sim/thermal: Exercise the devfreq cooling path.

The dummy driver's frequency cooling device is now a devfreq one, so the
configuration that tests it needs devfreq built.  This is a change in what
the configuration covers, not just a symbol rename: nothing in the tree
registered a devfreq device before, and this is now the one place the
thermal to devfreq path runs without hardware.

Walking the dummy zone from 45 to 90 degrees steps the device through
every entry of its table, 900 down to 100, and back up as it cools.

The documentation follows the same rename, and devfreq's own page now says
that thermal is a requester and that a driver expecting to be throttled
wants DEVFREQ_CONFLICT_PREFER_LOW.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>

Documentation/components/drivers/special/devfreq.rst

@@ -52,6 +52,20 @@ aggregate ``max``) the driver's ``conflict_policy`` decides who wins:
 - ``DEVFREQ_CONFLICT_PREFER_LOW`` clamps to the ceiling and chooses the lower
   frequency. A device protecting a thermal or power budget picks this.
 
+The thermal framework is one such requester. With
+``CONFIG_THERMAL_CDEV_DEVFREQ`` it registers a cooling device over the
+devfreq device named by ``CONFIG_THERMAL_CDEV_DEVFREQ_NAME``, and each
+cooling state installs a ceiling one entry further down the table. Drivers
+that expect to be throttled should carry ``DEVFREQ_CONFLICT_PREFER_LOW``, so
+that the ceiling wins against anything asking for more.
+
+A table of *n* usable frequencies gives the cooling device a maximum state of
+*n* - 1: state zero caps at the highest frequency, which leaves the device
+unthrottled, and the maximum state caps at the lowest. Entries of
+``DEVFREQ_ENTRY_INVALID`` are not frequencies the device can be held at, so
+they earn no state, and the ``low`` and ``high`` bounds of a thermal zone's
+cooling map therefore count usable frequencies rather than table positions.
+
 The resolved ``[min, max]`` is then snapped to the table: ``min`` rounds up to
 the lowest entry at or above it, ``max`` rounds down to the highest entry at
 or below it. The governor picks within that snapped range, and the lower half

Documentation/components/drivers/thermal/index.rst

@@ -8,7 +8,7 @@ Brief
 =====
 1. Support Zone, Cooling Device and Governor
     - ``Zone``: Responsible for monitoring the temperature of the specified area, obtains the temperature through the temperature sensor, and the sensor driver returns the temperature through callback function.
-    - ``Cooling Device``: A cooling device is a device that can reduce the temperature by using resources such as cpufreq, fan, etc. The cpufreq cooling device driver is preset to simplify CPU frequency modulation temperature control.
+    - ``Cooling Device``: A cooling device is a device that can reduce the temperature by using resources such as devfreq, fan, etc. The devfreq cooling device driver is preset to simplify frequency modulation temperature control: it caps the frequency of the devfreq device named by ``CONFIG_THERMAL_CDEV_DEVFREQ_NAME``, which must be registered before ``thermal_init()`` runs.
     - ``Governor``: For temperature control, you can use the preset or custom registered one, preset "step_wise" governor:
         - When the temperature of the "Zone" reaches the temperature trip point, and the temperature change trend rises or stabilizes ("step_wise" obtains the value of the corresponding "Zone" every 20ms [``CONFIG_THERMAL_DUMMY_POLLING_DELAY=200``, ``CONFIG_USEC_PER_TICK=100``]), the current temperature equals to OR greater than the last obtained temperature value), improve the state of the "Cooling Device" (trigger the cooling operation executed by the corresponding state, Through ``set_state``).
         - When the temperature of the zone is lower than the temperature trip point, and the temperature trend is steadily decreasing, the state of the "Cooling Device" is reduced.
@@ -80,8 +80,8 @@ Device Driver
 
         nsh> cat /proc/thermal/cpu-thermal
         z:cpu-thermal t:77 t:1 h:16 l:0 c:fan0 s:7|7
-        z:cpu-thermal t:77 t:1 h:3 l:3 c:cpufreq s:3|3
-        z:cpu-thermal t:77 t:2 h:2 l:0 c:cpufreq s:3|2
+        z:cpu-thermal t:77 t:1 h:3 l:3 c:cpu s:3|3
+        z:cpu-thermal t:77 t:2 h:2 l:0 c:cpu s:3|2
 
 Board Customization
 ===================
@@ -127,7 +127,7 @@ The binding relationship between Trip, Cooling Device, Governor and Zone is show
   {
     {
       .trip_name = "cpu_alert1",
-      .cdev_name = "cpufreq",
+      .cdev_name = CONFIG_THERMAL_CDEV_DEVFREQ_NAME,
       .low    = 3,
       .high   = THERMAL_NO_LIMIT,
       .weight = 20
@@ -141,7 +141,7 @@ The binding relationship between Trip, Cooling Device, Governor and Zone is show
     },
     {
       .trip_name = "cpu_alert0",
-      .cdev_name = "cpufreq",
+      .cdev_name = CONFIG_THERMAL_CDEV_DEVFREQ_NAME,
       .low    = THERMAL_NO_LIMIT,
       .high   = 2,
       .weight = 20

boards/sim/sim/sim/configs/thermal/defconfig

@@ -4,9 +4,12 @@ CONFIG_DEBUG_THERMAL=y
 CONFIG_DEBUG_THERMAL_ERROR=y
 CONFIG_DEBUG_THERMAL_INFO=y
 CONFIG_DEBUG_THERMAL_WARN=y
+CONFIG_DEVFREQ=y
+CONFIG_DEVFREQ_PROCFS=y
 CONFIG_PM=y
 CONFIG_READLINE_CMD_HISTORY=y
 CONFIG_SCHED_LPWORK=y
 CONFIG_THERMAL=y
 CONFIG_THERMAL_DUMMY=y
+CONFIG_THERMAL_DUMMY_DEVFREQ=y
 CONFIG_THERMAL_PROCFS=y