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authorHarry Cutts <hcutts@chromium.org>2018-08-30 14:56:19 -0700
committerJiri Kosina <jkosina@suse.cz>2018-09-05 10:12:07 +0200
commit1ff2e1a44e02d4bdbb9be67c7d9acc240a67141f (patch)
tree96129c381432acfcfe1638d06594d60fc3eb1c8d /drivers/hid/hid-input.c
parentaaf9978c3c0291ef3beaa97610bc9c3084656a85 (diff)
HID: input: Create a utility class for counting scroll events
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> Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'drivers/hid/hid-input.c')
-rw-r--r--drivers/hid/hid-input.c45
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);