GSM Mux in non-transparent mode

These alterations allow the usage of the non-transparent mode of the gsm mux, it works well enough to establish a ppp session using pppd. The increased buffer size allows the usage of the default MRU and MTU sizes in pppd.
Tested with a Telit GE863-Pro^3.

This is my first attempt at a patch so I think it is rather crude, suggestions are welcomed :)

There is a problem that happens if the process that is holding the attached line discipline tries to detach it before a process using a virtual com manages to close it. Both processes end up dealocked. I think this has to do with the tty lock. I don't have the backtrace with me

index aa2e5d3..c244292 100644
@@ -77,8 +77,8 @@ module_param(debug, int, 0600);
  * Semi-arbitary buffer size limits. 0710 is normally run with 32-64

byte
* limits so this is plenty
*/
-#define MAX_MRU 512
-#define MAX_MTU 512
+#define MAX_MRU 2048
+#define MAX_MTU 2048

/*
* Each block of data we have queued to go out is in the form of
@@ -417,6 +417,30 @@ static u8 gsm_encode_modem(const struct gsm_dlci *dlci)
}

/**
+ * gsm_print_modem - Print modem control lines
+ * @dlci: DLCI to encode from
+ *
+ * Print the status of the modem control lines
+ */
+
+static void gsm_print_modem(int mlines)
+{
+ pr_debug("Modem lines: %04X\n", mlines);
+ pr_debug(" RTS:\t%s\n",
+ ((mlines & TIOCM_RTS) == TIOCM_RTS) ? ("ON") : ("OFF"));
+ pr_debug(" CTS:\t%s\n",
+ ((mlines & TIOCM_CTS) == TIOCM_CTS) ? ("ON") : ("OFF"));
+ pr_debug(" DSR:\t%s\n",
+ ((mlines & TIOCM_DSR) == TIOCM_DSR) ? ("ON") : ("OFF"));
+ pr_debug(" DTR:\t%s\n",
+ ((mlines & TIOCM_DTR) == TIOCM_DTR) ? ("ON") : ("OFF"));
+ pr_debug(" DCD:\t%s\n",
+ ((mlines & TIOCM_CD) == TIOCM_CD) ? ("ON") : ("OFF"));
+ pr_debug(" RI :\t%s\n",
+ ((mlines & TIOCM_RI) == TIOCM_RI) ? ("ON") : ("OFF"));
+}
+
+/**
* gsm_print_packet - display a frame for debug
* @hdr: header to print before decode
* @addr: address EA from the frame
@@ -588,7 +612,7 @@ static void gsm_send(struct gsm_mux *gsm, int addr, int cr, int control)
return;
}
gsm->output(gsm, cbuf, len);
- gsm_print_packet("-->", addr, cr, control, NULL, 0);
+ gsm_print_packet("->-", addr, cr, control, NULL, 0);
}

/**
@@ -999,22 +1023,25 @@ static void gsm_control_reply(struct gsm_mux *gsm, int cmd, u8 *data,
static void gsm_process_modem(struct tty_struct *tty, struct gsm_dlci
*dlci,
u32 modem)
{
- int mlines = 0;
+ int mlines = dlci->modem_tx;
u8 brk = modem >> 6;

+ modem = modem >> 1 ;
+
/* Flow control/ready to communicate */
if (modem & MDM_FC) {
+ pr_debug("Flux throttled\n");
/* Need to throttle our output on this device */ dlci->constipated = 1;
}
if (modem & MDM_RTC) {
- mlines |= TIOCM_DSR | TIOCM_DTR;
+ mlines |= TIOCM_DSR ;
dlci->constipated = 0; gsm_dlci_data_kick(dlci);
}
/* Map modem bits */
if (modem & MDM_RTR)
- mlines |= TIOCM_RTS | TIOCM_CTS;
+ mlines |= TIOCM_CTS;
if (modem & MDM_IC)
mlines |= TIOCM_RI;
if (modem & MDM_DV)
@@ -1068,18 +1095,25 @@ static void gsm_control_modem(struct gsm_mux *gsm, u8 *data, int clen)
return;
dlci = gsm->dlci[addr];

