Re: [BUG] ThinkPad T490 Synaptics TM3471-020 input lag and missed taps with SMBus/RMI4

Re: [BUG] ThinkPad T490 Synaptics TM3471-020 input lag and missed taps with SMBus/RMI4

[Lovekesh Solanki]

Hi thanks for the report,

On Fri, Oct 30, 2026 at 06:10:50PM -0700, Eduardo Henrique Teixeira wrote:
> Potentially related upstream change:
> 
> Commit a961417c5ae77bbb728a23d9577ecd8f4d8a4b5a
> 
> “Input: synaptics - add LEN205b entry to smbus_pnp_ids for ThinkPad T490”
> 
> https://lkml.iu.edu/2609.2/11883.html
This was only added because the original reporter confirmed Intertouch
worked well on their device.

You said it happens more frequently while charging, so I wonder if PM is
involved.

Could you try reproducing after warm and cold boots?
And also with disabling runtime PM for the device?

Regards,
Lovekesh

Re: [BUG] ThinkPad T490 Synaptics TM3471-020 input lag and missed taps with SMBus/RMI4

[Lovekesh Solanki]

On Tue, Nov 03, 2026 at 04:07:48AM +0000, Eduardo Henrique Teixeira wrote:
> Regarding your questions, I can confirm that the problem persists after
> both warm boots (restarting the laptop) and cold boots (completely shutting
> it down and powering it back on). I haven’t noticed any significant
> difference between these scenarios.
> 
> 
> At first, I suspected some kind of electromagnetic interference or a
> hardware-related issue with the power supply. I even tested a brand-new,
> genuine Lenovo charger that I had kept as a spare, but the behavior
> remained unchanged.
> 
> I believe my initial impression was influenced by how I normally use the
> laptop. I rarely use its built-in touchpad while charging because, at home,
> I usually connect the laptop to a docking station with an external keyboard
> and mouse.
> 
> However, after performing additional tests, I confirmed that the issue
> occurs consistently both while charging and while running on battery power.

Okay, thanks for testing.

> I understand that the original reporter confirmed InterTouch was working
> correctly on their device, so perhaps there is some hardware or firmware
> variation between T490 units that would explain the different results.
> 
> I haven’t yet tested disabling runtime power management specifically, but I
> can perform that test if it would help further investigate the issue.
>

I can't think of any other reason why this only breaks on your machine.
Things look same between the original report and yours.
Maybe Dmitry would have any idea what could cause an issue like this.

Could you also test with runtime PM disabled while rmi4 debug enabled?
(boot via rmi_core.debug_flags=1)
Wonder if the device is getting suspended between touches which might
explain the lag.

Regards,
Lovekesh

Re: [BUG] ThinkPad T490 Synaptics TM3471-020 input lag and missed taps with SMBus/RMI4

[Dmitry Torokhov]

Hi Eduardo,

On Fri, Oct 30, 2026 at 06:10:50PM -0700, Eduardo Henrique Teixeira wrote:
> I would like to report a possible issue with Synaptics InterTouch
> (SMBus/RMI4) on the Lenovo ThinkPad T490.
>
> Hardware:
>
>    - Model: Lenovo ThinkPad T490 (20N3S5DU1N)
>    - Touchpad: Synaptics TM3471-020
>    - Firmware ID: 3972349
>    - BIOS: 1.85
>    - Distribution: Ubuntu
>    - Kernel: 7.3.0-10-generic
>
> Symptoms:
>
> The touchpad exhibits noticeable delays when detecting finger contact,
> sometimes perceived as approximately 200–500 ms before pointer movement
> begins.
>
> Short taps frequently fail to register as mouse clicks. Longer touches are
> more likely to be recognized.

Dmitry Mikushin (CCed) recently fixed a performance bottleneck on
Synaptics TM3471 over SMBus where rmi_f12 was reading the entire
79-byte F12 data packet on every attention interrupt (requiring three
SMBus block reads and ~17.4 ms per frame, capping the report rate at
~43 Hz), even though only the first 32 bytes (Data1) are used.

Could you please test his two rmi_f12 patches (now in the input next
branch) that limit the F12 read to Data1 (~7.3 ms, ~65 Hz) and see if
they resolve the input lag and missed taps on your T490:

https://lore.kernel.org/linux-input/20261026142648.2567233-2-dmitry@kernelgen.org/
https://lore.kernel.org/linux-input/20261026142648.2567233-3-dmitry@kernelgen.org/

Thanks.

-- 
Dmitry