Extend device driver?

[greg@kroah.com (Greg KH)]

On Sat, Sep 10, 2016 at 08:58:07PM +0200, Pol Eyschen wrote:
> On 10/09/16 17:14, Greg KH wrote:
> > On Sat, Sep 10, 2016 at 04:41:34PM +0200, Pol Eyschen wrote:
> > > Hi everyone,
> > > 
> > > I want to implement some custom functions of my mouse (Madcatz RAT5) in
> > > Linux, e.g custom DPI-values. As this requires writing over USB to the
> > > firmware of the mouse I was thinking of writing a module to accomplish
> > > this. However I don't want to reimplement a whole mouse-driver,so I
> > > wanted to ask if there is a possibility of binding the device to 2
> > > modules or having my module extend usbhid, so that my module would only
> > > be used to perform these custom operations while usbhid stays in charge
> > > of the whole "mouse business".
> > 
> > Please just use the hidraw userspace driver/library instead, that way
> > you don't have to unbind the kernel driver and everything should work
> > just fine without having to touch the kernel at all.
> > 
> > Hope this helps,
> > 
> > greg k-h
> > 
> 
> I looked at hidraw, unfortunately it doesn't work for me, as the mouse
> expects control URBs with proprietary requests, hence my thought for a
> kernel module.

Ok, then yes, you need to have a separate kernel driver.  Look at one of
the many examples of this in the kernel already, this is quite common.

For specific questions about this, I suggest asking on the linux-input
mailing list, as that is where the developers of this code live.

good luck!

greg k-h