On Thu, Jan 31, 2019 at 04:18:33PM +0100, Marcel Holtmann wrote:

quoted

I agree with Al that this change doesn't make much sense. The WARN_ON
is there to catch any bugs leading to the termios being changed for a
master side pty. Those should bugs should be fixed, and not worked
around in order to silence a WARN_ON.

The problem started with 7721383f4199 ("Bluetooth: hci_uart: Support
operational speed during setup") which introduced a new way for how
tty_set_termios() could end up being called for a master pty.

As Al hinted at, setting these ldiscs for a master pty really makes no
sense and perhaps that is what we should prevent unless simply making
sure they do not call tty_set_termios() is sufficient for the time
being.

Finally, note that serdev never operates on a pty, and that this is only
an issue for (the three) line disciplines.

I think for PTYs we should just fail setting the HCI line discipline.
Fail early and just move on with life.

Sounds good to me. At least for the pty master. There may be some people
trying to use a bluetooth device connected to a remote serial port (I've
seen descriptions of such setups at least), and maybe we need not prevent
that.

Johan