i8k: Fix temperature bug handling in i8k_get_temp()

Static array prev[] was incorrectly initialized. It should be initialized to
some "invalid" temperature value (above I8K_MAX_TEMP).

Next, function should store "invalid" value to prev[] (above I8K_MAX_TEMP),
not valid (= I8K_MAX_TEMP) because whole temperature bug handling will not
work.

And last part, to not break existing detection of temperature sensors, register
them also if i8k report too high temperature (above I8K_MAX_TEMP). This is
needed because some sensors are sometimes turned off (e.g sensor on GPU which
can be turned off/on) and in this case SMM report too high value.

To prevent reporting "invalid" values to userspace, return -EINVAL. In this case
sensors which are currently turned off (e.g optimus/powerexpress/enduro gpu)
are reported as "N/A" by lm-sensors package.
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/i8k.c

@@ -298,7 +298,7 @@ static int i8k_get_temp(int sensor)
 	int temp;
 
 #ifdef I8K_TEMPERATURE_BUG
-	static int prev[4];
+	static int prev[4] = { I8K_MAX_TEMP+1, I8K_MAX_TEMP+1, I8K_MAX_TEMP+1, I8K_MAX_TEMP+1 };
 #endif
 	regs.ebx = sensor & 0xff;
 	rc = i8k_smm(&regs);
@@ -317,10 +317,12 @@ static int i8k_get_temp(int sensor)
 	 */
 	if (temp > I8K_MAX_TEMP) {
 		temp = prev[sensor];
-		prev[sensor] = I8K_MAX_TEMP;
+		prev[sensor] = I8K_MAX_TEMP+1;
 	} else {
 		prev[sensor] = temp;
 	}
+	if (temp > I8K_MAX_TEMP)
+		return -ERANGE;
 #endif
 
 	return temp;
@@ -499,6 +501,8 @@ static ssize_t i8k_hwmon_show_temp(struct device *dev,
 	int temp;
 
 	temp = i8k_get_temp(index);
+	if (temp == -ERANGE)
+		return -EINVAL;
 	if (temp < 0)
 		return temp;
 	return sprintf(buf, "%d\n", temp * 1000);
@@ -610,17 +614,17 @@ static int __init i8k_init_hwmon(void)
 
 	/* CPU temperature attributes, if temperature reading is OK */
 	err = i8k_get_temp(0);
-	if (err >= 0)
+	if (err >= 0 || err == -ERANGE)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP1;
 	/* check for additional temperature sensors */
 	err = i8k_get_temp(1);
-	if (err >= 0)
+	if (err >= 0 || err == -ERANGE)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP2;
 	err = i8k_get_temp(2);
-	if (err >= 0)
+	if (err >= 0 || err == -ERANGE)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP3;
 	err = i8k_get_temp(3);
-	if (err >= 0)
+	if (err >= 0 || err == -ERANGE)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP4;
 
 	/* Left fan attributes, if left fan is present */