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

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Message-ID: <175826715682.18450.2507719983975659600@lain.khirnov.net>
Date: Fri, 19 Sep 2025 09:32:36 +0200
From:  Anton Khirnov <anton@...rnov.net>
To:  "Mario Limonciello (AMD) (kernel.org)" <superm1@...nel.org>
Cc:  Dmitry Torokhov <dmitry.torokhov@...il.com>,
 Corentin Chary <corentin.chary@...il.com>, "Luke D. Jones" <luke@...nes.dev>,
 Hans de Goede <hansg@...nel.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-input@...r.kernel.org
Subject:  Re: [PATCH v2 1/2] Input: allocate a keycode for Fn+space

Hi Mario,
Quoting Mario Limonciello (AMD) (kernel.org) (2025-09-19 07:36:31)
> 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@...rnov.net>
> >> ---
> >>   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?

Unfortunately I removed Windows from this machine right after buying it,
and reinstalling it would be too invasive. I did ask someone to test on
a different Asus laptop running Windows, the key did not seem to do
anything.

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

Fn+F7 toggles keyboard backlight on this laptop, so probably not. I'm
willing to believe it's a leftover from older hardware where it did do
something and they just forgot to disable it.

Cheers,
-- 
Anton Khirnov