From e9ec22547986dd32c5c70da78107ce35dbff1344 Mon Sep 17 00:00:00 2001 From: Tony Lindgren Date: Sat, 7 Apr 2018 10:19:50 -0700 Subject: tty: n_gsm: Fix long delays with control frame timeouts in ADM mode 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 Cc: Dan Williams Cc: Jiri Prchal Cc: Jiri Slaby Cc: Marcel Partap Cc: Merlijn Wajer Cc: Michael Nazzareno Trimarchi Cc: Michael Scott Cc: Pavel Machek Cc: Peter Hurley Cc: Russ Gorby Cc: Sascha Hauer Cc: Sebastian Reichel Signed-off-by: Tony Lindgren Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_gsm.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'drivers/tty') diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 3b3e1f6632d7..7b1f8636f8e9 100644 --- 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_list *t) 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); -- cgit v1.2.3