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

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Message-ID: <20250629205148.l2etpceayuzmhzph@pali>
Date: Sun, 29 Jun 2025 22:51:48 +0200
From: Pali Rohár <pali@...nel.org>
To: Mark Pearson <mpearson-lenovo@...ebb.ca>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Vishnu Sankar <vishnuocv@...il.com>,
	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

On Monday 30 June 2025 05:42:45 Mark Pearson wrote:
> 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

Hello, I do not know what is doubletap and patch description does not
explain it. But for laptop / mouse interface, I'm just giving example
that dell-laptop.c for some particular laptop can enable/disable
touchpad led and uses PS/2 interface for it. See touchpad_led_init().
I do not know if it is ideal or preferred solution, just writing to let
you know, maybe it can be useful.