linux-kernel - Re: Requesting your attention and expertise regarding a Tablet/Kernel issue

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Message-ID: <CAO-hwJLjtjdr2gtrOWJFPZ-38YzKB8XfhDKWf_2jUPeiaP3EcA@mail.gmail.com>
Date:   Wed, 8 Nov 2023 10:34:52 +0100
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     José Expósito <jose.exposito89@...il.com>
Cc:     Eric GOUYER <folays@...il.com>,
        Illia Ostapyshyn <ostapyshyn@....uni-hannover.de>,
        David Revoy <davidrevoy@...tonmail.com>, jkosina@...e.cz,
        jason.gerecke@...om.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Requesting your attention and expertise regarding a Tablet/Kernel issue

On Wed, Nov 8, 2023 at 10:23 AM José Expósito <jose.exposito89@...il.com> wrote:
>
> Hi Benjamin,
>
> On Wed, Nov 08, 2023 at 10:04:30AM +0100, Benjamin Tissoires wrote:
[...]
> >
> > >
> > > So, the behavior probably breaks the specs, but sincerely I'm happy to
> > > have the "eraser" button independent of the "rubber eraser", which
> > > makes the stylus a somewhat 4-buttons stylus (tip, button1, button2,
> > > rubber), and I would like to keep this.
> >
> > Yes, and I'd like to keep it that way, even if 6.6 and 6.5.8
> > apparently broke it.
> >
> > So, to me:
> > - 276e14e6c3993317257e1787e93b7166fbc30905 is wrong: this is a
> > firmware bug (reporting invert through eraser) and should not be
> > tackled at the generic level, thus it should be reverted
> > - both of these tablets are forwarding the useful information, but not
> > correctly, which confuses the kernel
> > - I should now be able to write regression tests
> > - I should be able to provide HID-BPF fixes for those tablets so that
> > we can keep them working with or without
> > 276e14e6c3993317257e1787e93b7166fbc30905
> > reverted (hopefully)
> > - problem is I still don't have the mechanics to integrate the HID-BPF
> > fixes directly in the kernel tree, so maybe I'll have to write a
> > driver for XP-Pen while these internals are set (it shouldn't
> > interfere with the HID-BPF out of the tree).
>
> I already added support for a few XP-Pen devices on the UCLogic driver
> and I was planning to start working on this one during the weekend in
> my DIGImend fork (to simplify testing).
>
> Let me know if you prefer to add it yourself or if you want me to ping
> you in the DIGImend discussion.
>

So far, I really have to work on this now. It's a good use case for
HID-BPF and it's a regression that I'd like to be fixed ASAP.
I'd appreciate any reviews :)

Also, good to know that I can probably piggyback on hid-uclogic for
fixing those 2 devices in the kernel.

Cheers,
Benjamin