I'm not necessarily looking for a solution, although that would be great... mainly an explanation.
On a MacBook 1.1 using rEFInd boot manager, if I boot Mint 17 Cinnamon 32-bit via the Grub bootloader, my keyboard works fine. If instead, I use rEFInd to select the vmlinuz kernel (with EFIstub support) for Mint 17, the keyboard doesn't work at the Mint login screen.
I've tried passing various individual parameters to the kernel, via rEFInd based on recommendations for other hardware:
I noticed that grub seems to pass
$vt_handoff so I tried that as well.
All had no apparent effect on the keyboard; it still didn't work.
Of possible relevance, the kernel and initrd live on a ext4 partition, so rEFInd is using additional drivers to read them for EFI-stub booting. grub.efi is on my ESP (Fat32) and my firmware requires no additional drivers to read it.
What can I do to diagnose this problem? What might be the cause?