Doc/PM: Sync with intel_powerclamp code behavior

Commit feb6cd6a0f9f ("thermal/intel_powerclamp: stop sched tick in forced
idle") changed how idle injection accouting, so we need to update
the documentation accordingly.

This patch also expands more details on the behavior of cur_state.

Signed-off-by: Jacob Pan <[e-mail]>
Reported-by: Wang, Xiaolong <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/thermal/intel_powerclamp.txt

···
 max_state:50
 type:intel_powerclamp
 
+cur_state allows user to set the desired idle percentage. Writing 0 to
+cur_state will stop idle injection. Writing a value between 1 and
+max_state will start the idle injection. Reading cur_state returns the
+actual and current idle percentage. This may not be the same value
+set by the user in that current idle percentage depends on workload
+and includes natural idle. When idle injection is disabled, reading
+cur_state returns value -1 instead of 0 which is to avoid confusing
+100% busy state with the disabled state.
+
 Example usage:
 - To inject 25% idle time
 $ sudo sh -c "echo 25 > /sys/class/thermal/cooling_device80/cur_state
···
 will not show idle injection kernel threads.
 
 If the system is busy (spin test below) and has less than 25% natural
-idle time, powerclamp kernel threads will do idle injection, which
-appear running to the scheduler. But the overall system idle is still
-reflected. In this example, 24.1% idle is shown. This helps the
-system admin or user determine the cause of slowdown, when a
-powerclamp driver is in action.
+idle time, powerclamp kernel threads will do idle injection. Forced
+idle time is accounted as normal idle in that common code path is
+taken as the idle task.
+
+In this example, 24.1% idle is shown. This helps the system admin or
+user determine the cause of slowdown, when a powerclamp driver is in action.
 
 
 Tasks: 197 total,   1 running, 196 sleeping,   0 stopped,   0 zombie