On Wed, 19 Apr 2017, Jason Gerecke wrote:
> It apears that devices designed around Wacom's G11 chipset (e.g. Lenovo
> ThinkPad Yoga 260, Lenovo ThinkPad X1 Yoga, Dell XPS 12 9250, Dell Venue
> 8 Pro 5855, etc.) suffer from a common issue in their HID descriptors.
> The logical maximum is not updated for the "Contact Identifier" usage,
> leaving it as just "1" despite these devices being capable of tracking
> far more touches.
>
> Commit 60a221869803 began ignoring usages with out-of-range values,
> causing problems for devices based on this chipset. Touches after
> the first will have an out-of-range Contact Identifier, and ignoring
> that usage will cause the kernel to incorrectly slot each finger's
> events (along with all the knock-on userspace effects that entails).
>
> This commit checks for these buggy descriptors and updates the maximum
> where required. Prior chipsets have used "255" as the maximum (and the
> G11, at least, doesn't seem to actually use IDs outside the range of
> 1..CONTACTMAX) so continue using this value.
>
> Signed-off-by: Jason Gerecke <jason.gerecke@xxxxxxxxx>
> ---
> Jiri, please add this to your 'for-4.11/upstream-fixes' branch since
> commit 60a221869803 was introduced in 4.11 and leaving this unaddressed
> could impact a wide variety of tablet PCs.
60a221869803 has actually been present since 4.10-rc1, therefore I've
added
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 60a221869803 ("HID: wacom: generic: add support for touchring")
to make sure all the affected stables will eventually get it.
--
Jiri Kosina
SUSE Labs
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