[PATCH v2] hwmon: (nct7802) Fix overflows seen when writing into limit attributes

[Guenter Roeck <linux@roeck-us.net>]

Fix overflows seen when writing voltage and temperature limit attributes.

The value passed to DIV_ROUND_CLOSEST() needs to be clamped, and the
value parameter passed to nct7802_write_fan_min() is an unsigned long.

Also, writing values larger than 2700000 into a limit attribute results
in writing 0 into the chip's limit registers. The exact behavior when
writing this value is unspecified. For consistency, report a limit of
1350000 if the chip register reads 0.  This may be wrong, and the chip
behavior should be verified with the actual chip, but it is better than
reporting a value of 0 (which, if written, results in writing a value
of 0x1fff into the chip register).

Fixes: 3434f3783580 ("hwmon: Driver for Nuvoton NCT7802Y")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v2: When reading a register value of 0 from a limit register,
    report it as speed of 1350000.
    Avoid overflow due to different variable types passed to
    nct7802_write_fan_min().
    Fix low limit in store_temp (-128, not -127 as in v1).

 drivers/hwmon/nct7802.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/nct7802.c b/drivers/hwmon/nct7802.c
index 3ce33d244cc0..12b94b094c0d 100644
--- a/drivers/hwmon/nct7802.c
+++ b/drivers/hwmon/nct7802.c
@@ -259,13 +259,15 @@ static int nct7802_read_fan_min(struct nct7802_data *data, u8 reg_fan_low,
 		ret = 0;
 	else if (ret)
 		ret = DIV_ROUND_CLOSEST(1350000U, ret);
+	else
+		ret = 1350000U;
 abort:
 	mutex_unlock(&data->access_lock);
 	return ret;
 }
 
 static int nct7802_write_fan_min(struct nct7802_data *data, u8 reg_fan_low,
-				 u8 reg_fan_high, unsigned int limit)
+				 u8 reg_fan_high, unsigned long limit)
 {
 	int err;
 
@@ -326,8 +328,8 @@ static int nct7802_write_voltage(struct nct7802_data *data, int nr, int index,
 	int shift = 8 - REG_VOLTAGE_LIMIT_MSB_SHIFT[index - 1][nr];
 	int err;
 
+	voltage = clamp_val(voltage, 0, 0x3ff * nct7802_vmul[nr]);
 	voltage = DIV_ROUND_CLOSEST(voltage, nct7802_vmul[nr]);
-	voltage = clamp_val(voltage, 0, 0x3ff);
 
 	mutex_lock(&data->access_lock);
 	err = regmap_write(data->regmap,
@@ -402,7 +404,7 @@ static ssize_t store_temp(struct device *dev, struct device_attribute *attr,
 	if (err < 0)
 		return err;
 
-	val = clamp_val(DIV_ROUND_CLOSEST(val, 1000), -128, 127);
+	val = DIV_ROUND_CLOSEST(clamp_val(val, -128000, 127000), 1000);
 
 	err = regmap_write(data->regmap, nr, val & 0xff);
 	return err ? : count;
-- 
2.5.0