hwmon: (amc6821) Make reading and writing fan speed limits consistent

The default value of the maximum fan speed limit register is 0,
essentially translating to an unlimited fan speed. When reading
the limit, a value of 0 is reported in this case. However, writing
a value of 0 results in writing a value of 0xffff into the register,
which is inconsistent.

To solve the problem, permit writing a limit of 0 for the maximim fan
speed, effectively translating to "no limit". Write 0 into the register
if a limit value of 0 is written. Otherwise limit the range to
<1..6000000> and write 1..0xffff into the register. This ensures that
reading and writing from and to a limit register return the same value
while at the same time not changing reported values when reading the
speed or limits.

While at it, restrict fan limit writes to non-negative numbers; writing
a negative limit does not make sense and should be reported instead of
being corrected.

Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c
index dc35e9b21f912c344a73cdcad3f8447c764958ff..8e3cc33d8073c6b66f410e9b4d2e0bbbaffc8e97 100644 (file)
--- a/drivers/hwmon/amc6821.c
+++ b/drivers/hwmon/amc6821.c
@@ -616,15 +616,20 @@ static ssize_t fan_store(struct device *dev, struct device_attribute *attr,
 {
        struct amc6821_data *data = dev_get_drvdata(dev);
        struct i2c_client *client = data->client;
-       long val;
+       unsigned long val;
        int ix = to_sensor_dev_attr(attr)->index;
-       int ret = kstrtol(buf, 10, &val);
+       int ret = kstrtoul(buf, 10, &val);
        if (ret)
                return ret;
-       val = 1 > val ? 0xFFFF : 6000000/val;
+
+       /* The minimum fan speed must not be unlimited (0) */
+       if (ix == IDX_FAN1_MIN && !val)
+               return -EINVAL;
+
+       val = val > 0 ? 6000000 / clamp_val(val, 1, 6000000) : 0;
 
        mutex_lock(&data->update_lock);
-       data->fan[ix] = (u16) clamp_val(val, 1, 0xFFFF);
+       data->fan[ix] = clamp_val(val, 0, 0xFFFF);
        if (i2c_smbus_write_byte_data(client, fan_reg_low[ix],
                        data->fan[ix] & 0xFF)) {
                dev_err(&client->dev, "Register write error, aborting.\n");