[PATCH 3.4 134/214] n_gsm : Flow control handling in Mux driver

From: Greg Kroah-Hartman
Date: Thu Jun 05 2014 - 00:43:01 EST

3.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Frederic Berat <fredericx.berat@xxxxxxxxx>

commit c01af4fec2c8f303d6b3354d44308d9e6bef8026 upstream.

- Correcting handling of FCon/FCoff in order to respect 27.010 spec
- Consider FCon/off will overide all dlci flow control except for
dlci0 as we must be able to send control frames.
- Dlci constipated handling according to FC, RTC and RTR values.
- Modifying gsm_dlci_data_kick and gsm_dlci_data_sweep according
to dlci constipated value

Signed-off-by: Frederic Berat <fredericx.berat@xxxxxxxxx>
Signed-off-by: Russ Gorby <russ.gorby@xxxxxxxxx>
Signed-off-by: Alan Cox <alan@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Cc: Rui Xiang <rui.xiang@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/tty/n_gsm.c | 79 +++++++++++++++++++++++++++++++++++++---------------
1 file changed, 57 insertions(+), 22 deletions(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -673,6 +673,8 @@ static struct gsm_msg *gsm_data_alloc(st
*
* The tty device has called us to indicate that room has appeared in
* the transmit queue. Ram more data into the pipe if we have any
+ * If we have been flow-stopped by a CMD_FCOFF, then we can only
+ * send messages on DLCI0 until CMD_FCON
*
* FIXME: lock against link layer control transmissions
*/
@@ -680,15 +682,19 @@ static struct gsm_msg *gsm_data_alloc(st
static void gsm_data_kick(struct gsm_mux *gsm)
{
struct gsm_msg *msg = gsm->tx_head;
+ struct gsm_msg *free_msg;
int len;
int skip_sof = 0;

- /* FIXME: We need to apply this solely to data messages */
- if (gsm->constipated)
- return;
-
- while (gsm->tx_head != NULL) {
- msg = gsm->tx_head;
+ while (msg) {
+ if (gsm->constipated && msg->addr) {
+ msg = msg->next;
+ continue;
+ }
+ if (gsm->dlci[msg->addr]->constipated) {
+ msg = msg->next;
+ continue;
+ }
if (gsm->encoding != 0) {
gsm->txframe[0] = GSM1_SOF;
len = gsm_stuff_frame(msg->data,
@@ -711,15 +717,19 @@ static void gsm_data_kick(struct gsm_mux
len - skip_sof) < 0)
break;
/* FIXME: Can eliminate one SOF in many more cases */
- gsm->tx_head = msg->next;
- if (gsm->tx_head == NULL)
- gsm->tx_tail = NULL;
gsm->tx_bytes -= msg->len;
- kfree(msg);
/* For a burst of frames skip the extra SOF within the
burst */
skip_sof = 1;
+
+ if (gsm->tx_head == msg)
+ gsm->tx_head = msg->next;
+ free_msg = msg;
+ msg = msg->next;
+ kfree(free_msg);
}
+ if (!gsm->tx_head)
+ gsm->tx_tail = NULL;
}

/**
@@ -738,6 +748,8 @@ static void __gsm_data_queue(struct gsm_
u8 *dp = msg->data;
u8 *fcs = dp + msg->len;

+ WARN_ONCE(dlci->constipated, "%s: queueing from a constipated DLCI",
+ __func__);
/* Fill in the header */
if (gsm->encoding == 0) {
if (msg->len < 128)
@@ -947,6 +959,9 @@ static void gsm_dlci_data_sweep(struct g
break;
dlci = gsm->dlci[i];
if (dlci == NULL || dlci->constipated) {
+ if (dlci && (debug & 0x20))
+ pr_info("%s: DLCI %d is constipated",
+ __func__, i);
i++;
continue;
}
@@ -976,6 +991,13 @@ static void gsm_dlci_data_kick(struct gs
unsigned long flags;
int sweep;

+ if (dlci->constipated) {
+ if (debug & 0x20)
+ pr_info("%s: DLCI %d is constipated",
+ __func__, dlci->addr);
+ return;
+ }
+
spin_lock_irqsave(&dlci->gsm->tx_lock, flags);
/* If we have nothing running then we need to fire up */
sweep = (dlci->gsm->tx_bytes < TX_THRESH_LO);
@@ -1033,6 +1055,7 @@ static void gsm_process_modem(struct tty
{
int mlines = 0;
u8 brk = 0;
+ int fc;

/* The modem status command can either contain one octet (v.24 signals)
or two octets (v.24 signals + break signals). The length field will
@@ -1044,19 +1067,27 @@ static void gsm_process_modem(struct tty
else {
brk = modem & 0x7f;
modem = (modem >> 7) & 0x7f;
- };
+ }

/* Flow control/ready to communicate */
- if (modem & MDM_FC) {
+ fc = (modem & MDM_FC) || !(modem & MDM_RTR);
+ if (fc && !dlci->constipated) {
+ if (debug & 0x20)
+ pr_info("%s: DLCI %d START constipated (tx_bytes=%d)",
+ __func__, dlci->addr, dlci->gsm->tx_bytes);
/* Need to throttle our output on this device */
dlci->constipated = 1;
- }
- if (modem & MDM_RTC) {
- mlines |= TIOCM_DSR | TIOCM_DTR;
+ } else if (!fc && dlci->constipated) {
+ if (debug & 0x20)
+ pr_info("%s: DLCI %d END constipated (tx_bytes=%d)",
+ __func__, dlci->addr, dlci->gsm->tx_bytes);
dlci->constipated = 0;
gsm_dlci_data_kick(dlci);
}
+
/* Map modem bits */
+ if (modem & MDM_RTC)
+ mlines |= TIOCM_DSR | TIOCM_DTR;
if (modem & MDM_RTR)
mlines |= TIOCM_RTS | TIOCM_CTS;
if (modem & MDM_IC)
@@ -1225,19 +1256,23 @@ static void gsm_control_message(struct g
gsm_control_reply(gsm, CMD_TEST, data, clen);
break;
case CMD_FCON:
- /* Modem wants us to STFU */
- gsm->constipated = 1;
- gsm_control_reply(gsm, CMD_FCON, NULL, 0);
- break;
- case CMD_FCOFF:
/* Modem can accept data again */
+ if (debug & 0x20)
+ pr_info("%s: GSM END constipation", __func__);
gsm->constipated = 0;
- gsm_control_reply(gsm, CMD_FCOFF, NULL, 0);
+ gsm_control_reply(gsm, CMD_FCON, NULL, 0);
/* Kick the link in case it is idling */
spin_lock_irqsave(&gsm->tx_lock, flags);
gsm_data_kick(gsm);
spin_unlock_irqrestore(&gsm->tx_lock, flags);
break;
+ case CMD_FCOFF:
+ /* Modem wants us to STFU */
+ if (debug & 0x20)
+ pr_info("%s: GSM START constipation", __func__);
+ gsm->constipated = 1;
+ gsm_control_reply(gsm, CMD_FCOFF, NULL, 0);
+ break;
case CMD_MSC:
/* Out of band modem line change indicator for a DLCI */
gsm_control_modem(gsm, data, clen);
@@ -2306,7 +2341,7 @@ static void gsmld_receive_buf(struct tty
gsm->error(gsm, *dp, flags);
break;
default:
- WARN_ONCE("%s: unknown flag %d\n",
+ WARN_ONCE(1, "%s: unknown flag %d\n",
tty_name(tty, buf), flags);
break;
}


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