Re: USB Lenovo ThinkPad Compact Keyboard has fn_lock inverted

[Jamie Lentin <jm@lentin.co.uk>]

On 2022-11-11 17:06, Josh Triplett wrote:
> I have an external ThinkPad USB keyboard:
> 
> $ lsusb | grep -i keyboard
> Bus 003 Device 022: ID 17ef:6047 Lenovo ThinkPad Compact Keyboard with
> TrackPoint
> 
> The Linux kernel exposes a fn_lock attribute in sysfs for this 
> keyboard:
> 
> $ cat
> sys/devices/pci0000:00/0000:00:14.0/usb3/3-5/3-5.4/3-5.4.3/3-5.4.3:1.1/0003:17EF:6047.000F/fn_lock
> 1
> 
> However, this attribute appears inverted for this particular keyboard:
> it seems to be 1 when FnLock is *disabled* and 0 when FnLock is
> *enabled*. In order to enable FnLock, I have to write 0 to this file.

Under Windows the default actions of the Function keys are the media 
keys, i.e. pressing F1 is Mute. Fn-"Mute" is F1, or enabling Fn-Lock & 
"Mute". That's why when /fn_lock is 1, the Mute key is F1.

With keyboards built into Thinkpads there's a BIOS setting to invert the 
behaviour of Fn-Lock (and thus have Fn keys by default), as well as 
swapping Fn<->Ctrl, but there's no equivalent option for the external 
keyboards.

What's the wrong way around here is hid-lenovo assumes that you want 
Fn-Lock on when connecting to the keyboard, not off. My assumption at 
the time was that whilst it's different to how the keyboard behaves 
under Windows, it'd be a more useful default.

> (Also, separately from that, it would be nice if the kernel could 
> handle
> fn_lock toggling *internally*, rather than expecting userspace to do 
> it.
> As far as I can tell, it does handle similar things for some keyboards,
> but not this one.)

Agreed. This was something I looked into when I was adding support for 
the keyboards. For yours it's a pretty trivial addition, but for the USB 
variant you can't send the command in the middle of the USB interrupt 
receiving the keypress, solving this seemed to require quite a lot of 
boilerplate for what would have been pretty trivial in userland.

Of course, It's very easily possible that I missed something, or there's 
a helper to do this sort of thing that now exists.

Cheers,