[PATCH] imx: hab: Make imx_hab_is_enabled dependent on FIELD_RETURN

[Paul Geurts]

>> The decision on whether HAB is enabled is solely based on the SEC_CONFIG
>> fuse. The HAB FIELD_RETURN feature is able to permanently disable HAB on
>> a CPU, after which it is able to boot unsigned firmware. U-Boot however
>> does not take into account the FIELD_RETURN mode, and refuses to boot
>> unsigned software when the feature is enabled.
>> 
>> Also take the FIELD_RETURN fuse into account when deciding whether HAB
>> is enabled. When The FIELD_RETURN fuse is blown, HAB is not enabled.
>> 
>> Tested on i.MX8M Mini, i.MX8M Plus, i.MX8M Nano and i.MX6ULL
>
>The purpose of the field return fuse is to unlock a system when it is 
>returned to factory, right ?

That is the intention of the field return mode indeed.

>
>Can the system be re-locked afterward too ?

No, the field return is enabled by a fuse, which cannot be reverted. The
mode is intended to be able to perform investigations on broken devices,
but these devices are not intended to go back into the field.