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tty: n_gsm: add RING/CD control support 

The status lines ring and carrier detect are used by the modem to signal
incoming calls (RING) or an established connection (CD). This is
implemented as physical lines on a standard RS232 connection. However,
the muxer protocol encodes these status lines as modem bits IC and DV.
These incoming lines are masked by tty driver (see tty_io.c) and cannot be
set by a user application.

Allow setting RING via TIOCM_OUT1 and CD via TIOCM_OUT2 to allow
implementation of a modem or modem emulator.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20230206114606.2133-3-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Starke 2023-02-06 12:46:05 +01:00 committed by Greg Kroah-Hartman
parent 9bd6dcb8cc
commit 42ec0b93e4
1 changed files with 5 additions and 0 deletions
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5
drivers/tty/n_gsm.c
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@ -540,6 +540,11 @@ static u8 gsm_encode_modem(const struct gsm_dlci *dlci)
modembits |= MDM_IC;
if (dlci->modem_tx & TIOCM_CD || dlci->gsm->initiator)
modembits |= MDM_DV;
/* special mappings for passive side to operate as UE */
if (dlci->modem_tx & TIOCM_OUT1)
modembits |= MDM_IC;
if (dlci->modem_tx & TIOCM_OUT2)
modembits |= MDM_DV;
return modembits;
}