- while (gsm_read_ea(&modem, *dp++) == 0) {
- len--;
- if (len == 0)
- return;
+
+ /* Signals frame comes with EA = 0 in GE863-PRO3*/
+ if (len == 1) {
+ modem = *dp ;
+ } else {
+ while (gsm_read_ea(&modem, *dp++) == 0) {
+ len--;
+ if (len == 0)
+ return;
+ }
}
+
tty = tty_port_tty_get(&dlci->port);
gsm_process_modem(tty, dlci, modem);
if (tty) {
tty_wakeup(tty);
tty_kref_put(tty);
}
- gsm_control_reply(gsm, CMD_MSC, data, clen);
+ /*gsm_control_reply(gsm, CMD_MSC, data, clen);*/
}

/**
@@ -1234,6 +1268,10 @@ static void gsm_control_response(struct gsm_mux *gsm, unsigned int command,
/* Rejected by the other end */
if (command == CMD_NSC)
ctrl->error = -EOPNOTSUPP;
+ if (command == CMD_MSC) {
+ /* Out of band modem line change indicator for a DLCI */
+ gsm_control_modem(gsm, data, clen);
+ }
ctrl->done = 1;
wake_up(&gsm->event);
}
@@ -1251,7 +1289,7 @@ static void gsm_control_response(struct gsm_mux *gsm, unsigned int command,
static void gsm_control_transmit(struct gsm_mux *gsm, struct
gsm_control *ctrl)
{
struct gsm_msg *msg = gsm_data_alloc(gsm, 0, ctrl->len + 1,
- gsm->ftype|PF);
+ gsm->ftype/*|PF*/);
if (msg == NULL)
return;
msg->data[0] = (ctrl->cmd << 1) | 2 | EA; /* command */
@@ -1548,6 +1586,7 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, u8 *data, int len)
{
/* See what command is involved */
unsigned int command = 0;
+ pr_debug("%d bytes of command data\n", len);
while (len-- > 0) {
if (gsm_read_ea(&command, *data++) == 1) {
int clen = *data++;
@@ -1555,8 +1594,10 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, u8 *data, int len)
/* FIXME: this is properly an EA */
clen >>= 1;
/* Malformed command ? */
- if (clen > len)
+ if (clen > len) {
+ pr_debug("Malformed Command\n");
return;
+ }
if (command & 1)
gsm_control_message(dlci->gsm, command,
data, clen);
@@ -1673,7 +1714,7 @@ static void gsm_queue(struct gsm_mux *gsm)

cr = gsm->address & 1; /* C/R bit */

- gsm_print_packet("<--", address, cr, gsm->control, gsm->buf,
gsm->len);
+ gsm_print_packet("-<-", address, cr, gsm->control, gsm->buf,
gsm->len);

cr ^= 1 - gsm->initiator; /* Flip so 1 always means command */
dlci = gsm->dlci[address];
@@ -1706,7 +1747,7 @@ static void gsm_queue(struct gsm_mux *gsm)
break;
case UA:
case UA|PF:
- if (cr == 0 || dlci == NULL)
+ if (dlci == NULL)
break;
switch (dlci->state) {
case DLCI_CLOSING:
@@ -2017,6 +2058,9 @@ int gsm_activate_mux(struct gsm_mux *gsm)
dlci = gsm_dlci_alloc(gsm, 0);
if (dlci == NULL)
return -ENOMEM;
+ /* At least Siemens/Cinterion and Telit modems require that the
control
+ channel be open within 5 seconds of starting the cmux mode */
+ gsm_dlci_begin_open(dlci);
gsm->dead = 0; /* Tty opens are now permissible */
return 0;
}
@@ -2093,7 +2137,7 @@ static int gsmld_output(struct gsm_mux *gsm, u8 *data, int len)
return -ENOSPC;
}
if (debug & 4) {
- pr_debug("-->%d bytes out\n", len);
+ pr_debug("%d bytes out\n", len);
hex_packet(data, len);
}
gsm->tty->ops->write(gsm->tty, data, len);
@@ -2150,7 +2194,7 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
char flags;

if (debug & 4) {
- pr_debug("Inbytes %dd\n", count);
+ pr_debug("%d bytes in\n", count);
hex_packet(cp, count);
}

