n_gsm : Flow control handling in Mux driver

- 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@intel.com>
Signed-off-by: Russ Gorby <russ.gorby@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c028f35702469cdb1735f0b4eb54d09fbbc82269..db15b562a29e7c864b7c0b867875908d2a13c401 100644 (file)
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -673,6 +673,8 @@ static struct gsm_msg *gsm_data_alloc(struct gsm_mux *gsm, u8 addr, int len,
  *
  *     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(struct gsm_mux *gsm, u8 addr, int len,
 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 *gsm)
                                                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_dlci *dlci, struct gsm_msg *msg)
        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)
@@ -944,6 +956,9 @@ static void gsm_dlci_data_sweep(struct gsm_mux *gsm)
                        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;
                }
@@ -973,6 +988,13 @@ static void gsm_dlci_data_kick(struct gsm_dlci *dlci)
        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);
@@ -1030,6 +1052,7 @@ static void gsm_process_modem(struct tty_struct *tty, struct gsm_dlci *dlci,
 {
        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
@@ -1041,19 +1064,27 @@ static void gsm_process_modem(struct tty_struct *tty, struct gsm_dlci *dlci,
        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)
@@ -1209,17 +1240,21 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
                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 */
                gsm_data_kick(gsm);
                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);
@@ -2276,7 +2311,7 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
                        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;
                }