[PATCH 4.16 032/113] tty: n_gsm: Fix long delays with control frame timeouts in ADM mode

[PATCH 4.16 032/113] tty: n_gsm: Fix long delays with control frame timeouts in ADM mode

[Greg Kroah-Hartman]

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

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

From: Tony Lindgren <tony@atomide.com>

commit e9ec22547986dd32c5c70da78107ce35dbff1344 upstream.

Commit ea3d8465ab9b ("tty: n_gsm: Allow ADM response in addition to UA for
control dlci") added support for DLCI to stay in Asynchronous Disconnected
Mode (ADM). But we still get long delays waiting for commands to other
DLCI to complete:

--> 5) C: SABM(P)
Q>  0) C: UIH(F)
Q>  0) C: UIH(F)
Q>  0) C: UIH(F)
...

This happens because gsm_control_send() sets cretries timer to T2 that is
by default set to 34. This will cause resend for T2 times for the control
frame. In ADM mode, we will never get a response so the control frame, so
retries are just delaying all the commands.

Let's fix the issue by setting DLCI_MODE_ADM flag after detecting the ADM
mode for the control DLCI. Then we can use that in gsm_control_send() to
set retries to 1. This means the control frame will be sent once allowing
the other end at an opportunity to switch from ADM to ABM mode.

Note that retries will be decremented in gsm_control_retransmit() so
we don't want to set it to 0 here.

Fixes: ea3d8465ab9b ("tty: n_gsm: Allow ADM response in addition to UA for control dlci")
Cc: linux-serial@vger.kernel.org
Cc: Alan Cox <alan@llwyncelyn.cymru>
Cc: Dan Williams <dcbw@redhat.com>
Cc: Jiri Prchal <jiri.prchal@aksignal.cz>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
Cc: Michael Scott <michael.scott@linaro.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Russ Gorby <russ.gorby@intel.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/n_gsm.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -121,6 +121,9 @@ struct gsm_dlci {
 	struct mutex mutex;
 
 	/* Link layer */
+	int mode;
+#define DLCI_MODE_ABM		0	/* Normal Asynchronous Balanced Mode */
+#define DLCI_MODE_ADM		1	/* Asynchronous Disconnected Mode */
 	spinlock_t lock;	/* Protects the internal state */
 	struct timer_list t1;	/* Retransmit timer for SABM and UA */
 	int retries;
@@ -1364,7 +1367,13 @@ retry:
 	ctrl->data = data;
 	ctrl->len = clen;
 	gsm->pending_cmd = ctrl;
-	gsm->cretries = gsm->n2;
+
+	/* If DLCI0 is in ADM mode skip retries, it won't respond */
+	if (gsm->dlci[0]->mode == DLCI_MODE_ADM)
+		gsm->cretries = 1;
+	else
+		gsm->cretries = gsm->n2;
+
 	mod_timer(&gsm->t2_timer, jiffies + gsm->t2 * HZ / 100);
 	gsm_control_transmit(gsm, ctrl);
 	spin_unlock_irqrestore(&gsm->control_lock, flags);
@@ -1472,6 +1481,7 @@ static void gsm_dlci_t1(struct timer_lis
 			if (debug & 8)
 				pr_info("DLCI %d opening in ADM mode.\n",
 					dlci->addr);
+			dlci->mode = DLCI_MODE_ADM;
 			gsm_dlci_open(dlci);
 		} else {
 			gsm_dlci_close(dlci);

[PATCH 4.16 033/113] tty: n_gsm: Fix DLCI handling for ADM mode if debug & 2 is not set

[Greg Kroah-Hartman]

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

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

From: Tony Lindgren <tony@atomide.com>

commit b2d89ad9c9682e795ed6eeb9ed455789ad6cedf1 upstream.

At least on droid 4 with control channel in ADM mode, there is no response
to Modem Status Command (MSC). Currently gsmtty_modem_update() expects to
have data in dlci->modem_rx unless debug & 2 is set. This means that on
droid 4, things only work if debug & 2 is set.

Let's fix the issue by ignoring empty dlci->modem_rx for ADM mode. In
the AMD mode, CMD_MSC will never respond and gsm_process_modem() won't
get called to set dlci->modem_rx.

And according to ts_127010v140000p.pdf, MSC is only relevant if basic
option is chosen, so let's test for that too.

Fixes: ea3d8465ab9b ("tty: n_gsm: Allow ADM response in addition to UA for control dlci")
Cc: linux-serial@vger.kernel.org
Cc: Alan Cox <alan@llwyncelyn.cymru>
Cc: Dan Williams <dcbw@redhat.com>
Cc: Jiri Prchal <jiri.prchal@aksignal.cz>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
Cc: Michael Scott <michael.scott@linaro.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Russ Gorby <russ.gorby@intel.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/n_gsm.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2871,11 +2871,22 @@ static int gsmtty_modem_update(struct gs
 static int gsm_carrier_raised(struct tty_port *port)
 {
 	struct gsm_dlci *dlci = container_of(port, struct gsm_dlci, port);
+	struct gsm_mux *gsm = dlci->gsm;
+
 	/* Not yet open so no carrier info */
 	if (dlci->state != DLCI_OPEN)
 		return 0;
 	if (debug & 2)
 		return 1;
+
+	/*
+	 * Basic mode with control channel in ADM mode may not respond
+	 * to CMD_MSC at all and modem_rx is empty.
+	 */
+	if (gsm->encoding == 0 && gsm->dlci[0]->mode == DLCI_MODE_ADM &&
+	    !dlci->modem_rx)
+		return 1;
+
 	return dlci->modem_rx & TIOCM_CD;
 }