[Android Q&A, Help & Troubleshooting] social-design-concepts:
Accessing the Lenovo TAB S8-50 UEFI Setup

Accessing the Lenovo TAB S8-50 UEFI Setup :

You will need the following in order to access and navigate the uefi setup :

USB OTG Cable

Powered USB Hub

note : I tried 4 powered usb hubs and 2 usb-otg cables before finding a pair that work.

efibootmgr binary here : View attachment efibootmgr.zip

note : I did not port efibootmgr simply complied it from source found here.

Step 1. Extract the View attachment efibootmgr.zip somewhere on you computer and push efibootmgr32 to /data/local/tmp/

adb push efibootmgr32 /data/local/tmp/efibootmgr

Step 2. start an adb shell and navigate to /data/local/tmp

adb shell
shell@S8-50F:/ $ cd /data/local/tmp

Step 3. as root change permission of efibootmgr

shell@S8-50F:/data/local/tmp $ su
root@S8-50F:/data/local/tmp # chmod 6755 efibootmgr

Step 4. using efibootmgr

root@S8-50F:/data/local/tmp # ./efibootmgr -?
./efibootmgr: invalid option -- ?
efibootmgr version unknown (fix Makefile!)
usage: efibootmgr [options]
-a | --active sets bootnum active
-A | --inactive sets bootnum inactive
-b | --bootnum XXXX modify BootXXXX (hex)
-B | --delete-bootnum delete bootnum (hex)
-c | --create create new variable bootnum and add to bootorder
-D | --delete-by-label delete ALL boot entries with the same label
-d | --disk disk (defaults to /dev/sda) containing loader
-e | --edd [1|3|-1] force EDD 1.0 or 3.0 creation variables, or guess
-E | --device num EDD 1.0 device number (defaults to 0x80)
-g | --gpt force disk with invalid PMBR to be treated as GPT
-H | --acpi_hid XXXX set the ACPI HID (used with -i)
-i | --iface name create a netboot entry for the named interface
-l | --loader name (defaults to \elilo.efi)
-L | --label label Boot manager display label (defaults to "Linux")
-n | --bootnext XXXX set BootNext to XXXX (hex)
-N | --delete-bootnext delete BootNext
-o | --bootorder XXXX,YYYY,ZZZZ,... explicitly set BootOrder (hex)
-O | --delete-bootorder delete BootOrder
-p | --part part (defaults to 1) containing loader
-q | --quiet be quiet
| --test filename don't write to NVRAM, write to filename.
-t | --timeout seconds set boot manager timeout waiting for user input.
-T | --delete-timeout delete Timeout.
-u | --unicode | --UCS-2 pass extra args as UCS-2 (default is ASCII)
-U | --acpi_uid XXXX set the ACPI UID (used with -i)
-v | --verbose print additional information
-V | --version return version and exit
-w | --write-signature write unique sig to MBR if needed
-@ | --append-binary-args file append extra args from file (use "-" for stdin)

root@S8-50F:/data/local/tmp # ./efibootmgr -v
BootCurrent: 0000
Timeout: 10 seconds
BootOrder: 0000,0001
Boot0000* EFI Hard Drive ACPI(a0341d0,0)PCI(17,0)Controller(0)
Boot0001* EFI Internal Shell MM(b,fff68000,fff97fff)

Step 5. set next boot option / power off tablet

note : originally i used efibootmgr -n 0002 for setup but after accessing the setup menu this this boot option was no longer available ?

not sure what happened but maybe someone would be nice enough to post the output of efibootmgr -v for me.

root@S8-50F:/data/local/tmp # ./efibootmgr -n 0001
BootNext: 0001
BootCurrent: 0000
Timeout: 10 seconds
BootOrder: 0000,0001
Boot0000* EFI Hard Drive
Boot0001* EFI Internal Shell

root@S8-50F:/data/local/tmp # reboot -p

Step 6. Connect USB OTG cable , powered USB Hub, and keyboard to the tablet and power on.

Step 7. Exit the EFI Shell by typing exit then hit Enter

Step 8. Scroll down to Device Manager then hit Enter - Hit Enter again to select System Setup

Step 9. Scroll down to boot and hit Enter

Step 10. We need to disable UEFI Fastboot in order to be able to access the setup and boot manager directly from the keyboard.

Scroll down to fastboot and hit Enter arrow up and select disable and the press Enter the hit F4 to save changes.

Step 11. Hit Esc to return to the Main Setup Menu, Scroll down to Commit Changes the hit Enter, Hit Enter to confirm changes and the device will reboot.

You can now access the UEFI Setup by hitting F2 when powering the tablet on, or you can access the boot manger by pressing F7

In order to boot a traditional Linux distribution or Windows you need to change the OS Selection from Android to Windows 8.x tne the Boot Setup in the UEFI Setup menu.

These instructions are awful.