On Fri, 2020-07-10 at 11:54 +0200, Johan Hovold wrote:
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>
> On Fri, Jul 10, 2020 at 11:35:18AM +0200, Joakim Tjernlund wrote:
> > BO will disable USB input until the device opens. This will
> > avoid garbage chars waiting flood the TTY. This mimics a real UART
> > device better.
> > For initial termios to reach USB core, USB driver has to be
> > registered before TTY driver.
> >
> > Signed-off-by: Joakim Tjernlund <joakim.tjernlund@xxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> >
> > I hope this change makes sense to you, if so I belive
> > ttyUSB could do the same.
>
> No, this doesn't make sense. B0 is used to hang up an already open tty.
This is at module init so there is no tty yet.
acm_probe() will later set:
acm->line.dwDTERate = cpu_to_le32(9600);
acm->line.bDataBits = 8;
acm_set_line(acm, &acm->line);
>
> Furthermore, this change only affects the initial terminal settings and
> won't have any effect the next time you open the same port.
hmm, it is not ideal but acm_probe() will later set:
acm->line.dwDTERate = cpu_to_le32(9600);
acm->line.bDataBits = 8;
acm_set_line(acm, &acm->line);
But, would it not make sense to not accept input until TTY is opened ?
That would be more inline with a real RS232, would it not?
>
> Why not fix your firmware so that it doesn't transmit before DTR is
> asserted during open()?
I would but it is not my firmware, it is a ready made USB to UART chip. will talk
to the manufacturer though.
> > drivers/usb/class/cdc-acm.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> > index 751f00285ee6..5680f71200e5 100644
> > --- a/drivers/usb/class/cdc-acm.c
> > +++ b/drivers/usb/class/cdc-acm.c
> > @@ -1999,19 +1999,19 @@ static int __init acm_init(void)
> > acm_tty_driver->subtype = SERIAL_TYPE_NORMAL,
> > acm_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
> > acm_tty_driver->init_termios = tty_std_termios;
> > - acm_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD |
> > + acm_tty_driver->init_termios.c_cflag = B0 | CS8 | CREAD |
> > HUPCL | CLOCAL;
> > tty_set_operations(acm_tty_driver, &acm_ops);
> >
> > - retval = tty_register_driver(acm_tty_driver);
> > + retval = usb_register(&acm_driver);
> > if (retval) {
> > put_tty_driver(acm_tty_driver);
> > return retval;
> > }
> >
> > - retval = usb_register(&acm_driver);
> > + retval = tty_register_driver(acm_tty_driver);
> > if (retval) {
> > - tty_unregister_driver(acm_tty_driver);
> > + usb_deregister(&acm_driver);
> > put_tty_driver(acm_tty_driver);
> > return retval;
> > }
>
> Johan
