tty: n_gsm: fix missing modem controls after DLCI open in convergence layer type 2

The current implementation only updates the virtual V.24 control signals
after DLCI open in basic option mode. In advanced option mode with
convergence layer type 2 an empty data frame needs to be transmitted to
inform the peer about the initial virtual V.24 control signals. Not doing
so has two unwanted side effects:
1. hardware flow control status is unclear (initial CTS line is unknown)
2. DLCI user presence is not transmitted (initial DTR line is unknown)

Applications waiting on these lines can not start after a DLCI has been
opened until the first data frame has been transmitted.

Fix this by using gsm_modem_update() thoroughly which handles basic and
advanced option mode correctly. Add a flag in gsm_modem_update() and the
delegated gsm_modem_upd_via_msc() to control whether waiting for the MSC
command response is possible. Remove obsolete gsm_modem_send_initial_msc().

Fixes: 3cf0b3c243e5 ("tty: n_gsm: Don't block input queue by waiting MSC")
Cc: stable <stable@kernel.org>
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://patch.msgid.link/20260826063026.2472-1-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions