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Subject[PATCH v2 2/5] Create a utility class for counting scroll events
Date
To avoid code duplication, this class counts high-resolution scroll
movements and emits the legacy low-resolution events when appropriate.
Drivers should be able to create one instance for each scroll wheel that
they need to handle.

Signed-off-by: Harry Cutts <hcutts@chromium.org>
---

Changes in v2: None

drivers/hid/hid-input.c | 45 +++++++++++++++++++++++++++++++++++++++++
include/linux/hid.h | 28 +++++++++++++++++++++++++
2 files changed, 73 insertions(+)

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);
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 834e6461a690..037e37b0b0e6 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -1138,6 +1138,34 @@ static inline u32 hid_report_len(struct hid_report *report)
int hid_report_raw_event(struct hid_device *hid, int type, u8 *data, u32 size,
int interrupt);

+
+/**
+ * struct hid_scroll_counter - Utility class for processing high-resolution
+ * scroll events.
+ * @dev: the input device for which events should be reported.
+ * @microns_per_hi_res_unit: the amount moved by the user's finger for each
+ * high-resolution unit reported by the mouse, in
+ * microns.
+ * @resolution_multiplier: the wheel's resolution in high-resolution mode as a
+ * multiple of its lower resolution. For example, if
+ * moving the wheel by one "notch" would result in a
+ * value of 1 in low-resolution mode but 8 in
+ * high-resolution, the multiplier is 8.
+ * @remainder: counts the number of high-resolution units moved since the last
+ * low-resolution event (REL_WHEEL or REL_HWHEEL) was sent. Should
+ * only be used by class methods.
+ */
+struct hid_scroll_counter {
+ struct input_dev *dev;
+ int microns_per_hi_res_unit;
+ int resolution_multiplier;
+
+ int remainder;
+};
+
+void hid_scroll_counter_handle_scroll(struct hid_scroll_counter *counter,
+ int hi_res_value);
+
/* HID quirks API */
unsigned long hid_lookup_quirk(const struct hid_device *hdev);
int hid_quirks_init(char **quirks_param, __u16 bus, int count);
--
2.19.0.rc0.228.g281dcd1b4d0-goog
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