[PATCH v3 1/5] Input: zinitix - check all available fingers for every touch event

[Kaustabh Chakraborty <kauschluss@disroot.org>]

When this initial driver was first added to tree, that is, in commit
26822652c85e ("Input: add zinitix touchscreen driver"), the touch_event
struct had a field called finger_cnt. It was supposed to report how many
fingers are touching the screen.

But then, in commit e941dc13fd37 ("Input: zinitix - do not report shadow
fingers"), some touchscreens reportedly exposed a bit mask for the
fingers, instead of the count. So the code was changed to bitwise
iteration.

With my testing on the ZT7548 touchscreen of the Galaxy J6, I find the
former to be true. This shows that there's two valid methods depending
on what hardware the driver is made to work on.

One solution is to implement both methods, and use some flag to select
between the two. However, this introduces more implementation overhead,
and a possibility of regression on devices the driver is expected to work.

Instead, unconditionally check all fingers. The finger_mask field is now
left unused, thus serving as padding bytes in the struct. For each
finger, zinitix_report_finger() is called if the status reports the
SUB_BIT_EXIST bit, so phantom fingers are not going to be a thing.

Moreover, the android driver [1] does exactly that, so it's a tried
method of implementation.

Link: https://android.googlesource.com/kernel/bcm/+/23d376ef33aa4c500a5ea24a290f029d5f8e2de3/drivers/input/touchscreen/zinitix_touch.c#1942 [1]
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
---
 drivers/input/touchscreen/zinitix.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/input/touchscreen/zinitix.c b/drivers/input/touchscreen/zinitix.c
index 0c36765bd79f..3421b8ffb19b 100644
--- a/drivers/input/touchscreen/zinitix.c
+++ b/drivers/input/touchscreen/zinitix.c
@@ -445,7 +445,6 @@ static irqreturn_t zinitix_ts_irq_handler(int irq, void *bt541_handler)
 	struct bt541_ts_data *bt541 = bt541_handler;
 	struct i2c_client *client = bt541->client;
 	struct touch_event touch_event;
-	unsigned long finger_mask;
 	__le16 icon_events;
 	int error;
 	int i;
@@ -470,8 +469,7 @@ static irqreturn_t zinitix_ts_irq_handler(int irq, void *bt541_handler)
 		zinitix_report_keys(bt541, le16_to_cpu(icon_events));
 	}
 
-	finger_mask = touch_event.finger_mask;
-	for_each_set_bit(i, &finger_mask, MAX_SUPPORTED_FINGER_NUM) {
+	for (i = 0; i < MAX_SUPPORTED_FINGER_NUM; i++) {
 		const struct point_coord *p = &touch_event.point_coord[i];
 
 		/* Only process contacts that are actually reported */

-- 
2.54.0