HID: hid-input: avoid splitting keyboard, system and consumer controls

A typical USB keyboard usually splits its keys into several reports:

- one for the basic alphanumeric keys, modifier keys, F<n> keys, six pack
  keys and keypad. This report's application is normally listed as
  GenericDesktop.Keyboard
- a GenericDesktop.SystemControl report for the system control keys, such
  as power and sleep
- Consumer.ConsumerControl report for multimedia (forward, rewind,
  play/pause, mute, etc) and other extended keys.
- additional output, vendor specific, and feature reports

Splitting each report into a separate input device is wasteful and even
hurts userspace as it makes it harder to determine the true capabilities
(set of available keys) of a keyboard, so let's adjust application
matching to merge system control and consumer control reports with
keyboard report, if one has already been processed.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-input.c

@@ -1852,6 +1852,16 @@ static struct hid_input *hidinput_match_application(struct hid_report *report)
 	list_for_each_entry(hidinput, &hid->inputs, list) {
 		if (hidinput->application == report->application)
 			return hidinput;
+
+		/*
+		 * Keep SystemControl and ConsumerControl applications together
+		 * with the main keyboard, if present.
+		 */
+		if ((report->application == HID_GD_SYSTEM_CONTROL ||
+		     report->application == HID_CP_CONSUMER_CONTROL) &&
+		    hidinput->application == HID_GD_KEYBOARD) {
+			return hidinput;
+		}
 	}
 
 	return NULL;