I'm using a laptop with the Elan touchpad (04f3:0c1a), which is handled in 4.18 Linux kernel by i2c-hid module.
Unfortunately my kern.log and syslog gets flooded with "incomplete report" messages whenever I use the touchpad which fills the log very, very quickly (dozens messages per second).
I did not investigated why the report are incomplete, but simply reduced number of the same messages the module spits out.
In the original source file I replaced dev_err with dev_err_once. And I'm importing hid-ids.h from the same directory
(the file was copied from the source tree of 4.18 kernel).
To build the module I needed linux-headers-4.18.0-2-amd64 and linux-kbuild-4.18.
Then it just
cd 4.18.0 # use the version of your kernel
make
make install # (which will just copy the .ko file to the `/lib/modules/...
Use target reload to uninstall current module and install a new one.