High CPU usage on RMI4 interrupt with Synaptics touchpad

High CPU usage on RMI4 interrupt with Synaptics touchpad

[Mike Murdoch]

Greetings,

I'm running kernel 5.4.7 on a recently acquired a Lenovo Thinkpad X1 
Extreme Gen 2. It has a Synaptics touchpad and a Elan trackpoint being 
passed through.

When the psmouse module loads normally, I get a message indicating it 
can support a different bus:

psmouse serio1: synaptics: Your touchpad (PNP: LEN0402 PNP0f13) says it 
can support a different bus. If i2c-hid and hid-rmi are not used, you 
might want to try setting psmouse.synaptics_intertouch to 1 and report 
this to linux-input@vger.kernel.org.

Upon reloading the module with synaptics_intertouch=1, the touchpad and 
trackpoint return, here's the kernel log:

rmi4_smbus 5-002c: registering SMbus-connected sensor
rmi4_f34 rmi4-02.fn34: rmi_f34v7_probe: Unrecognized bootloader version
rmi4_f34: probe of rmi4-02.fn34 failed with error -22
rmi4_f01 rmi4-02.fn01: found RMI device, manufacturer: Synaptics, 
product: TM3512-010, fw id: 2956703
input: Synaptics TM3512-010 as /devices/rmi4-02/input/input41
serio: RMI4 PS/2 pass-through port at rmi4-02.fn03
psmouse serio6: trackpoint: Elan TrackPoint firmware: 0x11, buttons: 3/3
input: TPPS/2 Elan TrackPoint as 
/devices/rmi4-02/rmi4-02.fn03/serio6/input/input42

However I notice that cursor movement with the touchpad is now quite 
choppy and causes a LOT of CPU usage on irq/165-rmi4_sm. Clearly 
something is not working as intended. Curiously, I think I managed to 
get RMI4 to work properly *once*, but cannot reproduce it anymore. Might 
have been a fluke or my imagination too...

I'll be glad to help figure this out.

Thanks and best regards,
- Mike