[smartmontools-support] [PATCH] RFC: libata: Add hwmon support for SMART temperature sensors

[Guenter Roeck]

On 08/09/2018 09:15 PM, Guenter Roeck wrote:
> On 08/09/2018 03:24 PM, Linus Walleij wrote:
>> S.M.A.R.T. temperature sensors have been supported for
>> years by userspace tools such as smarttools.
>>
>> The temperature readout is however also a good fit for
>> Linux' hwmon subsystem. By adding a hwmon interface to dig
>> out SMART parameter 194, we can expose the drive temperature
>> as a standard hwmon sensor.
>>
[ ... ]
>> +
>> +static int ata_hwmon_read_temp(struct ata_hwmon *ata, int *temp,
>> +                   int *min, int *max)
>> +{

[ ... ]

>> +        if (id == SMART_TEMP_PROP_194)
>> +            break;

231 also seems to report the temperature if available, as does 190.

Not sure if 190 is worth it, though - Samsung SSD 840 PRO Series supports
it but reports a static value of 28. And it seems to be either as
degrees C or as 100 - degrees C, depending on the drive manufacturer,
which makes it quite unreliable.

[ ... ]

>> +
>> +static int ata_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>> +              u32 attr, int channel, long *val)
>> +{
>> +    struct ata_hwmon *ata = dev_get_drvdata(dev);
>> +    int temp, min, max;
>> +    int ret;
>> +
>> +    if (type != hwmon_temp)
>> +        return -EINVAL;
>> +
>> +    ret = ata_hwmon_read_temp(ata, &temp, &min, &max);
>> +    if (ret)
>> +        return ret;
>> +
>> +    switch (attr) {
>> +    case hwmon_temp_input:
>> +        *val = temp;
>> +        break;
>> +    case hwmon_temp_min:
>> +        *val = min;
>> +        break;
>> +    case hwmon_temp_max:
>> +        *val = max;
>> +        break;

Those numbers need to be multiplied by 1,000 (hwmon ABI expects milli-degrees C).

Guenter