[PATCH RFC 0/5] tee: optee: add RISC-V RPMI TEE transport

[Amirreza Zarrabi]

This RFC adds initial support for communicating with OP-TEE on RISC-V
using the RPMI TEE service group [1] over the SBI MPXY [2]
mailbox framework.

The intention is to provide a transport for RISC-V systems similar in
purpose to the FF-A transport currently used by OP-TEE on Arm systems.
Linux and OP-TEE act as endpoints of the RPMI TEE service group, while
the RPMI framework in machine-mode firmware mediates communication
between them.

The implementation closely follows the existing OP-TEE FF-A backend in
drivers/tee/optee/ffa_abi.c. Where possible, the same overall design and
lifetime rules are preserved, with FF-A operations mapped to equivalent
RPMI TEE services.

For shared memory, FF-A memory handles are replaced by RPMI memory parcel
identifiers. Linux creates an RPMI memory parcel for shared memory and
makes OP-TEE a receiver of that parcel. The parcel identifier is then
used in OP-TEE message parameters in a similar way to the FF-A global
memory handle.

RPMI TEE_CALL is used as the entry mechanism into OP-TEE, serving a role
similar to the FF-A direct-message path. The request and response contain
a small register-like payload carrying the OP-TEE call information and
state required to resume yielding calls. The existing OP-TEE call queue,
RPC handling and shared-memory infrastructure are reused as much as
possible.

The transport uses one SBI MPXY mailbox channel per hart. A TEE call is
issued using the channel corresponding to the CPU on which the call is
running. This preserves the execution model where entering OP-TEE on a
hart results in secure-world execution associated with that hart.

Shared memory is implemented using RPMI TEE memory parcels. The driver
maintains a mapping between parcel identifiers and struct tee_shm objects
and uses parcel create and reclaim operations to manage the lifetime of
memory shared with OP-TEE.

Asynchronous notifications are implemented using the RPMI TEE signal
bus. The RPMI TEE service group does not provide framework notification
events corresponding directly to the OP-TEE asynchronous notification
mechanism, so the signal bus is used to carry notification values from
OP-TEE to Linux.

This is an early RFC and the implementation is not complete. There may
still be functional bugs, incorrect assumptions, missing pieces, or
interfaces that need to change.

The series is being posted at this stage primarily to get feedback on the
overall architecture and on how the OP-TEE ABI is mapped onto the RPMI
TEE service group.

The implementation deliberately follows the FF-A backend and ffa_abi.c
closely. This allows the existing OP-TEE driver design to be reused and
keeps the RISC-V and FF-A transports as consistent as possible. Some of
these abstractions may need to be adjusted where the RPMI execution,
notification, or memory model differs from FF-A, while others may
eventually be shared between the transports.

[1] https://github.com/riscv-non-isa/riscv-rpmi/commits/main/src/srvgrp-tee.adoc
[2] https://github.com/riscv-non-isa/riscv-sbi-doc/releases

Signed-off-by: Amirreza Zarrabi <amirreza.zarrabi@xxxxxxxxxxxxxxxx>
---
Amirreza Zarrabi (5):
      optee: riscv: add RPMI TEE service group transport
      optee: riscv: add shared memory and scheduled calls
      optee: riscv: enable persistent shared argument cache
      optee: riscv: add asynchronous notifications over the signal bus
      dt-bindings: tee: add RISC-V RPMI TEE transport

 .../bindings/tee/riscv,rpmi-mpxy-tee.yaml          |   65 +
 MAINTAINERS                                        |    1 +
 drivers/tee/optee/Makefile                         |    1 +
 drivers/tee/optee/core.c                           |    8 +-
 drivers/tee/optee/optee_private.h                  |   47 +
 drivers/tee/optee/optee_riscv.c                    | 1621 ++++++++++++++++++++
 drivers/tee/optee/optee_riscv.h                    |  334 ++++
 include/linux/mailbox/riscv-rpmi-message.h         |    1 +
 8 files changed, 2076 insertions(+), 2 deletions(-)
---
base-commit: 68142f986ff04b2b70b31db00f719bf690f64a9a
change-id: 20260912-rpmi-tee-service-grp-dev-b2ce2f63e0df

Best regards,
-- 
Amirreza Zarrabi <amirreza.zarrabi@xxxxxxxxxxxxxxxx>