The HID descriptor of many of Wacom's touch input devices include a "Confidence" usage that signals if a particular touch collection contains useful data. The driver does not look at this flag, however, which causes even invalid contacts to be reported to userspace. A lucky combination of kernel event filtering and device behavior (specifically: contact ID 0 == invalid, contact ID >0 == valid; and order all data so that all valid contacts are reported before any invalid contacts) spare most devices from any visibly-bad behavior.

The DTH-2452 is one example of an unlucky device that misbehaves. It uses ID 0 for both the first valid contact and all invalid contacts. Because we report both the valid and invalid contacts, the kernel reports that contact 0 first goes down (valid) and then goes up (invalid) in every report. This causes ~100 clicks per second simply by touching the screen.

This patch inroduces new `confidence` flag in our `hid_data` structure. The value is initially set to `true` at the start of a report and can be set to `false` if an invalid touch usage is seen.

Link: https://github.com/linuxwacom/input-wacom/issues/270 Fixes: f8b6a74719b5 ("HID: wacom: generic: Support multiple tools per report") Signed-off-by: Jason Gerecke jason.gerecke@wacom.com Tested-by: Joshua Dickens joshua.dickens@wacom.com Cc: stable@vger.kernel.org --- drivers/hid/wacom_wac.c | 8 +++++++- drivers/hid/wacom_wac.h | 1 + 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c index 33a6908995b1..2a4cc39962e7 100644 --- a/drivers/hid/wacom_wac.c +++ b/drivers/hid/wacom_wac.c @@ -2603,6 +2603,9 @@ static void wacom_wac_finger_event(struct hid_device *hdev, return;

switch (equivalent_usage) { + case HID_DG_CONFIDENCE: + wacom_wac->hid_data.confidence = value; + break; case HID_GD_X: wacom_wac->hid_data.x = value; break; @@ -2635,7 +2638,8 @@ static void wacom_wac_finger_event(struct hid_device *hdev, }

if (usage->usage_index + 1 == field->report_count) { - if (equivalent_usage == wacom_wac->hid_data.last_slot_field) + if (equivalent_usage == wacom_wac->hid_data.last_slot_field && + wacom_wac->hid_data.confidence) wacom_wac_finger_slot(wacom_wac, wacom_wac->touch_input); } } @@ -2653,6 +2657,8 @@ static void wacom_wac_finger_pre_report(struct hid_device *hdev,

wacom_wac->is_invalid_bt_frame = false;

+ hid_data->confidence = true; + for (i = 0; i < report->maxfield; i++) { struct hid_field *field = report->field[i]; int j; diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h index 8b2d4e5b2303..466b62cc16dc 100644 --- a/drivers/hid/wacom_wac.h +++ b/drivers/hid/wacom_wac.h @@ -301,6 +301,7 @@ struct hid_data { bool barrelswitch; bool barrelswitch2; bool serialhi; + bool confidence; int x; int y; int pressure;