Writing a driver for the Corsair K90 keyboard

[Clément Vuchener]

It looks like no one had the answers to these questions. Is there a 
better place to ask them?

> 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