Serial console via USB (USBTTY) ...

Herbert Poetzl herbert at
Thu Apr 1 20:45:16 CEST 2021

On Thu, Apr 01, 2021 at 07:36:14PM +0300, Andy Shevchenko wrote:
> On Thu, Apr 1, 2021 at 7:17 PM Herbert Poetzl <herbert at> wrote:

>> Hello Andy!

>> Thanks for the quick feedback!

>> On Thu, Apr 01, 2021 at 04:10:57PM +0300, Andy Shevchenko wrote:
>>> On Thu, Apr 1, 2021 at 2:19 PM Herbert Poetzl <herbert at> wrote:

>>>> 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_USBD_HS (for high speed support)

>>>> ... but when doing so, I get a number of linker errors
>>>> which suggest that there is something missing:

>>>> 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.

>>> Precisely!

>> Are there any examples of such a conversion or is there
>> some guide how to convert drivers from the 'old' framework
>> 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 ...

>>> I abandoned that, but I can send what I have (it still doesn't
>>> properly work to me).

>> Would definitely be interesting to see, as it seems that
>> other function drivers (those are the f_* ones, as far
>> as I understood) seem to work just fine.

> Here you are:

> No guarantees or anything. It's a pile of something.
> Tell me when you get it, so I will remove the branch (let's say
> I'll do it within 24 hours anyway).

Got it, thanks!

>>>> So my questions are:

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

>>> Create a support for it.
>>> You may consider it as there is no support.

>> Okay, how do I best start with that?

> Try to read the code of existing functions in U-Boot and Linux
> kernel?

Yeah, is there a specific function driver which was ported
from Linux to U-Boot already or would the serial driver 
be the first one?

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

>>> Not from me (I started but encountered so many issues here and
>>> there, besides the fact that it's really time consuming).

>> I understand ...

>>>>  - Can I help getting this working?

>>> If you do it yourself. I can help with testing on my platform.

>> Great! Thanks in advance!

Thanks a bunch,

>> Best,
>> Herbert

>>> --
>>> With Best Regards,
>>> Andy Shevchenko

> -- 
> With Best Regards,
> Andy Shevchenko

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