[PATCH 0/1] HID: apple: Properly handle function keys on Keychron keyboards

[Bryan Cain <bryancain3@gmail.com>]

Hi,

As the new owner of a Keychron C1 keyboard, I recently found this thread from
this mailing list (linux-input):

https://lore.kernel.org/all/897e57a9-38d8-c05f-ceed-01d486f02726@redhat.com/T/

To summarize the findings in that thread:
* Keychron keyboards (C-series and K-series) use the vendor:product IDs from a
  2009 Apple keyboard. When set to "Mac" mode, they actually do behave like
  that device, but in "Windows" mode, the Fn key doesn't generate a scancode,
  making it impossible to use F1-F12 when the fnmode parameter is set to its
  default value of 1.
* The universally accepted "fix" among Keychron owners online is to set
  fnmode=2 in /etc/modprobe.d/hid_apple.conf.
  (See https://gist.github.com/andrebrait/961cefe730f4a2c41f57911e6195e444)
* Keychron devices can be distinguished from Apple ones by the USB manufacturer
  string, but it's impossible for the kernel to programatically detect whether
  a Keychron keyboard is in "Windows" or "Mac" mode.

The thread arrives at a conclusion I agree with: that fnmode=2 should be the
default behavior for Keychron keyboards. But no one has actually implemented
this change yet, so I decided to do it myself.

My patch sets the default fnmode to the new value of 3, which behaves like
fnmode=2 for Keychron keyboards, and like the previous default of fnmode=1
for real Apple keyboards and any non-Keychron clones. This should produce
sensible behavior in all cases, including the corner case where someone plugs
a Keychron keyboard into their MacBook.

This change does mean that Keychron function keys in "Mac" mode won't default
to Apple-like behavior, but even in that case, both the Fn and non-Fn versions
of the keys are still usable. And as Bastian Venthur said in the thread linked
above, there's no particular reason for a user to expect Apple-like behavior
when using a non-Apple device with a non-Apple operating system.

This is my first time contributing to the kernel, so please let me know if I
need to do anything differently. Also, I don't have an Apple keyboard on hand
to test with, so I'd appreciate if someone could test my patch with one to
verify that their function key behavior is unchanged.

Regards,
Bryan


Bryan Cain (1):
  HID: apple: Properly handle function keys on Keychron keyboards

 drivers/hid/hid-apple.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

-- 
2.25.1