@@ -2508,10 +2552,10 @@ static int gsmtty_modem_update(struct gsm_dlci *dlci, u8 brk)
len++;

modembits[0] = len << 1 | EA; /* Data bytes */
- modembits[1] = dlci->addr << 2 | 3; /* DLCI, EA, 1 */
- modembits[2] = gsm_encode_modem(dlci) << 1 | EA;
+ modembits[1] = (dlci->addr << 2) | 3; /* DLCI, EA, 1 */
+ modembits[2] = gsm_encode_modem(dlci) << 1 /*| EA*/;
if (brk)
- modembits[3] = brk << 4 | 2 | EA; /* Valid, EA */
+ modembits[3] = (brk << 4) | 2 | EA; /* Valid, EA */
ctrl = gsm_control_send(dlci->gsm, CMD_MSC, modembits, len + 1); if (ctrl == NULL)
return -ENOMEM;
@@ -2537,6 +2581,10 @@ static void gsm_dtr_rts(struct tty_port *port, int onoff)
modem_tx |= TIOCM_DTR | TIOCM_RTS;
else
modem_tx &= ~(TIOCM_DTR | TIOCM_RTS);
+
+ if (debug & 16)
+ gsm_print_modem(modem_tx);
+
if (modem_tx != dlci->modem_tx) {
dlci->modem_tx = modem_tx; gsmtty_modem_update(dlci, 0);
@@ -2556,6 +2604,7 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp)
struct tty_port *port;
unsigned int line = tty->index;
unsigned int mux = line >> 6;
+ int ret;

line = line & 0x3F;

@@ -2583,8 +2632,18 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp)
/* We could in theory open and close before we wait - eg if we get
a DM straight back. This is ok as that will have caused a hangup */
set_bit(ASYNCB_INITIALIZED, &port->flags);
+
+ if (debug & 16)
+ pr_debug("Request to open DLCI %d\n", dlci->addr);
+
/* Start sending off SABM messages */ gsm_dlci_begin_open(dlci);
+
+ /* Wait for the modem to send a acknowledge to the open command */
+ ret = wait_event_interruptible(gsm->event, dlci->state == DLCI_OPEN);
+ if (ret < 0)
+ return -ERESTARTSYS;
+
/* And wait for virtual carrier */
return tty_port_block_til_ready(port, tty, filp);
}
@@ -2612,8 +2671,13 @@ static int gsmtty_write(struct tty_struct *tty, const unsigned char *buf,
int len)
{
struct gsm_dlci *dlci = tty->driver_data;
+ int sent;
+
+ if (debug & 16)
+ pr_debug("%d bytes for dlci %d\n", len, dlci->addr);
+
/* Stuff the bytes into the fifo queue */
- int sent = kfifo_in_locked(dlci->fifo, buf, len, &dlci->lock);
+ sent = kfifo_in_locked(dlci->fifo, buf, len, &dlci->lock);
/* Need to kick the channel */
gsm_dlci_data_kick(dlci);
return sent;
@@ -2661,9 +2725,12 @@ static int gsmtty_tiocmset(struct tty_struct *tty, struct file *filp,
struct gsm_dlci *dlci = tty->driver_data;
unsigned int modem_tx = dlci->modem_tx;

- modem_tx &= clear;
+ modem_tx &= ~clear;
modem_tx |= set;

+ if (debug & 16)
+ gsm_print_modem(modem_tx);
+
if (modem_tx != dlci->modem_tx) {
dlci->modem_tx = modem_tx; return gsmtty_modem_update(dlci, 0);

In the tty like adaption layers the buffer size and PPP sizes are not linked, because stuff is diced and packetised. Ok it's probably a performance win. Really it needs network support for best results. There is some prototype code for the network type ones but there are some *horrid* and quite hard to fix races in it that need fixing before that goes upstream

That one is a known recent breakage caused by Arnd's big kernel lock removal. Needs looking at but it looks 'interesting' to fix.

			if (len == 0)
				break;	/* No EA, try what we have*/

here is the log I get here :

