On Tue, 3 Sep 2024, Gerecke, Jason wrote:
> From: Jason Gerecke <jason.gerecke@xxxxxxxxx>
>
> In ancient times, an off-by-one-nybble error resulted in the Wacom
> driver sending "mangled" tool IDs to userspace. This mangling behavior
> was later enshrined into a function so that devices using the then-new
> generic codepath could share the same broken behavior. The mangled IDs
> have not historically been a major problem for userspace since few
> applications care about the exact numeric value of the IDs. As long as
> the IDs were unique it didn't much matter. Some programs (cross-
> platform and remote-desktop applications in particular) /do/ rely on
> the IDs being correct, however.
>
> This patch rids the driver of the mangling behavior.
>
> Signed-off-by: Jason Gerecke <jason.gerecke@xxxxxxxxx>
> References: 493630b20389 ("Input: wacom - fix serial number handling on Cintiq 21UX2")
> References: 82527da319ee ("HID: wacom: Read and internally use corrected Intuos tool IDs")
> ---
> I'd like to get the opinion of the kernel maintainers on making a
> change like this at some point in the future. There are _very_ few
> userspace uses of these IDs (primarily: drivers, compositors, and
> tablet control panels) and my plan is to update those bits and then
> give some time for the changes to roll out to users before re-
> submitting this for real. I don't expect any kind of breakage since
> we'll be taking our time with the rollout and userspace needs to
> have handling for "unknown" IDs anyway (since Wacom periodically
> releases new pens).
As you are in control of the whole ecosystem anyway (because it's Wacom
specific), I don't see it as particularly problematic.
Thanks,
--
Jiri Kosina
SUSE Labs
