linux-kernel - Re: [REGRESSION] Right touchpad button disabled on Dell 7750

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Date:   Fri, 18 Mar 2022 15:28:24 +0100
From:   José Expósito <jose.exposito89@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Takashi Iwai <tiwai@...e.de>, linux-input@...r.kernel.org,
        Peter Hutterer <peter.hutterer@...-t.net>,
        Jiri Kosina <jkosina@...e.cz>, stable@...r.kernel.org,
        regressions@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] Right touchpad button disabled on Dell 7750

On Fri, Mar 18, 2022 at 03:06:55PM +0100, Benjamin Tissoires wrote:
> On Fri, Mar 18, 2022 at 2:11 PM Takashi Iwai <tiwai@...e.de> wrote:
> > > > Hi,
> > > >
> > > > we received a bug report about the regression of the touchpad on Dell
> > > > 7750 laptop, the right touchpad button is disabled on recent kernels:
> > > >   https://bugzilla.suse.com/show_bug.cgi?id=1197243
> > > >
> > > > Note that it's a physical button, not a virtual clickpad button.
> > > >
> > > > The regression seems introduced by the upstream commit
> > > > 37ef4c19b4c659926ce65a7ac709ceaefb211c40 ("Input: clear
> > > > BTN_RIGHT/MIDDLE on buttonpads") that was backported to stable 5.16.x
> > > > kernel.
> > > >
> > > > The device is managed by hid-multitouch driver, and the further
> > > > investigation revealed that it's rather an incorrectly recognized
> > > > buttonpad property; namely, ID_DG_BUTTONTYPE reports it being 0 =
> > > > clickable touchpad although it's not.  I built a test kernel to ignore
> > > > this check and it was confirmed to make the right button working again
> > > > by the reporter.
> 
> Yep, I came to the same conclusion this morning with the reporter of
> the libinput bug José was mentioning.
> 
> > > >
> > > > Is this check really correct in general?  Or do we need some
> > > > device-specific quirk?
> 
> The device firmware is clearly wrong here. It's the first time I see
> this failing like that and I hope this is just an isolated case.
> The device advertises itself as a buttonpad, when it's not.
> 
> However, the fact that it passed MS certification (even if I doubt
> Microsoft ever got that touchpad in their own hands) leads me to
> believe that the certification doesn't enforce that setting too much,
> and that we might see more devices coming in with that same bug.
> 
> To sum up, I am not happy that this commit introduced a regression
> that we can not work around in userspace: given that BTN_RIGHT gets
> removed from the device, all of the values are filtered out and
> userspace can not resolve that situation by itself.
> 
> I wish I had a better way of fixing this than having to quirk the device.
> 
> > >
> > > A couple of days ago another user with the same laptop (Dell Precision
> > > 7550 or 7750) emailed me to report the issue and I sent him a patch for
> > > testing.
> > >
> > > I he confirms that the patch works, I'll send it to the mailing list.
> > >
> > > I believe that your analysis of the regression is correct and I think
> > > that we'd need to add a quirk for the device.
> > >
> > > In case you want to have a look to the patch, I added it to this
> > > libinput [1] report.
> >
> > Great, I'll try to build and ask the reporter to test with the patch.
> >
> 
> As noticed on the libinput bug, I think the patch is wrong (not by a lot).
> We should base the class on MT_CLS_WIN8, not MT_CLS_DEFAULT.

Thanks for providing the right class Benjamin, I updated the patch:
https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/726#note_1303724
 
Jose