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

[Takashi Iwai <tiwai@suse.de>]

On Wed, 29 Mar 2023 11:28:53 +0200,
Takashi Iwai wrote:
> 
> 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 it's confirmed that the commit above fixes the problem indeed.


thanks,

Takashi