Re: [PATCH v2 1/2] Input: allocate a keycode for Fn+space

[Mario Limonciello (AMD) (kernel.org)]

On 9/19/2025 12:12 AM, Dmitry Torokhov wrote:
> Hi Anton,
>
> On Mon, Jul 14, 2025 at 05:07:57PM +0200, Anton Khirnov wrote:
> > The Asus ExpertBook B9 laptop sends a WMI event when Fn+space is
> > pressed. Since I could not find any information on what this combination
> > is intended to do on this or any other Asus laptop, allocate a
> > KEY_FN_SPACE keycode for it.
> >
> > Signed-off-by: Anton Khirnov <anton@xxxxxxxxxxx>
> > ---
> >   include/uapi/linux/input-event-codes.h | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
> > index 3b2524e4b667..a49b0782fd8a 100644
> > --- a/include/uapi/linux/input-event-codes.h
> > +++ b/include/uapi/linux/input-event-codes.h
> > @@ -548,6 +548,7 @@
> >   #define KEY_FN_S		0x1e3
> >   #define KEY_FN_B		0x1e4
> >   #define KEY_FN_RIGHT_SHIFT	0x1e5
> > +#define KEY_FN_SPACE		0x1e6
>
> I'd rather we did not add more codes with no defined meaning. I regret
> that we have KEY_FN_* (with the exception of KEY_FN itself). Since
> nobody knows what this key is supposed to do maybe map it to
> KEY_RESERVED and whoever wants to use it can map it to a concrete key
> code via udev?
>
> Thanks.

Any chance you can look at Windows and see what the key actually does 
when you have the matching OEM software installed?

I've seen a bunch of laptops that FN+SPACE turns on/off keyboard 
backlight.  Maybe that's what it does.