Re: [PATCH] USB: serial: console: fix reported terminal settings

[Jarkko Nikula]

On 12/4/18 6:31 PM, Johan Hovold wrote:
> On Tue, Dec 04, 2018 at 05:15:18PM +0100, Greg Kroah-Hartman wrote:
> > On Tue, Dec 04, 2018 at 05:00:36PM +0100, Johan Hovold wrote:
> > > The USB-serial console implementation has never reported the actual
> > > terminal settings used. Despite storing the corresponding cflags in its
> > > struct console, this was never honoured on later tty open() where the
> > > tty termios would be left initialised to the driver defaults.
> > >
> > > Unlike the serial console implementation, the USB-serial code calls
> > > subdriver open() already at console setup. While calling set_termios()
> > > before open() looks like it could work for some USB-serial drivers,
> > > others definitely do not expect this, so modelling this after serial
> > > core is going to be intrusive, if at all possible.
> > >
> > > Instead, use a (renamed) tty helper to save the termios data used at
> > > console setup, so that the tty termios reflects the actual terminal
> > > settings after a subsequent tty open().
> > >
> > > Note that the calls to tty_init_termios() (tty_driver_install()) and
> > > tty_save_termios() are serialised using the disconnect mutex.
> > >
> > > This specifically fixes a regression that was triggered by a recent
> > > change adding software flow control to the pl2303 driver: a getty trying
> > > to disable flow control while leaving the baud rate unchanged would now
> > > also set the baud rate to the driver default (prior to the flow-control
> > > change this had been a noop).
> > >
> > > Fixes: 7041d9c3f01b ("USB: serial: pl2303: add support for tx xon/xoff flow control")
> > > Cc: stable <stable@xxxxxxxxxxxxxxx>	# 4.18
> > > Reported-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
> > > Cc: Florian Zumbiehl <florz@xxxxxxxx>
> > > Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
> > > ---
> > >   drivers/tty/tty_io.c         | 11 +++++++++--
> > >   drivers/usb/serial/console.c |  2 +-
> > >   include/linux/tty.h          |  1 +
> > >   3 files changed, 11 insertions(+), 3 deletions(-)
> >
> > Ah, messy :)
> >
> > Want me to take this through my tty tree?
>
> If you prefer. I was planning on including this in a USB-serial pull
> request for -rc6 since it fixes a user-reported regression, but perhaps
> taking this through your tty-linus branch (which already holds a console
> fix) is easier/faster.
>
> We should wait for Jarkko to confirm that this fixes the problem he
> reported first, though.
Great, this fixed the issue for both pl2303 based adapters I reported.

Tested on top of 0072a0c14d5b ("Merge tag 'media/v4.20-4' of 
git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media")

Tested-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>