linux-kernel - Re: [PATCH 1/4] Input: Add trackpoint doubletap and system debug info keycodes

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Date: Tue, 9 Apr 2024 12:16:04 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: Mark Pearson <mpearson-lenovo@...ebb.ca>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Henrique de Moraes Holschuh <hmh@....eng.br>,
 ibm-acpi-devel@...ts.sourceforge.net,
 "platform-driver-x86@...r.kernel.org" <platform-driver-x86@...r.kernel.org>,
 linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
 Nitin Joshi1 <njoshi1@...ovo.com>, Vishnu Sankar <vsankar@...ovo.com>,
 Peter Hutterer <peter.hutterer@...hat.com>
Subject: Re: [PATCH 1/4] Input: Add trackpoint doubletap and system debug info
 keycodes

Hi Dmitry,

On 4/9/24 2:00 AM, Mark Pearson wrote:
> Hi Dmitry
> 
> On Mon, Apr 8, 2024, at 7:31 PM, Dmitry Torokhov wrote:
>> Hi Mark,
>>
>> On Sun, Mar 24, 2024 at 05:07:58PM -0400, Mark Pearson wrote:
>>> Add support for new input events on Lenovo laptops that need exporting to
>>> user space.
>>>
>>> Lenovo trackpoints are adding the ability to generate a doubletap event.
>>> Add a new keycode to allow this to be used by userspace.
>>
>> What is the intended meaning of this keycode? How does it differ from
>> the driver sending BTN_LEFT press/release twice?
> 
> Double tapping on the trackpoint is a unique event - it's not the same as BTN_LEFT twice. The BIOS will send a new ACPI event for it and it's not meant to be the same as mouse button clicks.

To extend a bit on this, this double-tap event is not reported through
the PS/2 trackpoint interface at all. Instead it is reported to
the OS by the ACPI hotkey notifier, which is used to report various
multi-media hotkeys and things like that, this is handled by
the thinkpad_apci driver which sofar only reports key-presses.

So there is no BTN_LEFT to report twice and if we add a BTN_LEFT
then we end up with an input_device which has a bunch of KEYs
+ BTN_LEFT but no abs/rel axis which will just confuse userspace.

We could add a second input_device which looks like a mouse
but only ever reports BTN_LEFT double-clicks I guess, but as
Mark said the intention is for this double-tap to work more
like a hotkey then a double click. Also note that regular
taps on the trackstick do nothing. Clicking the mouse buttons
of the stick involves pressing separate physical buttons between
the trackpad and the keyboard and those are reported over
the same PS/2 port as the relative motion events from the stick.

Regards,

Hans