Why does libinput randomly calls my touchpad "SynPS/2 Synaptics" or "Synaptics TM2722-001"?

[Lyude Paul]

Just so folks know: I happen to have experience with this part of the
linux kernel (it's not a libinput bug) so I handled this offlist and
redirected Ottavio to the right place to ask for support ♥

On Tue, 2024-04-23 at 15:12 +0100, Ottavio Caruso wrote:
> Hi,
> 
> $ sudo X -version
> 
> X.Org X Server 1.21.1.7
> X Protocol Version 11, Revision 0
> Current Operating System: Linux t440 6.1.0-20-amd64 #1 SMP 
> PREEMPT_DYNAMIC Debian 6.1.85-1 (2024-04-11) x86_64
> Kernel command line: BOOT_IMAGE=/boot/vmlinuz-6.1.0-20-amd64 
> root=UUID=42a17f43-89bb-4523-952f-b8d97bcb4a30 ro quiet
> xorg-server 2:21.1.7-3+deb12u7 (https://www.debian.org/support)
> Current version of pixman: 0.42.2
> 
> $ xinput --version
> xinput version 1.6.3
> XI version on server: 2.4
> 
> 
> 
> On my old-ish Thinkpad T440, libinput alternatively calls my touchpad
> "SynPS/2 Synaptics" or "Synaptics TM2722-001".
> 
> $ grep Synaptics  /var/log/messages
> Nov 26 09:12:38 t440 kernel: [18070.908478] psmouse serio1:
> synaptics: 
> serio: Synaptics pass-through port at isa0060/serio1/input0
> Nov 26 09:12:38 t440 kernel: [18070.947812] input: SynPS/2 Synaptics 
> TouchPad as /devices/platform/i8042/serio1/input/input35
> Nov 26 20:33:19 t440 kernel: [27221.274488] rmi4_f01 rmi4-00.fn01:
> found 
> RMI device, manufacturer: Synaptics, product: TM2722-001, fw id: 0
> Nov 26 20:33:19 t440 kernel: [27221.314747] input: Synaptics TM2722-
> 001 
> as /devices/pci0000:00/0000:00:1f.3/i2c-0/0-002c/rmi4-
> 00/input/input39
> Nov 27 19:28:05 t440 kernel: [    6.327297] psmouse serio1:
> synaptics: 
> serio: Synaptics pass-through port at isa0060/serio1/input0
> Nov 27 19:28:05 t440 kernel: [    6.366655] input: SynPS/2 Synaptics 
> TouchPad as /devices/platform/i8042/serio1/input/input2
> 
> This without even rebooting or suspending the laptop.
> 
> I have some scripts that disable or enable the touchpad (especially
> when 
> I use the mouse) and I have to use tricks to accommodate this.
> 
> Why does this happen in the first place? How can I troubleshoot it?
> 
> Thanks.
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat