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

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Message-ID: <c49cf225-c508-4e23-8786-5110a166d7c4@kernel.org>
Date: Fri, 19 Sep 2025 00:36:31 -0500
From: "Mario Limonciello (AMD) (kernel.org)" <superm1@...nel.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>,
 Anton Khirnov <anton@...rnov.net>
Cc: 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

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?

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