HID: core: fix grouping by application

commit f07b3c1da92d ("HID: generic: create one input report per
application type") was effectively the same as MULTI_INPUT:
hidinput->report was never set, so hidinput_match_application()
always returned null.

Fix that by testing against the real application.

Note that this breaks some old eGalax touchscreens that expect MULTI_INPUT
instead of HID_QUIRK_INPUT_PER_APP. Enable this quirk for backward
compatibility on all non-Win8 touchscreens.

link: https://bugzilla.kernel.org/show_bug.cgi?id=200847
link: https://bugzilla.kernel.org/show_bug.cgi?id=200849
link: https://bugs.archlinux.org/task/59699
link: https://github.com/NixOS/nixpkgs/issues/45165

Cc: stable@vger.kernel.org # v4.18+
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-input.c

@@ -1582,6 +1582,7 @@ static struct hid_input *hidinput_allocate(struct hid_device *hid,
 	input_dev->dev.parent = &hid->dev;
 
 	hidinput->input = input_dev;
+	hidinput->application = application;
 	list_add_tail(&hidinput->list, &hid->inputs);
 
 	INIT_LIST_HEAD(&hidinput->reports);
@@ -1677,8 +1678,7 @@ static struct hid_input *hidinput_match_application(struct hid_report *report)
 	struct hid_input *hidinput;
 
 	list_for_each_entry(hidinput, &hid->inputs, list) {
-		if (hidinput->report &&
-		    hidinput->report->application == report->application)
+		if (hidinput->application == report->application)
 			return hidinput;
 	}
 

drivers/hid/hid-multitouch.c

@@ -1697,6 +1697,9 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	 */
 	hdev->quirks |= HID_QUIRK_INPUT_PER_APP;
 
+	if (id->group != HID_GROUP_MULTITOUCH_WIN_8)
+		hdev->quirks |= HID_QUIRK_MULTI_INPUT;
+
 	timer_setup(&td->release_timer, mt_expired_timeout, 0);
 
 	ret = hid_parse(hdev);

include/linux/hid.h

@@ -526,6 +526,7 @@ struct hid_input {
 	const char *name;
 	bool registered;
 	struct list_head reports;	/* the list of reports */
+	unsigned int application;	/* application usage for this input */
 };
 
 enum hid_type {