Starting with the 5.2 kernel instead we actually look at the devices behind the receiver. This allows us to provide battery monitoring support and to have per device quirks, like device specific HID-code to evdev-code mappings where necessary. Until now device specific quirks where not possible because the receivers have a generic product-id which is the same independent of the device behind the receiver.
The per device key-mapping is especially important for 27MHz wireless devices, these use the same HID-code for Fn + F1 to Fn + F12 for all devices, but the markings on the keys differ per model. Sofar it was impossible for Linux to get the mapping for this right, but now that we have per device product-ids for the devices behind the receiver we can finally fix this. As is the case with other devices with vendor specific mappings, the actual mapping is done in userspace through hwdb.
If you have a 27 MHz device (often using this receiver, keyboard marked as canada 210 or canada 310 at the bottom). Please give 5.2 a try. Download the latest 60-keyboard.hwdb file and place it in /lib/udev/hwdb.d (replacing the existing file) and then run "sudo udevadm hwdb --update", before booting into the 5.2 kernel. Then run "sudo evemu-record" select your keyboard and try Fn + F1 to Fn + F12 and any other special keys. If any keys do not work, edit 60-keyboard.hwdb, search for Logitech and add an entry for your keyboard, see the existing Logitech entries. After editing you need to re-run "sudo udevadm hwdb --update", followed by "sudo udevadm trigger" for the changes to take effect. Once you have a working entry, submit a pull-req to systemd to get the changes upstream. If you need any help drop me an email.
We still have some old code for the generic HID emulation for 27 MHz receivers with a product-id of c50c, these should work fine with the new code, but we've been unable to test this. I would really like to move the c50c id over to the new code and remove all the old code. If you've a 27 MHz Logitech device, please run lsusb, if your device has a product-id of c50c and you are willing to test, please drop me an email.
Likewise I suspect that 2.4GHz receivers with a product-id of c531 should work fine with the new support for non-unifying 2.4 GHz receivers, if you have one of those also please drop me an email.