Does ACPI thermal driver support temperature under zero?

Hi,

My colleague was testing the system booting in temprature at -20 ℃, then the system print "thermal_sys: Critical temperature reached (244 C), shutting down", and the system shutdown as not expected.

The system is using avoton CPU and the kernel version is 3.4 stable, I just find that in the latest of version of kernel, all the temperature variable in thermal structure is unsigned, it seems that in thermal_get_temp() in drivers/acpi/thermal.c, *temp will be a large value if temperature under zero, did I miss something?

Any help or guidance will be appreciated a lot.

Thanks
Hanjun