1 files changed, 9 insertions, 1 deletions

diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index f2ff638cce8d..0d5e91379ae8 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -1269,7 +1269,7 @@ Fan control and monitoring: fan speed, fan enable/disable
 
 procfs: /proc/acpi/ibm/fan
 sysfs device attributes: (hwmon "thinkpad") fan1_input, pwm1,
-                          pwm1_enable
+                          pwm1_enable, fan2_input
 sysfs hwmon driver attributes: fan_watchdog
 
 NOTE NOTE NOTE: fan control operations are disabled by default for
@@ -1282,6 +1282,9 @@ from the hardware registers of the embedded controller.  This is known
 to work on later R, T, X and Z series ThinkPads but may show a bogus
 value on other models.
 
+Some Lenovo ThinkPads support a secondary fan.  This fan cannot be
+controlled separately, it shares the main fan control.
+
 Fan levels:
 
 Most ThinkPad fans work in "levels" at the firmware interface.  Level 0
@@ -1412,6 +1415,11 @@ hwmon device attribute fan1_input:
         which can take up to two minutes.  May return rubbish on older
         ThinkPads.
 
+hwmon device attribute fan2_input:
+        Fan tachometer reading, in RPM, for the secondary fan.
+        Available only on some ThinkPads.  If the secondary fan is
+        not installed, will always read 0.
+
 hwmon driver attribute fan_watchdog:
         Fan safety watchdog timer interval, in seconds.  Minimum is
         1 second, maximum is 120 seconds.  0 disables the watchdog.