hwmon: (w83795) Read the intrusion state properly

We can't read the intrusion state from the real-time alarm registers
as we do for all other alarm flags, because real-time alarm bits don't
stick (by definition) and the intrusion state has to stick until
explicitly cleared (otherwise it has little value.)

So we have to use the interrupt status register instead, which is read
from the same address but with a configuration bit flipped in another
register.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>

drivers/hwmon/w83795.c

@@ -165,10 +165,11 @@ static const u8 IN_LSB_SHIFT_IDX[][2] = {
 
 #define W83795_REG_VID_CTRL		0x6A
 
+#define W83795_REG_ALARM_CTRL		0x40
+#define ALARM_CTRL_RTSACS		(1 << 7)
 #define W83795_REG_ALARM(index)		(0x41 + (index))
-#define W83795_REG_BEEP(index)		(0x50 + (index))
-
 #define W83795_REG_CLR_CHASSIS		0x4D
+#define W83795_REG_BEEP(index)		(0x50 + (index))
 
 
 #define W83795_REG_FCMS1		0x201
@@ -585,6 +586,7 @@ static struct w83795_data *w83795_update_device(struct device *dev)
 	struct i2c_client *client = to_i2c_client(dev);
 	struct w83795_data *data = i2c_get_clientdata(client);
 	u16 tmp;
+	u8 intrusion;
 	int i;
 
 	mutex_lock(&data->update_lock);
@@ -656,9 +658,24 @@ static struct w83795_data *w83795_update_device(struct device *dev)
 		    w83795_read(client, W83795_REG_PWM(i, PWM_OUTPUT));
 	}
 
-	/* update alarm */
+	/* Update intrusion and alarms
+	 * It is important to read intrusion first, because reading from
+	 * register SMI STS6 clears the interrupt status temporarily. */
+	tmp = w83795_read(client, W83795_REG_ALARM_CTRL);
+	/* Switch to interrupt status for intrusion if needed */
+	if (tmp & ALARM_CTRL_RTSACS)
+		w83795_write(client, W83795_REG_ALARM_CTRL,
+			     tmp & ~ALARM_CTRL_RTSACS);
+	intrusion = w83795_read(client, W83795_REG_ALARM(5)) & (1 << 6);
+	/* Switch to real-time alarms */
+	w83795_write(client, W83795_REG_ALARM_CTRL, tmp | ALARM_CTRL_RTSACS);
 	for (i = 0; i < ARRAY_SIZE(data->alarms); i++)
 		data->alarms[i] = w83795_read(client, W83795_REG_ALARM(i));
+	data->alarms[5] |= intrusion;
+	/* Restore original configuration if needed */
+	if (!(tmp & ALARM_CTRL_RTSACS))
+		w83795_write(client, W83795_REG_ALARM_CTRL,
+			     tmp & ~ALARM_CTRL_RTSACS);
 
 	data->last_updated = jiffies;
 	data->valid = 1;