I was following this to secure-erase a used HDD. However, the computer was restarted before the erase completed. So, this is a case of known password. I thought that if I power cycled, and kept power on, the erase would finish. And it did, but the password was still active: Every boot requested this password during BIOS/UEFI startup.
Though it was not obvious because of how it was setup, it is possible to bypass this password. The result is that the drive is not accessible normally.
If the correct password is given during startup, the drive is accessible, but I was not able to disable security using hdparm on that power up. It seems like the key was to not give the password during startup and then use hdparm with the known correct password.
