thermal/drivers/int340x: Do not set a wrong tcc offset on resume

After upgrading to Linux 5.13.3 I noticed my laptop would shutdown due
to overheat (when it should not). It turned out this was due to commit
fe6a6de669 ("thermal/drivers/int340x/processor_thermal: Fix tcc setting").

What happens is this drivers uses a global variable to keep track of the
tcc offset (tcc_offset_save) and uses it on resume. The issue is this
variable is initialized to 0, but is only set in
tcc_offset_degree_celsius_store, i.e. when the tcc offset is explicitly
set by userspace. If that does not happen, the resume path will set the
offset to 0 (in my case the h/w default being 3, the offset would become
too low after a suspend/resume cycle).

The issue did not arise before commit fe6a6de669, as the function
setting the offset would return if the offset was 0. This is no longer
the case (rightfully).

Fix this by not applying the offset if it wasn't saved before, reverting
back to the old logic. A better approach will come later, but this will
be easier to apply to stable kernels.

The logic to restore the offset after a resume was there long before
commit fe6a6de669, but as a value of 0 was considered invalid I'm
referencing the commit that made the issue possible in the Fixes tag
instead.

Fixes: fe6a6de669 ("thermal/drivers/int340x/processor_thermal: Fix tcc setting")
Cc: stable@vger.kernel.org
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Tested-by: Srinivas Pandruvada <srinivas.pI andruvada@linux.intel.com>
Link: https://lore.kernel.org/r/20210909085613.5577-2-atenart@kernel.org

drivers/thermal/intel/int340x_thermal/processor_thermal_device.c

@@ -107,7 +107,7 @@ static int tcc_offset_update(unsigned int tcc)
 	return 0;
 }
 
-static unsigned int tcc_offset_save;
+static int tcc_offset_save = -1;
 
 static ssize_t tcc_offset_degree_celsius_store(struct device *dev,
 				struct device_attribute *attr, const char *buf,
@@ -352,6 +352,7 @@ int proc_thermal_resume(struct device *dev)
 	proc_dev = dev_get_drvdata(dev);
 	proc_thermal_read_ppcc(proc_dev);
 
+	if (tcc_offset_save >= 0)
 		tcc_offset_update(tcc_offset_save);
 
 	return 0;