[PATCH 1/2] HID: input: ignore System Control application usages if not System Controls

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

Microsoft is reusing its report descriptor again and again, and part of it
looks like this:

0x05, 0x01,                    // Usage Page (Generic Desktop)        299
0x09, 0x80,                    // Usage (System Control)              301
0xa1, 0x01,                    // Collection (Application)            303
0x85, 0x03,                    //  Report ID (3)                      305
0x19, 0x00,                    //  Usage Minimum (0)                  307
0x29, 0xff,                    //  Usage Maximum (255)                309
0x15, 0x00,                    //  Logical Minimum (0)                311
0x26, 0xff, 0x00,              //  Logical Maximum (255)              313
0x81, 0x00,                    //  Input (Data,Arr,Abs)               316
0xc0,                          // End Collection                      318

While there is nothing wrong in term of processing, we do however blindly
map the full usage range (it's an array) from 0x00 to 0xff, which creates
some interesting axis, like ABS_X|Y, and a bunch of ABS_MISC + n.

While libinput and other stacks don't care that much (we can detect them),
joydev is very happy and attaches itself to the mouse or keyboard.

The problem is that joydev now handles the device as a joystick, but given
that we have a HID array, it sets all the ABS_* values to 0. And in its
world, 0 means -32767 (minimum value), which sends spurious events to games
(think Steam).

It looks like hid-microsoft tries to tackle the very same problem with its
.report_fixup callback. But fixing the report descriptor is an endless task
and is quite obfuscated.

So take the hammer, and decide that if the application is meant to be
System Control, any other usage not in the System Control range should
be ignored.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1325354
Link: https://bugzilla.kernel.org/show_bug.cgi?id=28912
Link: https://github.com/ValveSoftware/steam-for-linux/issues/3384
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1325354
Link: https://bugzilla.kernel.org/show_bug.cgi?id=37982

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
---
 drivers/hid/hid-input.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 14dd974..55db584 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -604,6 +604,15 @@ static void hidinput_configure_usage(struct hid_input *hidinput, struct hid_fiel
 			break;
 		}
 
+		/*
+		 * Some lazy vendors declare 255 usages for System Control,
+		 * leading to the creation of ABS_X|Y axis and too many others.
+		 * It wouldn't be a problem if joydev doesn't consider the
+		 * device as a joystick then.
+		 */
+		if (field->application == HID_GD_SYSTEM_CONTROL)
+			goto ignore;
+
 		if ((usage->hid & 0xf0) == 0x90) {	/* D-pad */
 			switch (usage->hid) {
 			case HID_GD_UP:	   usage->hat_dir = 1; break;
-- 
2.7.4