Detect non-standard joystick buttons

The Xbox One S controller when connected via Bluetooth
is exposing its select button with the Linux KEY_BACK
code, which is outside of the normal input code
scan range for joysticks.  This patch adds additional
scanning to pick up such extra buttons, and adds
them as buttons after the normal ranges to preserve
compatibility with existing key mappings.

input/drivers_joypad/udev_joypad.c

@@ -118,7 +118,7 @@ static void udev_poll_pad(struct udev_joypad *pad, unsigned p)
          switch (events[i].type)
          {
             case EV_KEY:
-               if (code >= BTN_MISC || (code >= KEY_UP && code <= KEY_DOWN))
+               if (code >= 0 && code < KEY_MAX)
                {
                   if (events[i].value)
                      BIT64_SET(pad->buttons, pad->button_bind[code]);
@@ -253,6 +253,15 @@ static int udev_add_pad(struct udev_device *dev, unsigned p, int fd, const char
    for (i = BTN_MISC; i < KEY_MAX && buttons < UDEV_NUM_BUTTONS; i++)
       if (test_bit(i, keybit))
          pad->button_bind[i] = buttons++;
+   /* The following two ranges are scanned and added after the above
+    * ranges to maintain compatibility with existing key maps.
+    */
+   for (i = 0; i < KEY_UP && buttons < UDEV_NUM_BUTTONS; i++)
+      if (test_bit(i, keybit))
+         pad->button_bind[i] = buttons++;
+   for (i = KEY_DOWN + 1; i < BTN_MISC && buttons < UDEV_NUM_BUTTONS; i++)
+      if (test_bit(i, keybit))
+         pad->button_bind[i] = buttons++;
    for (i = 0; i < ABS_MISC && axes < NUM_AXES; i++)
    {
       /* Skip hats for now. */