libsensors: fix sensors enable and disable

    * "//Accel sensor is first on and last off"

      This is totally wrong. The since we are using a single sysfs path
      to enable and disable all of the sensors, the kernel driver uses
      bitwise operations on the input value to know which sensors should
      be enabled. The current logic wrongly assumes that the sensors are
      enabled and disabled in a specific order and if accelerometer was
      disabled, all of the other sensors were being disabled too. This
      caused inconsistent sensor states between the sensor HAL and the
      kernel driver and most of the time, the sensors failed to work
      properly and drained battery.

      Simplify the code to use bitwise operations instead of arithematic
      operations to keep things clean. Additionally, since two or more
      sensors can be enabled or disabled at the same time, we use a lock
      to prevent race conditions.

Change-Id: Ifc3fab1456d4061f58d52f2ecda822c6157aae6e

1 files changed, 16 insertions, 24 deletions

diff --git a/libsensors/SensorBase.cpp b/libsensors/SensorBase.cpp
index 9c27184..1a25c96 100644
--- a/libsensors/SensorBase.cpp
+++ b/libsensors/SensorBase.cpp
@@ -21,6 +21,7 @@
 #include <unistd.h>
 #include <dirent.h>
 #include <sys/select.h>
+#include <pthread.h>
 
 #include <cutils/log.h>
 
@@ -30,6 +31,8 @@
 
 /*****************************************************************************/
 
+static pthread_mutex_t sspEnableLock = PTHREAD_MUTEX_INITIALIZER;
+
 SensorBase::SensorBase(
         const char* dev_name,
         const char* data_name)
@@ -141,34 +144,23 @@ int SensorBase::flush(int handle)
 int SensorBase::sspEnable(const char* sensorname, int sensorvalue, int en)
 {
     FILE* sspfile;
-    int oldvalue = 0;
-    int reset = 0;
-    int newvalue;
-    int fd;
+    int sspValue = 0;
+
+    pthread_mutex_lock(&sspEnableLock);
 
     sspfile = fopen(SSP_DEVICE_ENABLE, "r+");
-    fscanf(sspfile, "%d", &oldvalue);
+    fscanf(sspfile, "%d", &sspValue);
     fclose(sspfile);
 
-//Accel sensor is first on and last off, if we are disabling it
-// assume the screen is off, disable all sensors and zero everything out
-// to keep enable file in sync.
-    if(sensorvalue == SSP_ACCEL && !en) {
-        //ALOGD("SensorBase: Resetting sensors");
-        for(int i; i < 6; i++){
-	  newvalue = oldvalue - ssp_sensors[i];
-	  //ALOGD("SensorBase: newvalue: %i ",newvalue);
-	  sspWrite(newvalue);
-	}
-        sspWrite('\0');
-	return 0;
-    } else if(en) {
-        newvalue = oldvalue + sensorvalue;
-    } else {
-        newvalue = oldvalue - sensorvalue;
-    }
-    //ALOGI("%s: name: %s sensor: %i old value: %i  new value: %i ", __func__, sensorname, sensorvalue, oldvalue, newvalue);
-    sspWrite(newvalue);
+    if (en)
+        sspValue |= sensorvalue;
+    else
+        sspValue &= ~sensorvalue;
+
+    sspWrite(sspValue);
+
+    pthread_mutex_unlock(&sspEnableLock);
+
     return 0;
 }