[PATCH 0/1] Force I2C bus freq to 100KHz for ELAN06FA touchpad

[Randolph Ha <rha051117@gmail.com>]

In my device (Lenovo V15 G4 IRU) it appears that, even with the latest
BIOS update, the ACPI tables do not specify that the ELAN06FA touchpad
only works properly at a 100KHz I2C frequency, with other frequencies
causing excessive smoothing to be applied intermittently. On some
busses (designware-i2c), the default frequency is 400KHz.

This smoothing causes the touchpad to be unusable under Linux, and the
support request I filed with Lenovo was ignored. After adding a device
ID check to force the frequency to 100KHz for this touchpad, the
excessive smoothing disappears. As a similar patch was previously
accepted for the Silead MSSL1680 touchscreen in [1], I hope this patch
can be added into the kernel as well.

Additional Notes:
1. I speculate that this issue was caused by the touchpad firmware
interpreting the higher clock frequency as noise, since the smoothing
effect is similar to that caused by using a noisy third-party charger.
2. Based on the coil whine emitted by my laptop, it appears as though
the driver is ran at 100KHz under Windows by default as well, so I
believe this is the fix, not a workaround.
3. This fix should also apply to the Lenovo V15 G4 AMN and the Ideapad
Slim 3 15IAH8, but I do not have the devices to confirm.

[1]: Commit 7574c0db2e68c ("i2c: acpi: Force bus speed to 400KHz if a
Silead touchscreen is present")

Randolph Ha (1):
  Force ELAN06FA touchpad I2C bus freq to 100KHz

 drivers/i2c/i2c-core-acpi.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

-- 
2.47.1