On Mon, 8 Nov 2021, Jason Gerecke wrote:
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
Applied, thanks Jason.