Re: [PATCH v5] USB: serial: add Moxa UPORT 11x0 driver

[Johan Hovold <johan@kernel.org>]

On Mon, Dec 28, 2015 at 02:39:44PM +0000, One Thousand Gnomes wrote:
> > 	https://lkml.kernel.org/r/201102171210.03474.frode@tennebo.com
> > 
> > However, the TIOCSRS485-ioctl might not even be the right interface for
> > changing transceiver modes, and instead a sysfs-based
> > usb-serial-specific interface could be more appropriate for example.
> 
> sysfs works out very badly if modes can be configured routinely at
> runtime. In particular the sysfs interface is completely disconnected
> from the vhangup() and security model of the tty interface.
> 
> If its the kind if thing just administratively configured at boot then
> it's a great interface, just be careful about who has access to it.

I think this is something that you only want to configure once (e.g. at
boot) and before even opening the tty device as this can change the
functions of the pins (e.g. DCD becoming TxD-).

If a generic usb-serial-specific interface for this makes sense, I think
we should simply prevent mode changes while the port is in use.

Johan