the following config
entries to the board specific .h file:

 CONFIG_USB_DEVICE
 CONFIG_USB_TTY
 CONFIG_USBD_HS (for high speed support)
 CONFIG_SYS_CONSOLE_IS_IN_ENV

... but when doing so, I get a number of linker errors
which suggest that there is something missing:
https://pastebin.com/raw/bbpCu8jy

Marek (via IRC) suggested that this is because the
USB_TTY seems to be based on the old gadget framework
and needs to be updated to the new one.

It was also suggested that a port of the Linux serial
function driver would be a good alternative to get
CDC/ACM functionality into u-boot and that Andy might
already be working on this ...

So my questions are:

 - What is currently the best/easiest approach to
   get a serial console via USB working?

 - Is the port from Linux in a stage that it can
   be tested and/or finalized within a easonable
   amount of time?

 - Can I help getting this working?

Thanks in advance,
Herbert