3.18-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 @@ -137,6 +137,9 @@ 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; @@ -1380,7 +1383,13 @@ 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); @@ -1488,6 +1497,7 @@ static void gsm_dlci_t1(unsigned long da 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);