[PATCH] HID: lenovo: Add middleclick_workaround sysfs knob for cptkbd

[Mikhail Khvainitski <me@xxxxxxxxxxxxxxx>]

Built-in firmware of cptkbd handles scrolling by itself (when middle
button is pressed) but with issues: it does not support horizontal and
hi-res scrolling and upon middle button release it sends middle button
click even if there was a scrolling event. Commit 3cb5ff0220e3 ("HID:
lenovo: Hide middle-button press until release") workarounds last
issue but it's impossible to workaround scrolling-related issues
without firmware modification.

Likely, Dennis Schneider has reverse engineered the firmware and
provided an instruction on how to patch it [1]. However,
aforementioned workaround prevents userspace (libinput) from knowing
exact moment when middle button has been pressed down and performing
"On-Button scrolling". This commit makes it possible to disable this
workaround by sysfs knob.

Link: https://hohlerde.org/rauch/en/elektronik/projekte/tpkbd-fix/ [1]

Signed-off-by: Mikhail Khvainitski <me@xxxxxxxxxxxxxxx>
---
 drivers/hid/hid-lenovo.c | 84 +++++++++++++++++++++++++++++-----------
 1 file changed, 62 insertions(+), 22 deletions(-)

diff --git a/drivers/hid/hid-lenovo.c b/drivers/hid/hid-lenovo.c
index 44763c0da444..8993fa1ce66a 100644
--- a/drivers/hid/hid-lenovo.c
+++ b/drivers/hid/hid-lenovo.c
@@ -53,6 +53,7 @@ struct lenovo_drvdata {
 	int press_speed;
 	u8 middlebutton_state; /* 0:Up, 1:Down (undecided), 2:Scrolling */
 	bool fn_lock;
+	bool middleclick_workaround_cptkbd;
 };
 
 #define map_key_clear(c) hid_map_usage_clear(hi, usage, bit, max, EV_KEY, (c))
@@ -603,6 +604,36 @@ static ssize_t attr_sensitivity_store_cptkbd(struct device *dev,
 	return count;
 }
 
+static ssize_t attr_middleclick_workaround_show_cptkbd(struct device *dev,
+		struct device_attribute *attr,
+		char *buf)
+{
+	struct hid_device *hdev = to_hid_device(dev);
+	struct lenovo_drvdata *cptkbd_data = hid_get_drvdata(hdev);
+
+	return snprintf(buf, PAGE_SIZE, "%u\n",
+		cptkbd_data->middleclick_workaround_cptkbd);
+}
+
+static ssize_t attr_middleclick_workaround_store_cptkbd(struct device *dev,
+		struct device_attribute *attr,
+		const char *buf,
+		size_t count)
+{
+	struct hid_device *hdev = to_hid_device(dev);
+	struct lenovo_drvdata *cptkbd_data = hid_get_drvdata(hdev);
+	int value;
+
+	if (kstrtoint(buf, 10, &value))
+		return -EINVAL;
+	if (value < 0 || value > 1)
+		return -EINVAL;
+
+	cptkbd_data->middleclick_workaround_cptkbd = !!value;
+
+	return count;
+}
+
 
 static struct device_attribute dev_attr_fn_lock =
 	__ATTR(fn_lock, S_IWUSR | S_IRUGO,
@@ -614,10 +645,16 @@ static struct device_attribute dev_attr_sensitivity_cptkbd =
 			attr_sensitivity_show_cptkbd,
 			attr_sensitivity_store_cptkbd);
 
+static struct device_attribute dev_attr_middleclick_workaround_cptkbd =
+	__ATTR(middleclick_workaround, S_IWUSR | S_IRUGO,
+			attr_middleclick_workaround_show_cptkbd,
+			attr_middleclick_workaround_store_cptkbd);
+
 
 static struct attribute *lenovo_attributes_cptkbd[] = {
 	&dev_attr_fn_lock.attr,
 	&dev_attr_sensitivity_cptkbd.attr,
+	&dev_attr_middleclick_workaround_cptkbd.attr,
 	NULL
 };
 
@@ -668,31 +705,33 @@ static int lenovo_event_cptkbd(struct hid_device *hdev,
 {
 	struct lenovo_drvdata *cptkbd_data = hid_get_drvdata(hdev);
 
-	/* "wheel" scroll events */
-	if (usage->type == EV_REL && (usage->code == REL_WHEEL ||
-			usage->code == REL_HWHEEL)) {
-		/* Scroll events disable middle-click event */
-		cptkbd_data->middlebutton_state = 2;
-		return 0;
-	}
+	if (cptkbd_data->middleclick_workaround_cptkbd) {
+		/* "wheel" scroll events */
+		if (usage->type == EV_REL && (usage->code == REL_WHEEL ||
+				usage->code == REL_HWHEEL)) {
+			/* Scroll events disable middle-click event */
+			cptkbd_data->middlebutton_state = 2;
+			return 0;
+		}
 
-	/* Middle click events */
-	if (usage->type == EV_KEY && usage->code == BTN_MIDDLE) {
-		if (value == 1) {
-			cptkbd_data->middlebutton_state = 1;
-		} else if (value == 0) {
-			if (cptkbd_data->middlebutton_state == 1) {
-				/* No scrolling inbetween, send middle-click */
-				input_event(field->hidinput->input,
-					EV_KEY, BTN_MIDDLE, 1);
-				input_sync(field->hidinput->input);
-				input_event(field->hidinput->input,
-					EV_KEY, BTN_MIDDLE, 0);
-				input_sync(field->hidinput->input);
+		/* Middle click events */
+		if (usage->type == EV_KEY && usage->code == BTN_MIDDLE) {
+			if (value == 1) {
+				cptkbd_data->middlebutton_state = 1;
+			} else if (value == 0) {
+				if (cptkbd_data->middlebutton_state == 1) {
+					/* No scrolling inbetween, send middle-click */
+					input_event(field->hidinput->input,
+						EV_KEY, BTN_MIDDLE, 1);
+					input_sync(field->hidinput->input);
+					input_event(field->hidinput->input,
+						EV_KEY, BTN_MIDDLE, 0);
+					input_sync(field->hidinput->input);
+				}
+				cptkbd_data->middlebutton_state = 0;
 			}
-			cptkbd_data->middlebutton_state = 0;
+			return 1;
 		}
-		return 1;
 	}
 
 	if (usage->type == EV_KEY && usage->code == KEY_FN_ESC && value == 1) {
@@ -1146,6 +1185,7 @@ static int lenovo_probe_cptkbd(struct hid_device *hdev)
 	cptkbd_data->middlebutton_state = 0;
 	cptkbd_data->fn_lock = true;
 	cptkbd_data->sensitivity = 0x05;
+	cptkbd_data->middleclick_workaround_cptkbd = true;
 	lenovo_features_set_cptkbd(hdev);
 
 	ret = sysfs_create_group(&hdev->dev.kobj, &lenovo_attr_group_cptkbd);
-- 
2.42.0