HID: 3m: Correct touchscreen emulation

The current code sometimes misses to report the last BTN_TOUCH event
when multiple fingers are lifted simultaneously.  With the
introduction of MT slots, the tracking id is available to determine
the oldest active contact. Use this information to simplify and
correct the touchscreen emulation logic.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Acked-by: Stéphane Chatty <chatty@enac.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-3m-pct.c

@@ -37,15 +37,14 @@ MODULE_LICENSE("GPL");
 struct mmm_finger {
 	__s32 x, y, w, h;
 	__u16 id;
-	__u8 rank;
 	bool prev_touch;
 	bool touch, valid;
 };
 
 struct mmm_data {
 	struct mmm_finger f[MAX_SLOTS];
 	__u16 id;
-	__u8 curid, num;
+	__u8 curid;
 	__u8 nexp, nreal;
 	bool touch, valid;
 };
@@ -156,13 +155,7 @@ static int mmm_input_mapped(struct hid_device *hdev, struct hid_input *hi,
 static void mmm_filter_event(struct mmm_data *md, struct input_dev *input)
 {
 	struct mmm_finger *oldest = 0;
-	bool pressed = false, released = false;
 	int i;
-
-	/*
-	 * we need to iterate on all fingers to decide if we have a press
-	 * or a release event in our touchscreen emulation.
-	 */
 	for (i = 0; i < MAX_SLOTS; ++i) {
 		struct mmm_finger *f = &md->f[i];
 		if (!f->valid) {
@@ -183,34 +176,11 @@ static void mmm_filter_event(struct mmm_data *md, struct input_dev *input)
 						wide ? f->w : f->h);
 			input_event(input, EV_ABS, ABS_MT_TOUCH_MINOR,
 						wide ? f->h : f->w);
-			/*
-			 * touchscreen emulation: maintain the age rank
-			 * of this finger, decide if we have a press
-			 */
-			if (f->rank == 0) {
-				f->rank = ++(md->num);
-				if (f->rank == 1)
-					pressed = true;
-			}
-			if (f->rank == 1)
+			/* touchscreen emulation: pick the oldest contact */
+			if (!oldest || ((f->id - oldest->id) & (SHRT_MAX + 1)))
 				oldest = f;
 		} else {
 			/* this finger took off the screen */
-			/* touchscreen emulation: maintain age rank of others */
-			int j;
-
-			for (j = 0; j < 10; ++j) {
-				struct mmm_finger *g = &md->f[j];
-				if (g->rank > f->rank) {
-					g->rank--;
-					if (g->rank == 1)
-						oldest = g;
-				}
-			}
-			f->rank = 0;
-			--(md->num);
-			if (md->num == 0)
-				released = true;
 			input_event(input, EV_ABS, ABS_MT_TRACKING_ID, -1);
 		}
 		f->prev_touch = f->touch;
@@ -219,11 +189,10 @@ static void mmm_filter_event(struct mmm_data *md, struct input_dev *input)
 
 	/* touchscreen emulation */
 	if (oldest) {
-		if (pressed)
-			input_event(input, EV_KEY, BTN_TOUCH, 1);
+		input_event(input, EV_KEY, BTN_TOUCH, 1);
 		input_event(input, EV_ABS, ABS_X, oldest->x);
 		input_event(input, EV_ABS, ABS_Y, oldest->y);
-	} else if (released) {
+	} else {
 		input_event(input, EV_KEY, BTN_TOUCH, 0);
 	}
 	input_sync(input);