USB: serial: console: fix reported terminal settings

[Johan Hovold <johan@kernel.org>]

On Wed, Dec 05, 2018 at 11:36:52AM +0200, Jarkko Nikula wrote:
> 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.

> >>> 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@vger.kernel.org>	# 4.18
> >>> Reported-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> >>> Cc: Florian Zumbiehl <florz@florz.de>
> >>> Signed-off-by: Johan Hovold <johan@kernel.org>
> >>> ---
> >>>   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@linux.intel.com>

Great, thanks for testing.

Greg, I noticed I left out the part about subdrivers not expecting
*write()* to be called before open() so I'll amend the commit message
when applying and include this one in a pull-request tomorrow, if that's
ok with you?

Note that the changes to tty are trivial; I'm just renaming and
exporting an existing helper.

Thanks,
Johan