When the temp goes over the ACPI passive trip point the processor gets
throttled. It usually never goes over T4 before the temp falls below the
passive temp but sometimes it reaches the highest T7. If it reach T7 the
next call to _TMP or _L18 never returns. I've confirmed this by running
echo T7 > /proc/acpi/processor/CPU*/throttling and then tried to read
from /proc/acpi/thermal_zone/TZ00/temperature and it fails in the same way.
I've tried activating the ACPI_LV_PARSE ACPI debug mode, enter T7 and read
from temp. I put the result of that in the trace_debug file at the same adress.
The AML call chain looks like this _TMP -> PMRD -> RCMD -> WIBF
WIBF always returns 1 causing the interpreter to get stuck in the while
loop in PMRD.
While (RCMD (0x80, Local0))
Store (PMUC, Local5)
If (And (Local5, One, Local2))
Store (PMUD, Local5)
This is AML implementation of EC driver... it relies on certain speed
of AML interpreter to work properly (look for Noop inserted as delay).
It is possible to replace this driver with the native Linux one, which
more robust, but this involves heavy DSDT hacking.
Overall, it is heavily mis-designed BIOS, so don't expect it to be fixed
on Linux side.