quoted

AFAIK, its due the the inherent nature of tee_shm_alloc() and
tee_shm_register() where tee_shm_alloc() doesn't need to know whether
its a kernel or user-space memory since it is the one that allocates
whereas tee_shm_register() need to know that since it has to register
pre-allocated client memory.

quoted

- Why does tee_shm_register() unconditionally use non-contiguous
 allocations without ever taking into account whether or not
 OPTEE_SMC_SEC_CAP_DYNAMIC_SHM was set? It sounds like that's required
 from my reading of https://optee.readthedocs.io/en/latest/architecture/core.html#noncontiguous-shared-buffers.

Yeah, but do we have platforms in OP-TEE that don't support dynamic
shared memory? I guess it has become the sane default which is a
mandatory requirement when it comes to OP-TEE driver in u-boot.

quoted

- Why is TEE_SHM_REGISTER implemented at the TEE driver level when it is
 specific to OP-TEE? How to better abstract that away?

I would like you to go through Section "3.2.4. Shared Memory" in TEE
Client API Specification. There are two standard ways for shared
memory approach with TEE:

1. A Shared Memory block can either be existing Client Application
memory (kernel driver in our case) which is subsequently registered
with the TEE Client API (using tee_shm_register() in our case).

2. Or memory which is allocated on behalf of the Client Application
using the TEE
Client API (using tee_shm_alloc() in our case).

quoted

Let me know if you agree with the more minimal approach that I took for
these bug fix series or still feel like tee_shm_register() should be
fixed up so that it is usable. Thanks!

From drivers perspective I think the change should be:

tee_shm_alloc()

to

kcalloc()
tee_shm_register()

I've just posted "[PATCH 0/7] tee: shared memory updates",
https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@linaro.org/ (local)

Where tee_shm_alloc() is replaced by among other functions
tee_shm_alloc_kernel_buf(). tee_shm_alloc_kernel_buf() takes care of the
problem with TEE_SHM_DMA_BUF.

Thanks Jens. The series looks fine.  Tested too.

- Allen