Re: fn-key issue with hid_apple and keychron keyboards

[Hans de Goede <hdegoede@redhat.com>]

Hi Bastian,

On 5/17/21 9:46 AM, Bastian Venthur wrote:
> Hello Hans,
> 
> I'm writing you because apparently you provided the patch [1] for Linux "Disable Fn-key key-re-mapping on clone keyboards" -- which seems related to a bug I've found with Keychron C1 keyboard.
> 
> I'm really sorry if you're not the right contact for those kind of issues, and would be very happy if you could point me to the correct ones.

It is usually a good idea to at least Cc the relevant linux mailinglist on
questions like this. I've added the linux-input list to the Cc now.

> I recently got a Keychron C1 keyboard (but I gather, other Keyboards from this company are affected as well). The keyboard has a physical switch for "Windows" and "Mac" modes, however in both cases the kernel recognizes it as an Apple keyboard and loads the "hid-apple" module. However it does *not* recognize the 'Fn' key and disables it. But the keyboard has one and I have to enable it manually either via:
> 
> # as root:
> echo 2 > /sys/module/hid_apple/parameters/fnmode
> 
> or permanently:
> 
> options hid_apple fnmode=2
> in /etc/modprobe.d/hid_apple.conf
> 
> Without this, I cannot use the Function-keys, they will always be used as Multimedia-keys, regardless if you press Fn + F1 or not.
> 
> Here's the relevant dmesg output when i plug the keyboard in.
> 
> [    6.234069] apple 0003:05AC:024F.0004: input,hidraw3: USB HID v1.11 Keyboard [Keychron Keychron C1] on usb-0000:06:00.4-1.2.1.2/input0
> [    6.234261] apple 0003:05AC:024F.0005: Fn key not found (Apple Wireless Keyboard clone?), disabling Fn key handling
> [    6.294181] apple 0003:05AC:024F.0005: input,hidraw4: USB HID v1.11 Keyboard [Keychron Keychron C1] on usb-0000:06:00.4-1.2.1.2/input1

Ok, so the keyboard presents itself as 2 interfaces. and the "Fn key not found" message
is only being printed for the second interface. So I guess that the trouble F1-F12 keys
are actually coming out of the first interface (the 0003:05AC:024F.0004 device above).

What my patch does it completely disables the fnmode handling, similar to setting the
fnmode parameter to 0, but unlike my (Maxxter KB-BT-001 Bluetooth keyboard) "clone" your
keyboard does actually advertise a Mac style Fn key in its descriptors, at least for the
first interface so it is treated as a standard Mac keyboard where the non Fn behavior of
the F-keys is to send the multimedia events. Normally pressing Fn + F1 - F-12 should then
result in the kernel actually sending F1-F12 and setting fnmode=2 should just invert when
you need to press Fn.

Basically the way the actual mac keyboards work is the simply always send F1 - F12 events
and a separate Fn event and leave it up to the OS to translate this to either plain
F1 - F12 or to the multimedia codes. Where as normal keyboards handle the Fn press
internally and actually send different "scancodes" over the wire to the computer when
Fn + F1 - F12 is pressed.

But if I understand you correctly then the Fn translation hid-apple is doing to make
things work as expected with Mac keyboards is not working for you, IOW with fnmode=1
pressing Fn + F1 does not result in F1 being send, correct ?  This means that your
keyboard behaves more like a normal keyboard instead of as an apple keyboard.

I also wonder if the Fn key sends any events at all (or if it is fully handled internally)...

> I have no idea how to fix this, but I can provide additional information if needed.

Please become root ("sudo su -") and then do:

/sys/kernel/debug/hid/0003:05AC:024F.*/rdesc > Keychron-C1-rdesc

And attach the generated Keychron-C1-rdesc file to your next email.

Also please as root run:

sudo evemu-record

And then select the device belonging to your keyboard and press F1, Fn and Fn + F1,
please repeat this for all input devices belonging to your keyboard and then
copy and paste the output of each run into your next email.

Regards,

Hans