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HID: wacom: Use "Confidence" flag to prevent reporting invalid contacts

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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: f8b6a74719 ("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>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Jason Gerecke 2021-11-08 16:31:01 -08:00 committed by Jiri Kosina
parent 304dd3680b
commit 7fb0413baa
2 changed files with 8 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/hid/wacom_wac.c
View File

@ -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;

1
drivers/hid/wacom_wac.h
View File

@ -301,6 +301,7 @@ struct hid_data {
bool barrelswitch;
bool barrelswitch2;
bool serialhi;
bool confidence;
int x;
int y;
int pressure;