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

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

On Wed, 2020-05-27 at 15:16 +0200, Joakim Tjernlund wrote:
> 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.
> 

Would be nice if the ECHO could be delay until first read(2)/termios_set, the baudrate could be 11500 until open(2) too, maybe

However, the bigger question: Is the a way to configure Windows to default to ~ECHO too ?

    Jocke