Re: [PATCH 0/3] a family of FTDI-based devices that need ftdi_sio quirks

[Johan Hovold <johan@kernel.org>]

On Mon, Nov 30, 2020 at 12:15:51PM -0800, Mychaela Falconia wrote:

> > I'm adding a new tty port flag that can be used to suppress the
> > assertion of DTR/RTS to signal DTE readiness on open named NORDY.
> > Eventually we can expose it through termios to match HUPCL that controls
> > the behaviour on final close. For now I'm only adding a sysfs interface
> > but that also allows control over these signals on first open.
> 
> I don't see how exposing this new flag via termios would be of any use
> (it's a chicken and egg problem: one needs to open the tty device in
> order to do termios ioctls on it, and if that initial open triggers
> DTR/RTS hardware actions, then the end user is still screwed), but
> making this flag accessible for setting and clearing via sysfs is a
> good idea.

Yeah, as I mentioned in the other thread a termios flag would not be
sufficient for your use case, but there could be other applications that
are more tolerant but still want control after first open.

I believe this is also the way Win32, which you referred to earlier,
works.

Johan