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

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

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