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 <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/char/Kconfig

@@ -276,11 +276,18 @@ config N_HDLC
 	  Allows synchronous HDLC communications with tty device drivers that
 	  support synchronous HDLC such as the Microgate SyncLink adapter.
 
-	  This driver can only be built as a module ( = code which can be
+	  This driver can be built as a module ( = code which can be
 	  inserted in and removed from the running kernel whenever you want).
 	  The module will be called n_hdlc. If you want to do that, say M
 	  here.
 
+config N_GSM
+	tristate "GSM MUX line discipline support (EXPERIMENTAL)"
+	depends on EXPERIMENTAL
+	help
+	  This line discipline provides support for the GSM MUX protocol and
+	  presents the mux as a set of 61 individual tty devices.
+
 config RISCOM8
 	tristate "SDL RISCom/8 card support"
 	depends on SERIAL_NONSTANDARD

drivers/char/Makefile

@@ -40,6 +40,7 @@ obj-$(CONFIG_SYNCLINK)		+= synclink.o
 obj-$(CONFIG_SYNCLINKMP)	+= synclinkmp.o
 obj-$(CONFIG_SYNCLINK_GT)	+= synclink_gt.o
 obj-$(CONFIG_N_HDLC)		+= n_hdlc.o
+obj-$(CONFIG_N_GSM)		+= n_gsm.o
 obj-$(CONFIG_AMIGA_BUILTIN_SERIAL) += amiserial.o
 obj-$(CONFIG_SX)		+= sx.o generic_serial.o
 obj-$(CONFIG_RIO)		+= rio/ generic_serial.o