hwmon: Introduce 64-bit energy attribute support

Many chips require 64-bit variables to display the accumulated energy,
even more so since the energy units are micro-Joule. Add new sensor type
"energy64" to support reporting the chip energy as 64-bit values.

Changing the entire hardware monitoring API is not feasible, and it is only
really necessary to support reading 64-bit values for the "energyX_input"
attribute. For this reason, keep the API as-is and use type casts on both
ends to pass 64-bit pointers when reading the accumulated energy. On the
write side (which is only useful for the energyX_enable attribute), keep
passing the written value as long.

Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz> # INA780
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/hwmon-kernel-api.rst

@@ -159,6 +159,7 @@ It contains following fields:
      hwmon_curr		Current sensor
      hwmon_power		Power sensor
      hwmon_energy	Energy sensor
+     hwmon_energy64	Energy sensor, reported as 64-bit signed value
      hwmon_humidity	Humidity sensor
      hwmon_fan		Fan speed sensor
      hwmon_pwm		PWM control
@@ -288,6 +289,8 @@ Parameters:
 		The sensor channel number.
 	val:
 		Pointer to attribute value.
+		For hwmon_energy64, `'val`' is passed as `long *` but needs
+		a typecast to `s64 *`.
 
 Return value:
 	0 on success, a negative error number otherwise.