1 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/ibm-acpi.txt b/Documentation/ibm-acpi.txt
index cbd3a603a7ef..0132d363feb5 100644
--- a/Documentation/ibm-acpi.txt
+++ b/Documentation/ibm-acpi.txt
@@ -670,6 +670,26 @@ example:
 
         modprobe ibm_acpi hotkey=enable,0xffff video=auto_disable
 
+The ibm-acpi kernel driver can be programmed to revert the fan level
+to a safe setting if userspace does not issue one of the fan commands:
+"enable", "disable", "level" or "watchdog" within a configurable
+ammount of time.  To do this, use the "watchdog" command.
+
+        echo 'watchdog <interval>' > /proc/acpi/ibm/fan
+
+Interval is the ammount of time in seconds to wait for one of the
+above mentioned fan commands before reseting the fan level to a safe
+one.  If set to zero, the watchdog is disabled (default).  When the
+watchdog timer runs out, it does the exact equivalent of the "enable"
+fan command.
+
+Note that the watchdog timer stops after it enables the fan.  It will
+be rearmed again automatically (using the same interval) when one of
+the above mentioned fan commands is received.  The fan watchdog is,
+therefore, not suitable to protect against fan mode changes made
+through means other than the "enable", "disable", and "level" fan
+commands.
+
 
 Example Configuration
 ---------------------