Hello. I first sent this email to kernel-mentors, but I got no response. So I am sending it again here. I wrote a driver for the Corsair K90 keyboard, it is my first kernel development and I have a few questions about how to properly do a few things (mainly interactions with the user space). The Corsair Vengeance K90 is a mechanical keyboard with a backlight, macro keys (G1 to G18) and some other special keys (macro recording, profile switching, changing the light level or disabling the "windows logo" keys). The macro playback can be switched between hardware or software (from the driver not a key). Using the generic HID driver, the macro keys and special keys send wrong key code or no key code at all (because of the HID usage code used by the keyboard). The source for my driver can be found at this address: https://github.com/cvuchener/k90-linux-driver . It solves the problem of the generic driver and add some handling of the other features (see the README for more details). So, my questions are about: - Macro keys For handling the macro keys from a software, they need to send some keycodes but I have no idea what to use. Currently I use F keys above 12 and some MISC buttons and a parameter for changing that (at load time). Are there 18 keycodes reserved for custom uses? It would also be possible to send no keycode at all and use a specific software listening to the hidraw or hiddev devices, but I think it would be better to be able to use a generic software. - Backlight I chose to use a led class device to manage the backlight. It seems to work fine but when unregistering the driver, the light is set to 0. The keyboard remembers the previous light level and so nothing should be done when registering or unregistering the driver. Is the led class the right class for that? or am I using it wrong? - Sending the macro profiles to the keyboard I created a "profile" branch on my git repo for adding binary attributes used for sending macro data to the keyboard. But I am not sure it is a good idea, it may be better to leave that to the user space. Any other comment is welcome. Thanks, Clément