ab8500-btemp: Filter btemp readings

Battery tempreature readings sometimes fail and results in
a value far from recent values. This patch adds a software
filter that disposes such readings, by allowing direct
updates on temperature only if two samples result in the
same temperature. Else only allow 1 degree change from previous
reported value in the direction of the new measurement.

Signed-off-by: Hakan Berg <hakan.berg@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Marcus COOPER <marcus.xm.cooper@stericsson.com>
Reviewed-by: Martin SJOBLOM <martin.w.sjoblom@stericsson.com>
Reviewed-by: Rabin VINCENT <rabin.vincent@stericsson.com>

1 files changed, 21 insertions, 6 deletions

diff --git a/drivers/power/ab8500_btemp.c b/drivers/power/ab8500_btemp.c
index 07689064996e..fa60e3ac33a3 100644
--- a/drivers/power/ab8500_btemp.c
+++ b/drivers/power/ab8500_btemp.c
@@ -76,8 +76,8 @@ struct ab8500_btemp_ranges {
  * @dev:                Pointer to the structure device
  * @node:               List of AB8500 BTEMPs, hence prepared for reentrance
  * @curr_source:        What current source we use, in uA
- * @bat_temp:           Battery temperature in degree Celcius
- * @prev_bat_temp       Last dispatched battery temperature
+ * @bat_temp:           Dispatched battery temperature in degree Celcius
+ * @prev_bat_temp       Last measured battery temperature in degree Celcius
  * @parent:             Pointer to the struct ab8500
  * @gpadc:              Pointer to the struct gpadc
  * @fg:                 Pointer to the struct fg
@@ -604,6 +604,7 @@ static int ab8500_btemp_id(struct ab8500_btemp *di)
 static void ab8500_btemp_periodic_work(struct work_struct *work)
 {
         int interval;
+        int bat_temp;
         struct ab8500_btemp *di = container_of(work,
                 struct ab8500_btemp, btemp_periodic_work.work);
 
@@ -614,12 +615,26 @@ static void ab8500_btemp_periodic_work(struct work_struct *work)
                         dev_warn(di->dev, "failed to identify the battery\n");
         }
 
-        di->bat_temp = ab8500_btemp_measure_temp(di);
-
-        if (di->bat_temp != di->prev_bat_temp) {
-                di->prev_bat_temp = di->bat_temp;
+        bat_temp = ab8500_btemp_measure_temp(di);
+        /*
+         * Filter battery temperature.
+         * Allow direct updates on temperature only if two samples result in
+         * same temperature. Else only allow 1 degree change from previous
+         * reported value in the direction of the new measurement.
+         */
+        if (bat_temp == di->prev_bat_temp || !di->initialized) {
+                if (di->bat_temp != di->prev_bat_temp || !di->initialized) {
+                        di->bat_temp = bat_temp;
+                        power_supply_changed(&di->btemp_psy);
+                }
+        } else if (bat_temp < di->prev_bat_temp) {
+                di->bat_temp--;
+                power_supply_changed(&di->btemp_psy);
+        } else if (bat_temp > di->prev_bat_temp) {
+                di->bat_temp++;
                 power_supply_changed(&di->btemp_psy);
         }
+        di->prev_bat_temp = bat_temp;
 
         if (di->events.ac_conn || di->events.usb_conn)
                 interval = di->bm->temp_interval_chg;