[PATCH] HID: logitech-hidpp: fix hi-res scroll for Bolt-connected MX Master

[Rafael Passos <rafael@rcpassos.me>]

The new added support for Logitech HID++ caused this mouse to
scroll too far for each tic when using the USB dongle (Bolt).
Previously, this mouse was handled as hid_generic over the Bold
connection, and logitech-hidpp when over Bluetooth.

Cause:
Over the Bolt receiver, the mouse reports  are forwarded over the generic
interface 1, instead of the new HID++ child device. The generic hid does
now know about the hi-res scrolling used by the HID++.
In my tests, I discovered this mouse has a multiplier factor of 15. This
multiplier is only handled by the logitech-hidpp driver. When piped to
hid_generic, the "hi-res" value was piped to a "low-res" field, making
the scroll unbearable.

The fix routes the wheel using the HID++, so the ticks are scaled by the
multiplier and correctly reported as a hi-res event.

I also had to move the hidpp_is_bolt_child function up, to use it in the
hidpp_connect_event function, where the gate for
hidpp_initialize_hires_scroll function lives.

Tested with:
- Logitech MX Master 3S (mouse) via Bolt receiver and Bluetooth.

Fixes: 022eb347ff3a ("HID: logitech: add Bolt receiver support for Logitech HID++ devices")
Signed-off-by: Rafael Passos <rafael@rcpassos.me>
---

Hi,
I decided to send this patch as soon as I made it work, to try to make
it into this fix cycle.

I do not have other devices to test this with.
It would *be great* to have other users testing this.

Lastly, I decided to make all the changes in a single patch. 
But I can break it up if asked.

Thanks,
Rafael


 drivers/hid/hid-logitech-hidpp.c | 47 ++++++++++++++++++++++----------
 1 file changed, 32 insertions(+), 15 deletions(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index 1504de32b1c84..960543bfd5ea1 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -3900,6 +3900,19 @@ static int hidpp10_consumer_keys_raw_event(struct hidpp_device *hidpp,
 	return 1;
 }
 
+static bool hidpp_is_bolt_child(struct hid_device *hdev)
+{
+	struct device *parent = hdev->dev.parent;
+	struct hid_device *receiver_hdev;
+
+	if (!parent)
+		return false;
+
+	receiver_hdev = to_hid_device(parent);
+	return receiver_hdev->vendor == USB_VENDOR_ID_LOGITECH &&
+	       receiver_hdev->product == USB_DEVICE_ID_LOGITECH_BOLT_RECEIVER;
+}
+
 /* -------------------------------------------------------------------------- */
 /* High-resolution scroll wheels                                              */
 /* -------------------------------------------------------------------------- */
@@ -3910,7 +3923,9 @@ static int hi_res_scroll_enable(struct hidpp_device *hidpp)
 	u8 multiplier = 1;
 
 	if (hidpp->capabilities & HIDPP_CAPABILITY_HIDPP20_HI_RES_WHEEL) {
-		ret = hidpp_hrw_set_wheel_mode(hidpp, false, true, false);
+		bool use_hidpp = hidpp_is_bolt_child(hidpp->hid_dev);
+
+		ret = hidpp_hrw_set_wheel_mode(hidpp, false, true, use_hidpp);
 		if (ret == 0)
 			ret = hidpp_hrw_get_wheel_capability(hidpp, &multiplier);
 	} else if (hidpp->capabilities & HIDPP_CAPABILITY_HIDPP20_HI_RES_SCROLL) {
@@ -3998,6 +4013,19 @@ static int hidpp20_hires_wheel_raw_event(struct hidpp_device *hidpp,
 		return 1;
 	}
 
+	/* wheel movement event: 16-bit signed delta in HID++ ticks */
+	if ((data[3] & 0xf0) == 0x00 && size >= 7 && hidpp->input &&
+	    hidpp->vertical_wheel_counter.wheel_multiplier) {
+		s16 delta = get_unaligned_be16(&data[5]);
+
+		if (delta) {
+			hidpp_scroll_counter_handle_scroll(hidpp->input,
+				&hidpp->vertical_wheel_counter, delta);
+			input_sync(hidpp->input);
+		}
+		return 1;
+	}
+
 	return 0;
 }
 
@@ -4405,19 +4433,6 @@ static int hidpp_initialize_battery(struct hidpp_device *hidpp)
 	return ret;
 }
 
-static bool hidpp_is_bolt_child(struct hid_device *hdev)
-{
-	struct device *parent = hdev->dev.parent;
-	struct hid_device *receiver_hdev;
-
-	if (!parent)
-		return false;
-
-	receiver_hdev = to_hid_device(parent);
-	return receiver_hdev->vendor == USB_VENDOR_ID_LOGITECH &&
-	       receiver_hdev->product == USB_DEVICE_ID_LOGITECH_BOLT_RECEIVER;
-}
-
 static int hidpp_bolt_init(struct hidpp_device *hidpp)
 {
 	struct hid_device *hdev = hidpp->hid_dev;
@@ -4579,7 +4594,9 @@ static void hidpp_connect_event(struct work_struct *work)
 	}
 
 	hidpp_initialize_battery(hidpp);
-	if (!hid_is_usb(hidpp->hid_dev))
+
+	if (!hid_is_usb(hidpp->hid_dev) ||
+	    hidpp_is_bolt_child(hidpp->hid_dev))
 		hidpp_initialize_hires_scroll(hidpp);
 
 	/* forward current battery state */
-- 
2.55.0