For a long time, I believed it was impossible to lock and unlock the xbox hdd with a USB-(S)ATA adapter. But apparently somebody has done it with
JMicron chipset and it is also supported in
Cypress chipset.
p-eak's comment on honzaf's patch to hdparm revealed he did a security erase which is indicative of use of the ATA security features. I did some work on incorporating hdparm stuff into
hdtool - I am hoping I can recall enough of that stuff and use honzaf's patch in hdtool.
This requires further investigation. It will open up another avenue of doing hdd upgrades if successful as hdtool is the key component in xboxhdm2.X hdd lock/unlocking.