Only map x and y to axes 0 and 1

The Logitech G600 has one device with all axes north of ABS_MISC. The current
code assigns ABS_MISC as first axis to map to axis 0, i.e. x. On button press,
one node sends the BTN_LEFT but the other node sends an ABS_MISC with a 1 0
value. ABS_MISC is mapped to axis 0, this moves the pointer to (0, y) on
every button click.

Avoid this by simply mapping any axis other than x/y to at least axis 3, and
make sure we only override the MT 0/1 axes when we actually have MT axes.

https://bugs.freedesktop.org/show_bug.cgi?id=92856

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>

src/evdev.c

@@ -1377,7 +1377,7 @@ EvdevAddAbsValuatorClass(DeviceIntPtr device, int num_scroll_axes)
     }
     atoms = malloc((pEvdev->num_vals + num_mt_axes) * sizeof(Atom));
 
-    i = 0;
+    i = 2;
     for (axis = ABS_X; i < MAX_VALUATORS && axis <= ABS_MAX; axis++) {
         int j;
         pEvdev->abs_axis_map[axis] = -1;
@@ -1385,9 +1385,14 @@ EvdevAddAbsValuatorClass(DeviceIntPtr device, int num_scroll_axes)
             is_blacklisted_axis(axis))
             continue;
 
-        mapping = i;
+        if (axis == ABS_X)
+            mapping = 0;
+        else if (axis == ABS_Y)
+            mapping = 1;
+        else
+            mapping = i;
 
-        for (j = 0; j < ArrayLength(mt_axis_mappings); j++)
+        for (j = 0; !pEvdev->fake_mt && j < ArrayLength(mt_axis_mappings); j++)
         {
             if (mt_axis_mappings[j].code == axis)
                 mt_axis_mappings[j].mapping = mapping;