USB: serial: console: fix reported terminal settings

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

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@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>