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drivers: modem: gsm_ppp: proper attach retry

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In a previous commit, a check was added to ensure modem was properly
attached to packet service before initializing PPP. Failure to perform
this check can lead to the dreaded 'NO CARRIER' issue.

While this is a nice idea, the implementation was lacking because when
the check failed, the entire modem initialization procedure was
restarted from square one. For modems/bearers that were slow to attach,
this is potentially disastrous. The proper solution is to loop only the
'AT+CGATT?' part until it succeeds, or fails N times.

This commit implements this looping behavior (using the work queue).

Signed-off-by: Benjamin Lindqvist <benjamin.lindqvist@endian.se>
This commit is contained in:
Benjamin Lindqvist 2020-12-10 11:38:43 +01:00 • committed by Jukka Rissanen
commit 28ac1f70bf
2 changed files with 38 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

8
drivers/modem/Kconfig.gsm
View file

@ -62,6 +62,14 @@ config GSM_PPP_AUTOSTART
modem connects to network. See contents of "drivers/gsm_ppp.h"
to get an idea of the API.
config MODEM_GSM_ATTACH_TIMEOUT
int "Timeout for attaching to packet service"
default 30
help
Before activating PPP, attachment to packet service is checked
using AT+CGATT. This setting dictates how much time in seconds
we give the modem before giving up.
config MODEM_GSM_MANUAL_MCCMNO
string "MCC/MNO for establishing network connection"
help

25
drivers/modem/gsm_ppp.c
View file

@ -28,6 +28,8 @@ LOG_MODULE_REGISTER(modem_gsm, CONFIG_MODEM_LOG_LEVEL);
#define GSM_RX_STACK_SIZE CONFIG_MODEM_GSM_RX_STACK_SIZE
#define GSM_RECV_MAX_BUF 30
#define GSM_RECV_BUF_SIZE 128
#define GSM_ATTACH_RETRY_DELAY_MSEC 1000
/* During the modem setup, we first create DLCI control channel and then
* PPP and AT channels. Currently the modem does not create possible GNSS
@ -62,6 +64,7 @@ static struct gsm_modem {
struct net_if *iface;
int attach_retries;
bool mux_enabled : 1;
bool mux_setup_done : 1;
bool setup_done : 1;
@ -350,6 +353,11 @@ static void gsm_finalize_connection(struct gsm_modem *gsm)
{
int ret;
/* If attach check failed, we should not redo every setup step */
if (gsm->attach_retries) {
goto attaching;
}
if (IS_ENABLED(CONFIG_GSM_MUX) && gsm->mux_enabled) {
ret = modem_cmd_send_nolock(&gsm->context.iface,
&gsm->context.cmd_handler,
@ -392,6 +400,7 @@ static void gsm_finalize_connection(struct gsm_modem *gsm)
return;
}
attaching:
/* Don't initialize PPP until we're attached to packet service */
ret = modem_cmd_send_nolock(&gsm->context.iface,
&gsm->context.cmd_handler,
@ -400,12 +409,26 @@ static void gsm_finalize_connection(struct gsm_modem *gsm)
&gsm->sem_response,
GSM_CMD_SETUP_TIMEOUT);
if (ret < 0) {
/*
* attach_retries not set -> trigger N attach retries
* attach_retries set -> decrement and retry
* attach_retries set, becomes 0 -> trigger full retry
*/
if (!gsm->attach_retries) {
gsm->attach_retries = CONFIG_MODEM_GSM_ATTACH_TIMEOUT *
MSEC_PER_SEC / GSM_ATTACH_RETRY_DELAY_MSEC;
} else {
gsm->attach_retries--;
}
LOG_DBG("Not attached, %s", "retrying...");
(void)k_delayed_work_submit(&gsm->gsm_configure_work,
K_SECONDS(1));
K_MSEC(GSM_ATTACH_RETRY_DELAY_MSEC));
return;
}
/* Attached, clear retry counter */
gsm->attach_retries = 0;
LOG_DBG("modem setup returned %d, %s", ret, "enable PPP");