Hao Wu of Intel added Erase Block support to UFS (Universal Flash Storage) devices. Since UFS uses SCSI model in UEFI, the SCSI Unmap command was also added, but SCSI Unmap is not fully-implemented for SCSI devices, only for UFS Erase Block support.
[PATCH 0/2] Add Erase Block Protocol support for UFS devices
This patch series add the Erase Block Protocol implementation for UFS devices. Since the UFS transport layer follows the SCSI architecture, therefore, the implementation is added in the ScsiDiskDxe driver.
MdePkg IndustryStandard/Scsi.h: Add Unmap command support
MdeModulePkg ScsiDiskDxe: Add Erase Block Protocol support for UFS devices
For more information, see the patch on the EDK2-devel list, see the UFS 2.0 spec (including section 18.104.22.168). Hmm, unless I’m misreading things, the UFS spec is for members only, not public. 😦