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

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Date:   Fri, 18 Mar 2022 12:42:31 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     linux-input@...r.kernel.org
Cc:     José Expósito <jose.exposito89@...il.com>,
        Peter Hutterer <peter.hutterer@...-t.net>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Jiri Kosina <jkosina@...e.cz>, stable@...r.kernel.org,
        regressions@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: [REGRESSION] Right touchpad button disabled on Dell 7750

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.

Is this check really correct in general?  Or do we need some
device-specific quirk?

thanks,

Takashi