tty: n_gsm line discipline

Add an implementation of GSM 0710 MUX. The implementation currently supports

- Basic and advanced framing (as either end of the link)
- UI or UIH data frames
- Adaption layer 1-4 (1 and 2 via tty, 3 and 4 as skbuff lists)
- Modem and control messages including the correct retry process
- Flow control

and exposes the MUX channels as a set of virtual tty devices including modem
signals. This is an experimental driver.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 7e605e4b3da3..931078b73226 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -48,6 +48,7 @@
 #define N_PPS           18      /* Pulse per Second */
 #define N_V253          19      /* Codec control over voice modem */
 #define N_CAIF          20      /* CAIF protocol for talking to modems */
+#define N_GSM0710       21      /* GSM 0710 Mux */
 
 /*
  * This character is the same as _POSIX_VDISABLE: it cannot be used as