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

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Date:   Fri, 18 Mar 2022 14:07:40 +0100
From:   José Expósito <jose.exposito89@...il.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     linux-input@...r.kernel.org,
        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: Re: [REGRESSION] Right touchpad button disabled on Dell 7750

Hi Takashi,

Thanks for reporting the regression here.

On Fri, Mar 18, 2022 at 12:42:31PM +0100, Takashi Iwai 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.
> 
> Is this check really correct in general?  Or do we need some
> device-specific quirk?

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.

Thanks,
Jose

[1] https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/726#note_1303623