ufs: rpmb: make RPMB usable with OP-TEE key derivation

[Jorge Ramirez-Ortiz <jorge.ramirez@oss.qualcomm.com>]

This series makes UFS RPMB work out of the box with an OP-TEE that
implements the standard eMMC RPMB key-derivation flow, without requiring
any fundamental changes on the OP-TEE side.

RPMB provides an authenticated, replay-protected storage area whose
security relies on a secret authentication key. In our setup that key is
never exposed to the kernel: OP-TEE derives it in the secure world from
its hardware-unique key and a device identifier (dev_id) that the RPMB
core hands down. OP-TEE's implementation targets eMMC, where dev_id is
the 16-byte eMMC CID, and both the fixed length and the raw-CID layout
are baked into its key derivation.

Two things stand in the way of reusing that same, unmodified OP-TEE flow
for UFS RPMB:

  1. On a cold boot the very first frame sent to the RPMB well-known LU
     comes back with a power-on UNIT ATTENTION (ASC 0x29), which the SCSI
     core reports rather than retries. RPMB has no earlier guaranteed
     access that could clear the condition first, so RPMB fails on every
     power cycle. Patch 1 asks the SCSI core to retry the power-on UNIT
     ATTENTION on the RPMB WLUN.

  2. The UFS RPMB id is "<device_id>-R<region>", which is variable length
     and longer than 16 bytes. Passing it verbatim would tie the derived
     key to a length OP-TEE does not expect and diverge from the fixed
     eMMC CID ABI. Patch 2 hashes it into a fixed 16-byte dev_id with
     blake2s, keeping the key stable and unique per region while matching
     the eMMC CID layout OP-TEE relies on. The hash algorithm and input
     string are thus part of the key-derivation ABI and must stay stable.

With both patches, UFS RPMB is functional from the first access after a
cold boot and derives keys through the existing eMMC-style OP-TEE flow,
(requires minimal OP-TEE changes).

Jorge Ramirez-Ortiz (2):
  ufs: rpmb: retry power-on UNIT ATTENTION on the RPMB WLUN
  ufs: rpmb: use a fixed-length RPMB dev_id

 drivers/ufs/Kconfig         |  1 +
 drivers/ufs/core/ufs-rpmb.c | 41 ++++++++++++++++++++++++++++++++++---
 2 files changed, 39 insertions(+), 3 deletions(-)