Function keys do not work
If your F<num> keys do not work, this is probably because the kernel driver for the keyboard has defaulted to using the media keys and requiring you to use the Fn key to get to the F<num> keys. To change the behavior temporarily, append 2 to /sys/module/hid_apple/parameters/fnmode.
# echo 2 > /sys/module/hid_apple/parameters/fnmode
To make the change permanent, set the hid_apple fnmode option to 2:
/etc/modprobe.d/hid_apple.conf
options hid_apple fnmode=2
To apply the change to your initial ramdisk, in your mkinitcpio configuration (usually /etc/mkinitcpio.conf), make sure you either have modconf included in the HOOKS variable or /etc/modprobe.d/hid_apple.conf in the FILES variable. You would then need to regenerate the initramfs.
if you need more help I can help you... I compile my own kernels and everything else in linux myself.
I don't personally run Arch as a main distro, I run Gentoo, but they are related and I do get a lot of help for my own problems from Arch wikis. I have run nearly every distribution of linux. What distribution are you running on that mac? Ubuntu? Yellow Dog? Debian? (can't remember all the others that support mac (those may be old ppc versions of mac and not the new intel))
source :
https://wiki.archlinux.org/index.php/Apple_Keyboard