[PATCH] Input: zinitix: iterate contact slots by finger count

[Thanh Nguyen <thanhnguyxn07@gmail.com>]

On affected devices (for example Samsung A3 2015), the value in
touch_event.finger_mask appears to behave as a count of reported slots
rather than a bitmask. Using for_each_set_bit() can then skip valid
contacts and break multitouch gestures.

Keep filtering by SUB_BIT_EXIST to avoid reporting shadow contacts, but
iterate from slot 0 up to min(finger_mask, MAX_SUPPORTED_FINGER_NUM).
This follows the maintainer feedback to treat the field as a possible
count while preserving the anti-shadow check.

Fixes: e941dc13fd37 ("Input: zinitix - do not report shadow fingers")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=221278
Signed-off-by: Thanh Nguyen <thanhnguyxn07@gmail.com>
---
v2:
 - Address maintainer feedback: do not revert e941dc13fd37.
 - Keep SUB_BIT_EXIST filtering to avoid shadow contacts.
 - Treat finger_mask as a slot-count bound and iterate 0..min(mask, max).

 drivers/input/touchscreen/zinitix.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/input/touchscreen/zinitix.c b/drivers/input/touchscreen/zinitix.c
index 716d6fa60..a2edae7df 100644
--- a/drivers/input/touchscreen/zinitix.c
+++ b/drivers/input/touchscreen/zinitix.c
@@ -471,7 +471,8 @@ static irqreturn_t zinitix_ts_irq_handler(int irq, void *bt541_handler)
 	}
 
 	finger_mask = touch_event.finger_mask;
-	for_each_set_bit(i, &finger_mask, MAX_SUPPORTED_FINGER_NUM) {
+	for (i = 0; i < min_t(unsigned long, finger_mask,
+			MAX_SUPPORTED_FINGER_NUM); i++) {
 		const struct point_coord *p = &touch_event.point_coord[i];
 
 		/* Only process contacts that are actually reported */
-- 
2.51.0.windows.2