linux-kernel - Re: [REGRESSION] wrong coord from Thinkpad TrackPoint since 6.2 kernel

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Message-ID: <874jq3q52i.wl-tiwai@suse.de>
Date:   Wed, 29 Mar 2023 11:28:53 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Takashi Iwai <tiwai@...e.de>,
        Pali Rohár <pali@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        regressions@...ts.linux.dev, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] wrong coord from Thinkpad TrackPoint since 6.2 kernel

On Wed, 29 Mar 2023 11:22:18 +0200,
Hans de Goede wrote:
> 
> Hi Takashi,
> 
> On 3/29/23 10:16, Takashi Iwai wrote:
> > Hi,
> > 
> > we've received a bug report about Thinkpad TrackPoint (ALPS DualPoint
> > Stick) on 6.2 kernel:
> >   https://bugzilla.opensuse.org/show_bug.cgi?id=1209805
> > 
> > The device reports the wrong values as the movements, e.g. sometimes a
> > value such as 255, 254 or -255 is returned while usually it should be
> > a smaller value like -1 or 2.
> > 
> > The evtest on 6.2.x kernel shows the wrong values like:
> > 
> > Event: time 1680037542.898747, type 2 (EV_REL), code 0 (REL_X), value 255
> > Event: time 1680037542.898747, -------------- SYN_REPORT ------------
> > Event: time 1680037543.145196, type 2 (EV_REL), code 0 (REL_X), value 1
> > Event: time 1680037543.145196, -------------- SYN_REPORT ------------
> > Event: time 1680037543.175087, type 2 (EV_REL), code 1 (REL_Y), value -255
> > Event: time 1680037543.175087, -------------- SYN_REPORT ------------
> > Event: time 1680037543.185421, type 2 (EV_REL), code 0 (REL_X), value 1
> > Event: time 1680037543.185421, type 2 (EV_REL), code 1 (REL_Y), value -255
> > Event: time 1680037543.185421, -------------- SYN_REPORT ------------
> > 
> > while 6.1.x kernel shows the correct values like:
> > 
> > Event: time 1680037386.318058, type 2 (EV_REL), code 0 (REL_X), value -1
> > Event: time 1680037386.318058, type 2 (EV_REL), code 1 (REL_Y), value -1
> > Event: time 1680037386.318058, -------------- SYN_REPORT ------------
> > Event: time 1680037386.328087, type 2 (EV_REL), code 0 (REL_X), value -1
> > Event: time 1680037386.328087, type 2 (EV_REL), code 1 (REL_Y), value -1
> > Event: time 1680037386.328087, -------------- SYN_REPORT ------------
> > Event: time 1680037386.338046, type 2 (EV_REL), code 0 (REL_X), value -1
> > Event: time 1680037386.338046, type 2 (EV_REL), code 1 (REL_Y), value -2
> > Event: time 1680037386.338046, -------------- SYN_REPORT ------------
> >   
> > I couldn't see any relevant changes in alps.c between those versions,
> > so this is likely a breakage in a lower layer.
> > 
> > Could you guys take a look?
> 
> I believe this is caused by the kernel now using -funsigned-char
> everywhere and this should be fixed by this commit:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git/commit/?h=for-linus&id=754ff5060daf5a1cf4474eff9b4edeb6c17ef7ab

Ah, that makes sense!

I'll build a test kernel with this fix and ask the reporter for
testing.

> And there is a similar issue in the focaltech touchpad driver:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git/commit/?h=for-linus&id=8980f190947ba29f23110408e712444884b74251
> 
> Dmitry, since this is hitting 6.2 users, perhaps you can send
> a pull-req for your current for-linus branch to get the fix
> on its way to stable ?

That'll be great.


Thanks!

Takashi