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tty: n_gsm: add ioctl to map serial device to mux'ed tty

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Guessing the first tty for a gsm0710 multiplexed serial device is not
currently possible, which makes it racy to use with multiple modems.

Add a way to map the physical serial tty to its related mux devices
using an ioctl.

Signed-off-by: Martin Hundebøll <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Martin Hundebøll 2019-08-12 23:12:43 +02:00 • committed by Greg Kroah-Hartman
commit a7b121b4b8
3 changed files with 15 additions and 2 deletions
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11
Documentation/driver-api/serial/n_gsm.rst
View file

@ -18,10 +18,13 @@ How to use it
2. switch the serial line to using the n_gsm line discipline by using
TIOCSETD ioctl,
3. configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
4. obtain base gsmtty number for the used serial port,
Major parts of the initialization program :
(a good starting point is util-linux-ng/sys-utils/ldattach.c)::
#include <stdio.h>
#include <stdint.h>
#include <linux/gsmmux.h>
#include <linux/tty.h>
#define DEFAULT_SPEED B115200
@ -30,6 +33,7 @@ Major parts of the initialization program :
int ldisc = N_GSM0710;
struct gsm_config c;
struct termios configuration;
uint32_t first;
/* open the serial port connected to the modem */
fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
@ -58,19 +62,22 @@ Major parts of the initialization program :
c.mtu = 127;
/* set the new configuration */
ioctl(fd, GSMIOC_SETCONF, &c);
/* get first gsmtty device node */
ioctl(fd, GSMIOC_GETFIRST, &first);
printf("first muxed line: /dev/gsmtty%i\n", first);
/* and wait for ever to keep the line discipline enabled */
daemon(0,0);
pause();
4. use these devices as plain serial ports.
5. use these devices as plain serial ports.
for example, it's possible:
- and to use gnokii to send / receive SMS on ttygsm1
- to use ppp to establish a datalink on ttygsm2
5. first close all virtual ports before closing the physical port.
6. first close all virtual ports before closing the physical port.
Note that after closing the physical port the modem is still in multiplexing
mode. This may prevent a successful re-opening of the port later. To avoid