tty: n_gsm: Fix control dlci ADM mode processing

Currently, code retries n2 times to open control dlci in ABM mode before
switching to ADM mode, but only if DM has been received. This contradicts
to the comment that dlci is switched to control mode unconditionally if
DLCI_OPENING retries time out. Also, it does not make sense to continue
trying once DM has received.

Change the logic to switch to ADM mode upon DM received. That way control
channel state will change to DLCI_OPEN way faster. Fix the misleading
comment while at it.

Signed-off-by: Ivaylo Dimitrov <[email protected]>
Signed-off-by: Tony Lindgren <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: freemangordon

drivers/tty/n_gsm.c

@@ -2224,7 +2224,7 @@ static int gsm_dlci_negotiate(struct gsm_dlci *dlci)
  *
  *	Some control dlci can stay in ADM mode with other dlci working just
  *	fine. In that case we can just keep the control dlci open after the
- *	DLCI_OPENING retries time out.
+ *	DLCI_OPENING receives DM.
  */
 
 static void gsm_dlci_t1(struct timer_list *t)
@@ -2243,19 +2243,19 @@ static void gsm_dlci_t1(struct timer_list *t)
 		}
 		break;
 	case DLCI_OPENING:
-		if (dlci->retries) {
+		if (!dlci->addr && gsm->control == (DM | PF)) {
+			if (debug & DBG_ERRORS)
+				pr_info("DLCI 0 opening in ADM mode.\n");
+			dlci->mode = DLCI_MODE_ADM;
+			gsm_dlci_open(dlci);
+		} else if (dlci->retries) {
 			if (!dlci->addr || !gsm->dlci[0] ||
 			    gsm->dlci[0]->state != DLCI_OPENING) {
 				dlci->retries--;
 				gsm_command(dlci->gsm, dlci->addr, SABM|PF);
 			}
 
 			mod_timer(&dlci->t1, jiffies + gsm->t1 * HZ / 100);
-		} else if (!dlci->addr && gsm->control == (DM | PF)) {
-			if (debug & DBG_ERRORS)
-				pr_info("DLCI 0 opening in ADM mode.\n");
-			dlci->mode = DLCI_MODE_ADM;
-			gsm_dlci_open(dlci);
 		} else {
 			gsm->open_error++;
 			gsm_dlci_begin_close(dlci); /* prevent half open link */