charger: Add delay in tasker task to avoid lockup

The charger task relies on calc_next_state() performing a delay before
returning. My reading of the code suggests that this doesn't happen
always. For example:

When pre-charging:

		if (battery_temperature(&batt_temp) == EC_SUCCESS)
			return ST_CHARGING;

When discharging and capacity is low:

		/* Check remaining charge % */
		if (battery_state_of_charge(&capacity) == 0 && capacity < 10)
			return notify_battery_low();

I would like to suggest that the code be refactored to more like:

int next_checkms = 5000;  /* next time to check battery */

while (1) {
    int action = ACTION_NONE;

	err = get_state(&state);
	if (!err) {
	   action = calculate_action(&state);
	   err = perform_action(action, &next_check_ms);
    }

	usleep(next_check_ms * 1000);
}

so that the delays are really clear, the state is all read at once,
there is no reliance on earlier state, and we always delay even on
error.

In the meantime, this CL inserts a mandatory 5 second delay in the
loop, which should prevent the charger task lockup.

BUG=chrome-os-partner:11285
TEST=manual
(please do this test before committing)
1. boot to kernel, see that battery can be seen
2. suspend and resume device
3. see that the charger loop does not cause an EC watchdog reset and
AP power off/reset. There should be no watchdog warning message on the
EC console.

Change-Id: I141e374933c4dc0ec60bcdccf96443f57067c585
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/27353
Reviewed-by: Rong Chang <rongchang@chromium.org>
Tested-by: Rong Chang <rongchang@chromium.org>
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>
Tested-by: Katie Roberts-Hoffman <katierh@chromium.org>
Commit-Ready: Katie Roberts-Hoffman <katierh@chromium.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/common/pmu_tps65090_charger.c b/common/pmu_tps65090_charger.c
index b4b1c05fbc..4aacf99155 100644
--- a/common/pmu_tps65090_charger.c
+++ b/common/pmu_tps65090_charger.c
@@ -296,5 +296,8 @@ void pmu_charger_task(void)
 				state_list[next_state]);
 			state = next_state;
 		}
+
+		/* TODO(sjg@chromium.org): root cause crosbug.com/p/11285 */
+		usleep(5000 * 1000);
 	}
 }