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greybus: timesync: Implement a retry mechanism

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It's possible the AP could miss an incoming SVC timesync pulse i.e. the AP
could have interrupts switched off for long enough that one SVC GPIO strobe
ends up over-lapping another one. TimeSync should be able to deal with this
type of transitory failure by retrying a failed synchronous TimeSync resync
up to 'n' number of times. For this patch 'n' has been set to five, which
is a hand-wavy choice that 'feels' right.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Bryan O'Donoghue 2016-08-02 13:18:30 +01:00 committed by Greg Kroah-Hartman
parent b6fc2876a0
commit 7aa278b771
1 changed files with 16 additions and 6 deletions
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22
drivers/staging/greybus/timesync.c
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@ -34,6 +34,9 @@
#define GB_TIMESYNC_KTIME_UPDATE msecs_to_jiffies(1000)
#define GB_TIMESYNC_MAX_KTIME_CONVERSION 15
/* Maximum number of times we'll retry a failed synchronous sync */
#define GB_TIMESYNC_MAX_RETRIES 5
/* Reported nanoseconds/femtoseconds per clock */
static u64 gb_timesync_ns_per_clock;
static u64 gb_timesync_fs_per_clock;
@ -870,19 +873,26 @@ int gb_timesync_schedule_synchronous(struct gb_interface *interface)
{
int ret;
struct gb_timesync_svc *timesync_svc;
int retries;
if (!(interface->features & GREYBUS_INTERFACE_FEATURE_TIMESYNC))
return 0;
mutex_lock(&gb_timesync_svc_list_mutex);
timesync_svc = gb_timesync_find_timesync_svc(interface->hd);
if (!timesync_svc) {
ret = -ENODEV;
goto done;
}
for (retries = 0; retries < GB_TIMESYNC_MAX_RETRIES; retries++) {
timesync_svc = gb_timesync_find_timesync_svc(interface->hd);
if (!timesync_svc) {
ret = -ENODEV;
goto done;
}
ret = __gb_timesync_schedule_synchronous(timesync_svc,
ret = __gb_timesync_schedule_synchronous(timesync_svc,
GB_TIMESYNC_STATE_INIT);
if (!ret)
break;
}
if (ret && retries == GB_TIMESYNC_MAX_RETRIES)
ret = -ETIMEDOUT;
done:
mutex_unlock(&gb_timesync_svc_list_mutex);
return ret;