ACPI: thinkpad-acpi: add sysfs support to the thermal subdriver

Export thinkpad thermal sensors to sysfs, following the hwmon
specification for thermal monitoring sensors.

ThinkPad thermal monitoring is done by the EC.  Sensors can show up or
disappear at runtime when they are inside hotswappable hardware, such as
batteries.  Sensors that are not available return -ENXIO when accessed.

Up to 16 thermal sensors are supported on new firmware (but nobody has
reported a ThinkPad with more than 12 sensors so far), and 8 sensors are
supported on older firmware.  Thermal sensor mapping is model-specific.
Precision varies, it is 1 degree Celcius on new ThinkPads, but higher on
some older models.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 20 insertions, 6 deletions

diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt
index cc079afaf66b..80c0bf28e392 100644
--- a/Documentation/thinkpad-acpi.txt
+++ b/Documentation/thinkpad-acpi.txt
@@ -458,17 +458,17 @@ X40:
         16 - one medium-pitched beep repeating constantly, stop with 17
         17 - stop 16
 
-Temperature sensors -- /proc/acpi/ibm/thermal
----------------------------------------------
+Temperature sensors
+-------------------
+
+procfs: /proc/acpi/ibm/thermal
+sysfs device attributes: (hwmon) temp*_input
 
 Most ThinkPads include six or more separate temperature sensors but
 only expose the CPU temperature through the standard ACPI methods.
 This feature shows readings from up to eight different sensors on older
 ThinkPads, and it has experimental support for up to sixteen different
-sensors on newer ThinkPads.  Readings from sensors that are not available
-return -128.
-
-No commands can be written to this file.
+sensors on newer ThinkPads.
 
 EXPERIMENTAL: The 16-sensors feature is marked EXPERIMENTAL because the
 implementation directly accesses hardware registers and may not work as
@@ -525,6 +525,20 @@ The A31 has a very atypical layout for the thermal sensors
 8:  Bay Battery: secondary sensor
 
 
+Procfs notes:
+        Readings from sensors that are not available return -128.
+        No commands can be written to this file.
+
+Sysfs notes:
+        Sensors that are not available return the ENXIO error.  This
+        status may change at runtime, as there are hotplug thermal
+        sensors, like those inside the batteries and docks.
+
+        thinkpad-acpi thermal sensors are reported through the hwmon
+        subsystem, and follow all of the hwmon guidelines at
+        Documentation/hwmon.
+
+
 EXPERIMENTAL: Embedded controller register dump -- /proc/acpi/ibm/ecdump
 ------------------------------------------------------------------------