- Document the latest changes for controlling the fan

- s/Thinklight/ThinkLight/ in two cases

Approved by:	brueffer
MFC after:	1 week

share/man/man4/man4.i386/acpi_ibm.4

@@ -137,7 +137,7 @@ The
 .Nm
 driver provides a
 .Xr led 4
-interface for the Thinklight.
+interface for the ThinkLight.
 The Thinklight can be made to blink by writing
 .Tn ASCII
 strings to the
@@ -269,8 +269,28 @@ Toggle Bluetooth chip activity.
 (read-only)
 Indicates whether the WLAN chip is active or not.
 .It Va dev.acpi_ibm.0.fan
-(read-only)
-Indicates whether the fan is on or off.
+Indicates whether the fan is in automatic (1) or manual (0) mode.
+Default is automatic mode.
+This sysctl should be used with extreme precaution, since disabling automatic
+fan control might overheat the ThinkPad and lead to permanent damage if the
+.Va fan_level
+is not set accordingly.
+.It Va dev.acpi_ibm.0.fan_level
+Indicates at what speed the fan should run when being in manual mode.
+Values are ranging from 0 (off) to 7 (max).
+The resulting speed differs from model to model.
+On a T41p this is as follows:
+.Pp
+.Bl -tag -width indent-two -compact
+.It Li 0
+off
+.It Li 1, 2
+~3000 RPM
+.It Li 3, 4, 5
+~3600 RPM
+.It Li 6, 7
+~4300 RPM
+.El
 .It Va dev.acpi_ibm.0.fan_speed
 (read-only)
 Fan speed in rounds per minute.
@@ -310,7 +330,7 @@ Defaults for these sysctls can be set in
 .Sh FILES
 .Bl -tag -width ".Pa /dev/led/thinklight"
 .It Pa /dev/led/thinklight
-Thinklight
+ThinkLight
 .Xr led 4
 device node
 .El