hidpp_scroll_counter_handle_scroll() doesn't expect a 0-value scroll event, it
gets interpreted as a negative scroll direction event. This can cause scroll
direction resets and thus broken scrolling.

Reported-and-tested-by: Aimo Metsälä <aimet...@outlook.com>
Signed-off-by: Peter Hutterer <peter.hutte...@who-t.net>
---
 drivers/hid/hid-logitech-hidpp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index 15ed6177a7a3..f040c8a7f9a9 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -2608,8 +2608,9 @@ static int m560_raw_event(struct hid_device *hdev, u8 
*data, int size)
                input_report_rel(mydata->input, REL_Y, v);
 
                v = hid_snto32(data[6], 8);
-               hidpp_scroll_counter_handle_scroll(
-                               &hidpp->vertical_wheel_counter, v);
+               if (v != 0)
+                       hidpp_scroll_counter_handle_scroll(
+                                       &hidpp->vertical_wheel_counter, v);
 
                input_sync(mydata->input);
        }
-- 
2.20.1

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