[PATCH] I2C: Another it87 patch.

This is against my last.

While the old code most definitely did /something/ to the register for
setting the fan div, the 'what' is a more interesting question.

To be honest I could not figure out what it was trying to do, because
the way it was inserting values disagreed with not only the data sheet,
but how it parsed the very same register.

This corrects the issue, and allows one to properly control the divisor
on all 3 fans, including the (much more limited) 3rd fan.

drivers/i2c/chips/it87.c

@@ -159,7 +159,14 @@ static inline u8 FAN_TO_REG(long rpm, int div)
 				205-(val)*5)
 #define ALARMS_FROM_REG(val) (val)
 
-#define DIV_TO_REG(val) ((val)==8?3:(val)==4?2:(val)==1?0:1)
+static int log2(int val)
+{
+	int answer = 0;
+	while ((val >>= 1))
+		answer++;
+	return answer;
+}
+#define DIV_TO_REG(val) log2(val)
 #define DIV_FROM_REG(val) (1 << (val))
 
 /* Initial limits. Use the config file to set better limits. */
@@ -520,10 +527,25 @@ static ssize_t set_fan_div(struct device *dev, const char *buf,
 	struct i2c_client *client = to_i2c_client(dev);
 	struct it87_data *data = i2c_get_clientdata(client);
 	int val = simple_strtol(buf, NULL, 10);
-	int old = it87_read_value(client, IT87_REG_FAN_DIV);
-	data->fan_div[nr] = DIV_TO_REG(val);
-	old = (old & 0x0f) | (data->fan_div[1] << 6) | (data->fan_div[0] << 4);
-	it87_write_value(client, IT87_REG_FAN_DIV, old);
+	u8 old = it87_read_value(client, IT87_REG_FAN_DIV);
+
+	switch (nr) {
+	case 0:
+	case 1:
+		data->fan_div[nr] = DIV_TO_REG(val);
+		break;
+	case 2:
+		if (val < 8)
+			data->fan_div[nr] = 1;
+		else
+			data->fan_div[nr] = 3;
+	}
+	val = old & 0x100;
+	val |= (data->fan_div[0] & 0x07);
+	val |= (data->fan_div[1] & 0x07) << 3;
+	if (data->fan_div[2] == 3)
+		val |= 0x1 << 6;
+	it87_write_value(client, IT87_REG_FAN_DIV, val);
 	return count;
 }
 
@@ -961,7 +983,7 @@ static void it87_update_client(struct i2c_client *client)
 		i = it87_read_value(client, IT87_REG_FAN_DIV);
 		data->fan_div[0] = i & 0x07;
 		data->fan_div[1] = (i >> 3) & 0x07;
-		data->fan_div[2] = 1;
+		data->fan_div[2] = (i & 0x40) ? 3 : 1;
 
 		data->alarms =
 			it87_read_value(client, IT87_REG_ALARM1) |