Add custom entry to /etc/grub.d/40_custom file:
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
menuentry "Bios upgrade" {
insmod part_gpt
insmod ext2
set root=(hd0,gpt2)
linux16 /boot/memdisk iso
initrd16 /boot/biosupgrade.iso
}
for gpt partition table root disk and root partition is second.
/boot/memdisk is copy of /usr/share/syslinux/memdisk part of syslinux package.
Then create new boot record:
$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg
Reboot now and choose new grub2 entry Bios upgrade.
