hwmon: (coretemp) Read TjMax only when refreshing the temperature

show_temp() reads TjMax before checking whether the cached temperature is
still fresh, but consumes it only when recomputing that temperature. On a
cache hit the value is discarded.

Discarding it is not free. On CPUs that report TjMax in
MSR_IA32_TEMPERATURE_TARGET, get_tjmax() returns the value it just read
without storing it in tdata->tjmax, so every call reads the MSR again.
That is a cross-CPU call whenever the CPU owning the sensor is not the
current one, and it is made while holding tdata->update_lock.

Read TjMax where it is used. The value cannot go stale in the meantime:
bits 23:16 of MSR_IA32_TEMPERATURE_TARGET are read-only, and the register
is package-scoped, so every CPU of the package reads the same value.

The temperature reported to userspace does not change.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Link: https://patch.msgid.link/20260924-coretemp-temp-fault-v1-2-1884f0ff97d5@linux.intel.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

0 files changed, 0 insertions, 0 deletions