From cccfc9c4bb3c7888f8249b36e08d6e115238c613 Mon Sep 17 00:00:00 2001
From: Jean Delvare <khali@linux-fr.org>
Date: Fri, 5 Mar 2010 22:17:21 +0100
Subject: [PATCH] hwmon: (it87) Validate auto pwm settings

Before switching to automatic fan control mode, make sure that all the
trip points make sense. Otherwise, the control loop could lead to
weird fan behavior.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
---
 Documentation/hwmon/it87 |  4 ++++
 drivers/hwmon/it87.c     | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/Documentation/hwmon/it87 b/Documentation/hwmon/it87
index 0083bd317351..8d08bf0d38ed 100644
--- a/Documentation/hwmon/it87
+++ b/Documentation/hwmon/it87
@@ -177,3 +177,7 @@ between trip point N and trip point N+1 then the PWM output value is
 the one of trip point N. The automatic control mode is less flexible
 than the manual control mode, but it reacts faster, is more robust and
 doesn't use CPU cycles.
+
+Trip points must be set properly before switching to automatic fan speed
+control mode. The driver will perform basic integrity checks before
+actually switching to automatic control mode.
diff --git a/drivers/hwmon/it87.c b/drivers/hwmon/it87.c
index bbb0c7443b9b..1002befd87d5 100644
--- a/drivers/hwmon/it87.c
+++ b/drivers/hwmon/it87.c
@@ -719,6 +719,32 @@ static ssize_t set_fan_div(struct device *dev, struct device_attribute *attr,
 	mutex_unlock(&data->update_lock);
 	return count;
 }
+
+/* Returns 0 if OK, -EINVAL otherwise */
+static int check_trip_points(struct device *dev, int nr)
+{
+	const struct it87_data *data = dev_get_drvdata(dev);
+	int i, err = 0;
+
+	if (has_old_autopwm(data)) {
+		for (i = 0; i < 3; i++) {
+			if (data->auto_temp[nr][i] > data->auto_temp[nr][i + 1])
+				err = -EINVAL;
+		}
+		for (i = 0; i < 2; i++) {
+			if (data->auto_pwm[nr][i] > data->auto_pwm[nr][i + 1])
+				err = -EINVAL;
+		}
+	}
+
+	if (err) {
+		dev_err(dev, "Inconsistent trip points, not switching to "
+			"automatic mode\n");
+		dev_err(dev, "Adjust the trip points and try again\n");
+	}
+	return err;
+}
+
 static ssize_t set_pwm_enable(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t count)
 {
@@ -731,6 +757,12 @@ static ssize_t set_pwm_enable(struct device *dev,
 	if (strict_strtol(buf, 10, &val) < 0 || val < 0 || val > 2)
 		return -EINVAL;
 
+	/* Check trip points before switching to automatic mode */
+	if (val == 2) {
+		if (check_trip_points(dev, nr) < 0)
+			return -EINVAL;
+	}
+
 	mutex_lock(&data->update_lock);
 
 	if (val == 0) {