Re: ttyACM: disabled by hub (EMI?), re-enabling... Causes garbage chars & disconnect

[Joakim Tjernlund <Joakim.Tjernlund@infinera.com>]

On Wed, 2020-05-27 at 12:41 +0200, Oliver Neukum wrote:
> Am Mittwoch, den 27.05.2020, 09:40 +0000 schrieb Joakim Tjernlund:
> > On Wed, 2020-05-27 at 10:38 +0200, Oliver Neukum wrote:
> > > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> > > 
> > > 
> > > Am Dienstag, den 26.05.2020, 17:19 +0000 schrieb Joakim Tjernlund:
> > > > This "u-boot SPL" is the first thing u-boot writes and somehow this is remembered, I assume, by cdc_acm
> > > > and gets echoed back when I open ttyACM0
> > > 
> > > Hi,
> > > 
> > > that makes sense, but it is not something that we could really
> > > change in CDC-ACM, I am afraid.
> > 
> > Why not? CDC-ACM should echo back anything it has received before open of ttyACM
> 
> Well, there is an inherent race condition with loading the module I am
> afraid. By default cdc-acm should actually echo. You can set the
> DISABLE_ECHO echo quirk for your device if you want to get rid of it.
> 
> Is CDC-ACM violating some standard with respect to echoing? Changing
> defaults really hurts users, no matter what you do.
> 


	/*
	 * Suppress initial echoing for some devices which might send data
	 * immediately after acm driver has been installed.
	 */
	if (acm->quirks & DISABLE_ECHO)
		tty->termios.c_lflag &= ~ECHO;

That seems to be what I needed, should be default I think ...
Need to test som more but looks much better.
I guess all cdc_acm's are could suffer from this? Will depend the target in the other
end.

 Jocke