HID: hid-lg4ff: Allow switching of Logitech gaming wheels between compatibility modes

Allow switching of Logitech gaming wheels between available compatibility modes
through sysfs. This only applies to multimode wheels.

Signed-off-by: Michal Malý <madcatxster@devoid-pointer.net>
Tested-by: Simon Wood <simon@mungewell.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 26 insertions, 1 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-hid-logitech-lg4ff b/Documentation/ABI/testing/sysfs-driver-hid-logitech-lg4ff
index 60f24a1d8119..b3f6a2ac5007 100644
--- a/Documentation/ABI/testing/sysfs-driver-hid-logitech-lg4ff
+++ b/Documentation/ABI/testing/sysfs-driver-hid-logitech-lg4ff
@@ -15,7 +15,32 @@ Description:	Displays a set of alternate modes supported by a wheel. Each
                   Tag: Mode Name
                 Currently active mode is marked with an asterisk. List also
                 contains an abstract item "native" which always denotes the
-                native mode of the wheel.
+                native mode of the wheel. Echoing the mode tag switches the
+                wheel into the corresponding mode. Depending on the exact model
+                of the wheel not all listed modes might always be selectable.
+                If a wheel cannot be switched into the desired mode, -EINVAL
+                is returned accompanied with an explanatory message in the
+                kernel log.
+                This entry is not created for devices that have only one mode.
+
+                Currently supported mode switches:
+                Driving Force Pro:
+                  DF-EX --> DFP
+
+                G25:
+                  DF-EX --> DFP --> G25
+
+                G27:
+                  DF-EX <*> DFP <-> G25 <-> G27
+                  DF-EX <*--------> G25 <-> G27
+                  DF-EX <*----------------> G27
+
+                DFGT:
+                  DF-EX <*> DFP <-> DFGT
+                  DF-EX <*--------> DFGT
+
+                * hid_logitech module must be loaded with lg4ff_no_autoswitch=1
+                  parameter set in order for the switch to DF-EX mode to work.
 
 What:           /sys/bus/hid/drivers/logitech/<dev>/real_id
 Date:           Feb 2015