[PATCH 3/3] cmd: add acmconsole command

[Loic Poulain]

Hi Pali,

Sorry for the late reply,

On Mon, 27 Sept 2021 at 22:04, Pali Rohár <pali at kernel.org> wrote:
>
> On Thursday 19 August 2021 13:13:06 Loic Poulain wrote:
> > This command allows to start CDC ACM function and redirect console
> > (stdin, stdout, stderr) to USB (acmconsole start). The console can
> > then be accessed through the USB host for debugging purpose. The
> > host can stop the session (acmconsole stop) to revert back console
> > to serial and unregister CDC ACM USB function.
>
> Hello!
>
> Could you rather implement this CDC ACM gadget in a way that calling
> 'setenv stdout cdc_acm' (or 'setenv stdout usbtty') would do this
> console redirect? Like it is supported for current usbtty or vga output
> code.
>
> Then this acmconsole command would not be needed at all.

Yes, that would be good, but AFAIR I restricted this cdc_acm usage to
this command because we can't have fine grained control like e.g.
using cdc_acm as stdout only, when used, it should necessarily be
STDIN (at least). The reason is because of the single-tasking nature
of u-boot, and the fact that we need to poll the USB controller for
events via the 'usb_gadget_handle_interrupts()' function. In our case
we simply do that in the getc() function, which is only called for
input consoles in the u-boot mainloop.

An alternative would be to have a u-boot API to register generic
callbacks to be executed in the mainloop, but this is probably a
different thread.

Also we could possibly live with this 'bug' and simply accept that
stdout-only configuration will be broken.

Regards,
Loic