Re: [PATCH] HID: wacom: Use "Confidence" flag to prevent reporting invalid contacts

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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@xxxxxxxxx>
> Tested-by: Joshua Dickens <joshua.dickens@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>

Applied, thanks Jason.

-- 
Jiri Kosina
SUSE Labs




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