1 files changed, 45 insertions, 0 deletions
diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 4e94ea3e280a..6e84e7b9afcb 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1826,3 +1826,48 @@ void hidinput_disconnect(struct hid_device *hid)
 }
 EXPORT_SYMBOL_GPL(hidinput_disconnect);
 
+/**
+ * hid_scroll_counter_handle_scroll() - Send high- and low-resolution scroll
+ *                                      events given a high-resolution wheel
+ *                                      movement.
+ * @counter: a hid_scroll_counter struct describing the wheel.
+ * @hi_res_value: the movement of the wheel, in the mouse's high-resolution
+ *                units.
+ *
+ * Given a high-resolution movement, this function converts the movement into
+ * microns and emits high-resolution scroll events for the input device. It also
+ * uses the multiplier from &struct hid_scroll_counter to emit low-resolution
+ * scroll events when appropriate for backwards-compatibility with userspace
+ * input libraries.
+ */
+void hid_scroll_counter_handle_scroll(struct hid_scroll_counter *counter,
+				      int hi_res_value)
+{
+	int low_res_scroll_amount;
+	/* Some wheels will rest 7/8ths of a notch from the previous notch
+	 * after slow movement, so we want the threshold for low-res events to
+	 * be in the middle of the notches (e.g. after 4/8ths) as opposed to on
+	 * the notches themselves (8/8ths).
+	 */
+	int threshold = counter->resolution_multiplier / 2;
+
+	input_report_rel(counter->dev, REL_WHEEL_HI_RES,
+			 hi_res_value * counter->microns_per_hi_res_unit);
+
+	counter->remainder += hi_res_value;
+	if (abs(counter->remainder) >= threshold) {
+		/* Add (or subtract) 1 because we want to trigger when the wheel
+		 * is half-way to the next notch (i.e. scroll 1 notch after a
+		 * 1/2 notch movement, 2 notches after a 1 1/2 notch movement,
+		 * etc.).
+		 */
+		low_res_scroll_amount =
+			counter->remainder / counter->resolution_multiplier
+			+ (hi_res_value > 0 ? 1 : -1);
+		input_report_rel(counter->dev, REL_WHEEL,
+				 low_res_scroll_amount);
+		counter->remainder -=
+			low_res_scroll_amount * counter->resolution_multiplier;
+	}
+}
+EXPORT_SYMBOL_GPL(hid_scroll_counter_handle_scroll);