ACPI: thermal trip points are read-only

ACPI: thermal trip points are read-only

/proc/acpi/thermal_zone/*/trip_points displays
what the kernel reads from the BIOS via ACPI.

If you echo a string of ':' deliminted numbers to this file
then it will change what it displays.

But it shouldn't, since the kernel has no way to communicate
these changes to ACPI thermal zones.  ACPI thermal zone
trip points are read-only.

The kernel does have the opportunity to ask the BIOS to change
the trip points with _SCP - Set Cooling Policy.

Request Active Cooling Mode:
# echo 0 > /proc/acpi/thermal_zone/*/cooling_policy

Request Passive Cooling Mode:
# echo 1 > /proc/acpi/thermal_zone/*/cooling_policy

However, in practice it is quite rare for the BIOS
to support the optional _SCP, and it is even more rare
for the BIOS to export an _SCP that actually changes
the trip points.

Signed-off-by: Len Brown <len.brown@intel.com>