HID: magicmouse: properly account for scroll movement in state

Before this change, sequential scroll events would take a variable
amount of movement due to incorrect accounting. This change ensures all
scroll movements require a deterministic touch movement for an action to
occur.

Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Acked-by: Michael Poole <mdpoole@troilus.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/hid/hid-magicmouse.c b/drivers/hid/hid-magicmouse.c
index 4c4a79c760a2..f44aaf21e1e2 100644
--- a/drivers/hid/hid-magicmouse.c
+++ b/drivers/hid/hid-magicmouse.c
@@ -189,7 +189,8 @@ static void magicmouse_emit_touch(struct magicmouse_sc *msc, int raw_id, u8 *tda
                 case TOUCH_STATE_DRAG:
                         step = step / accel_profile[msc->scroll_accel];
                         if (step != 0) {
-                                msc->touches[id].scroll_y = y;
+                                msc->touches[id].scroll_y -=
+                                        step * accel_profile[msc->scroll_accel];
                                 msc->scroll_jiffies = now;
                                 input_report_rel(input, REL_WHEEL, step);
                         }