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 [off-list ref] wrote:

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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.

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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.

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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