On Sat, May 28, 2022 at 8:51 PM Mychaela N. Falconia
<falcon@xxxxxxxxxxxxxxx> wrote:
>
> There exist special serial devices (either attaching to generic serial
> ports or containing a built-in USB-serial chip) in which DTR and/or RTS
> have been repurposed for non-standard uses. Depending on exactly how
> these signals are repurposed, standard POSIX/SUS behaviour of
Which version of POSIX and SUS standards are in consideration?
> unconditionally raising both signals on open may range from harmless
> to undesirable to a total killer, precluding the use of Linux with
> such custom hardware.
>
> The newly added TTY_PORT_MANUAL_RTSDTR flag switches an individual
> serial port from POSIX/SUS standard to non-standard behaviour: when
> set, it suppresses the built-in action of raising DTR & RTS on serial
> port open.
>
> This flag can be exported through sysfs, and it can also be set by
> USB-serial device drivers when they see a custom hw device (identified
> by VID:PID) that is known to be wired in a way that requires this flag
> to be set.
Is it only the USB class of devices that are affected or do we have
examples on other buses?
...
> void tty_port_raise_dtr_rts(struct tty_port *port)
> {
> - if (port->ops->dtr_rts)
> + if (port->ops->dtr_rts && !tty_port_manual_rtsdtr(port))
> port->ops->dtr_rts(port, 1);
Logically I would put them otherwise, first to check a custom flag and
then the existence of the callback.
> }
--
With Best Regards,
Andy Shevchenko
