I ran into this problem as well with my Dell Latitude e7440 and Slackware64 14.1.
In pure UEFI mode, with a hybrid (GPT/MBR) bootable USB thumb drive, I am able to get as far as selecting the keymap. I cannot select a keymap with the built-in keyboard.
, I see the keyboard as:
input: AT Raw Set 2 keyboard as /devices/platform/i8042/serio0/input/input1
Work-around #1: By plugging in an external USB keyboard, I am able to proceed normally. Once the install is complete, and I reboot, the built-in keyboard works as expected.
Work-around #2: I enabled CSM (legacy ROM support) in the BIOS setup. Then, I wrote the Slackware64 14.1 disc image to an MBR-only USB thumb drive. The built-in keyboard works fine.
With a properly working built-in keyboard, dmesg
input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input1
The caveat to work-around #2 is that the Slackware install will not detect a UEFI system, so it won't offer to install eLILO for you.
To get around this, I allowed the installer to create a bootable thumb drive to boot into the new install. Then, I was able to manually install eLILO. I rebooted into BIOS setup, disabled CSM, and was finally able to boot into pure UEFI Slack64.