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>

include/linux/gsmmux.h

@@ -0,0 +1,25 @@
+#ifndef _LINUX_GSMMUX_H
+#define _LINUX_GSMMUX_H
+
+struct gsm_config
+{
+	unsigned int adaption;
+	unsigned int encapsulation;
+	unsigned int initiator;
+	unsigned int t1;
+	unsigned int t2;
+	unsigned int t3;
+	unsigned int n2;
+	unsigned int mru;
+	unsigned int mtu;
+	unsigned int k;
+	unsigned int i;
+	unsigned int unused[8];		/* Padding for expansion without
+					   breaking stuff */
+};
+
+#define GSMIOC_GETCONF		_IOR('G', 0, struct gsm_config)
+#define GSMIOC_SETCONF		_IOW('G', 1, struct gsm_config)
+
+
+#endif