[PATCH] Input: mms114: don't report 0 pressure while still tracking contact(s)

In the middle of a sliding gesture, we manage to have events
that look like that:
    Event: time 1571859641.595517, -------------- SYN_REPORT ------------
    Event: time 1571859641.606593, type 3 (EV_ABS), code 54 (ABS_MT_POSITION_Y), value 1193
    Event: time 1571859641.606593, type 3 (EV_ABS), code 48 (ABS_MT_TOUCH_MAJOR), value 21
    Event: time 1571859641.606593, type 3 (EV_ABS), code 58 (ABS_MT_PRESSURE), value 0
    Event: time 1571859641.606593, type 3 (EV_ABS), code 1 (ABS_Y), value 1193
    Event: time 1571859641.606593, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 0
    Event: time 1571859641.606593, -------------- SYN_REPORT ------------

In such cases, we still have a valid ABS_MT_TRACKING_ID along
with an ABS_MT_TOUCH_MAJOR that is > 0, which both indicates
that the sliding is still in progress.

However in Documentation/input/multi-touch-protocol.rst, we
have:
    ABS_MT_PRESSURE
        The pressure, in arbitrary units, on the contact
        area. May be used instead of TOUCH and WIDTH for
        pressure-based devices or any device with a spatial
        signal intensity distribution.

Because of that userspace may consider an ABS_MT_PRESSURE
of 0 as an indication that the sliding stopped. This has
side effects such as making it difficult to unlock the
screen under Android.

This fix was tested on the following devices:
- GT-I9300 with a glass screen protection
- GT-I9300 without any screen protection
- GT-N7105 with a glass screen protection

Reported-by: Javi Ferrer <redacted>
Signed-off-by: Denis 'GNUtoo' Carikli <redacted>
---
 drivers/input/touchscreen/mms114.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/input/touchscreen/mms114.c b/drivers/input/touchscreen/mms114.c
index 2ef1adaed9af..adc18cd9a437 100644
--- a/drivers/input/touchscreen/mms114.c
+++ b/drivers/input/touchscreen/mms114.c

@@ -183,7 +183,10 @@ static void mms114_process_mt(struct mms114_data *data, struct mms114_touch *tou
 	if (touch->pressed) {
 		touchscreen_report_pos(input_dev, &data->props, x, y, true);
 		input_report_abs(input_dev, ABS_MT_TOUCH_MAJOR, touch->width);
-		input_report_abs(input_dev, ABS_MT_PRESSURE, touch->strength);
+		if (touch->strength) {
+			input_report_abs(input_dev, ABS_MT_PRESSURE,
+					 touch->strength);
+		}
 	}
 }
 

-- 
2.26.2