[ 1051.950000] ------------[ cut here ]------------
[ 1051.950000] WARNING: at drivers/tty/tty_mutex.c:31 tty_lock+0x30/0x50()
[ 1051.960000] Modules linked in:
[ 1051.960000] [<c0029478>] (unwind_backtrace+0x0/0xe4) from [<c0034f30>] (warn_slowpath_common+0x4c/0x64)
[ 1051.970000] [<c0034f30>] (warn_slowpath_common+0x4c/0x64) from [<c0034f60>] (warn_slowpath_null+0x18/0x1c)
[ 1051.980000] [<c0034f60>] (warn_slowpath_null+0x18/0x1c) from [<c031550c>] (tty_lock+0x30/0x50)
[ 1051.990000] [<c031550c>] (tty_lock+0x30/0x50) from [<c01af5b0>] (__tty_hangup+0x78/0x47c)
[ 1052.000000] [<c01af5b0>] (__tty_hangup+0x78/0x47c) from [<c01ba69c>] (gsm_cleanup_mux+0x198/0x214)
[ 1052.010000] [<c01ba69c>] (gsm_cleanup_mux+0x198/0x214) from [<c01baaf4>] (gsmld_close+0x28/0x4c)
[ 1052.020000] [<c01baaf4>] (gsmld_close+0x28/0x4c) from [<c01b5974>] (tty_ldisc_close+0x58/0x64)
[ 1052.030000] [<c01b5974>] (tty_ldisc_close+0x58/0x64) from [<c01b5b48>] (tty_ldisc_release+0x38/0x70)
[ 1052.040000] [<c01b5b48>] (tty_ldisc_release+0x38/0x70) from [<c01b0e2c>] (tty_release+0x41c/0x480)
[ 1052.050000] [<c01b0e2c>] (tty_release+0x41c/0x480) from [<c009667c>] (fput+0x108/0x200)
[ 1052.060000] [<c009667c>] (fput+0x108/0x200) from [<c00939c8>] (filp_close+0x60/0x6c)
[ 1052.070000] [<c00939c8>] (filp_close+0x60/0x6c) from [<c0036eb8>] (put_files_struct+0x80/0xdc)
[ 1052.080000] [<c0036eb8>] (put_files_struct+0x80/0xdc) from [<c0038500>] (do_exit+0x1b8/0x6bc)
[ 1052.080000] [<c0038500>] (do_exit+0x1b8/0x6bc) from [<c0038ac4>] (do_group_exit+0xc0/0xf4)
[ 1052.090000] [<c0038ac4>] (do_group_exit+0xc0/0xf4) from [<c0044460>] (get_signal_to_deliver+0x3ac/0x40c)
[ 1052.100000] [<c0044460>] (get_signal_to_deliver+0x3ac/0x40c) from [<c0027190>] (do_signal+0x68/0x614)
[ 1052.110000] [<c0027190>] (do_signal+0x68/0x614) from [<c0027754>] (do_notify_resume+0x18/0x60)
[ 1052.120000] [<c0027754>] (do_notify_resume+0x18/0x60) from [<c0024f94>] (work_pending+0x24/0x28)
[ 1052.130000] ---[ end trace ac06c34c1914deef ]---

Eric

Hi,

Thank you for your comments. I think the biggest problem with what I did was forget that the driver should also work as a modem end, I'll recheck my changes using your suggestions and try to submit the new patches soon.

I've retested it with the 512 limits and it sometimes works. I'm not sure where the problem is as it wasn't me that configured the ppp server, but I will see if I can track down the real problem. Bigger limits on the buffer seems to work better but it can be bias on my part.

This is just because the string '<--' seems to get eaten by a printk somewhere, so I changed it to '-<-', that change is just to be consistent but it's not very important.

I definitely like your solution better. If I read the standard correctly EA should be set to 1 if there is no break octet. However this is what happens:

OUT: F9 03 EF 09 E3 05 07 0D FB F9
IN:  F9 03 EF 09 E1 05 07 0C FB F9

I think it's a bug on the modem, but I can be reading the standard wrong, have to try with a modem from another manufacturer and check what happens.

I will think a bit more about how to do this. I should have considered what happens if the driver is behaving as the modem.

My mistake, now that I think back I can't find the reason for why I did this. :)

I hadn't noticed that doing a GSMIOC_SETCONF fires a DLCI 0 open command, oops.

My idea was to wait for the acknowledge to the SAMB message before firing the MSC, but if this is wrong I think its better to leave it out. At least the GE863-Pro^3 seems to reply to the SAMB with the acknowledge and an MSC independently if we asked for it or not.

Hi Mário,

Hi Eric
My GE863-Pro^3 works well without it, however, without it the control signals from the computer side do not seem to work correctly.

change when we send TIOCMSET commands.

By the way, can you confirm if your Telit modems respect the EA bit on the MSC frame ?

Thank you,

Mário Isidoro

Hi Mário,

here without this fix, ppp gets blocked during init.

I get the exact same byte sequence as you do.

Eric