linux-kernel - Re: [PATCH] x86/Mouse: thinkpad_acpi/Trackpoint: Trackpoint Doubletap handling

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Message-Id: <4ad6e1e1-aca8-4774-aa4a-60edccaa6d0e@app.fastmail.com>
Date: Mon, 30 Jun 2025 05:42:45 +0900
From: "Mark Pearson" <mpearson-lenovo@...ebb.ca>
To: "Dmitry Torokhov" <dmitry.torokhov@...il.com>,
 "Vishnu Sankar" <vishnuocv@...il.com>
Cc: pali@...nel.org, "Henrique de Moraes Holschuh" <hmh@....eng.br>,
 hansg@...nel.org,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 tglx@...utronix.de, mingo@...nel.org, jon_xie@...art.com, jay_lee@...art.com,
 zhoubinbin@...ngson.cn, linux-input@...r.kernel.org,
 linux-kernel@...r.kernel.org, ibm-acpi-devel@...ts.sourceforge.net,
 "platform-driver-x86@...r.kernel.org" <platform-driver-x86@...r.kernel.org>,
 "Vishnu Sankar" <vsankar@...ovo.com>
Subject: Re: [PATCH] x86/Mouse: thinkpad_acpi/Trackpoint: Trackpoint Doubletap handling

Hi Dmitry,

On Fri, Jun 27, 2025, at 2:14 PM, Dmitry Torokhov wrote:
> Hi Vishnu,
>
> On Fri, Jun 20, 2025 at 09:42:08AM +0900, Vishnu Sankar wrote:
>> Newer ThinkPads have a doubletap feature that needs to be turned
>> ON/OFF via the trackpoint registers.
>> Systems released from 2023 have doubletap disabled by default and
>> need the feature enabling to be useful.
>> 
>> This patch introduces support for exposing and controlling the
>> trackpoint doubletap feature via a sysfs attribute.
>> /sys/devices/platform/thinkpad_acpi/tp_doubletap
>> This can be toggled by an "enable" or a "disable".
>> 
>> With this implemented we can remove the masking of events, and rely on
>> HW control instead, when the feature is disabled.
>> 
>> Note - Early Thinkpads (pre 2015) used the same register for hysteris
>> control, Check the FW IDs to make sure these are not affected.
>> 
>> trackpoint.h is moved to linux/input/.
>
> No, please keep everything private to trackpoint.c and do not involve
> thinkpad_acpi driver. By doing so you are introducing unwanted
> dependencies (for both module loading, driver initialization, and
> operation) and unsafe use of non-owned pointers/dangling pointers, etc.
>

Do you have recommendations on how to handle this case then?

This is a Thinkpad specific feature and hence the logic for involving thinkpad_acpi. There are Thinkpad hotkeys that will enable/disable the trackpoint doubletap feature - so there is some linkage. I'm not sure how to avoid that.

Is there a cleaner way to do this that you'd recommend we look at using? It's a feature (albeit a minor one) on the laptops that we'd like to make available to Linux users.

Mark