Hi.

I was testing the SFN model on the TF-M 1.6 release and I am confused about which API source files should be used for the non-secure application.
The documentation here is lacking, so I am going by what we do in the build scripts of TF-M and tf-m-tests.
The non-secure source files that are exported and included in the nonsecure API library are tfm_<partition>_ipc_api.c.

This strikes me as odd, to use the IPC source files for the SFN model. If this is correct the naming is misleading.
From the code the selection is done based on PSA_API definition.
Based on this if this is the correct source files to use then I would think this should either be documented or renamed to something that better reflect the use, perhaps tfm_<partition>_psa_api.c?

In the documentation there is a lot of room for improvements, the existence of tfm_<partition>_secure_api.c could lead to confusion since it is not always well described.

tfm_attestation_integration_guide.rst:
System integrators might need to port these interfaces to a custom secure

partition manager implementation (SPM). Implementations in TF-M project can be

found here:

-  ``interface/src/tfm_initial_attestation_func_api.c``: non-secure interface

   implementation for library model

-  ``interface/src/tfm_initial_attestation_ipc_api.c``: non-secure interface

   implementation for IPC model

-  ``secure_fw/partitions/initial_attestation/tfm_attestation_secure_api.c``:

   secure interface implementation

Here it is not clear to me what “secure interface implementation” means, it could be interpreted as the SFN API.

tfm_crypto_integration_guide.rst:
- ``tfm_crypto_secure_api.c`` : This module implements the PSA Crypto API

  client interface exposed to the Secure Processing Environment

Here it is clearer that tfm_<partition>_secure_api.c is the interface to the SPE.
However the documented NSPE interface source file does not even exist, and does not explain the IPC / FUNC difference:
   | NSPE client API interface   | This module exports the client API of PSA Crypto to the NSPE  | ``./interface/src/tfm_crypto_api.c``

tfm_fwu_service.rst:
   | NSPE client API interface   | This module exports the client API of PSA Firmware Update to  | ``./interface/src/tfm_firmware_update_func_api.c``                                    |

   |                             | the NSPE(i.e. to the applications).                           | ``./interface/src/tfm_firmware_update_ipc_api.c``                                     |

Here it is mentioned the two possible source files, but it is not specified when to use which source file.

Generally:
Between all the services this is not consistently listed, for example the tfm_its_service.rst file does not have the table of source files.

If there is a general description of the non-secure interface sources, I couldn’t find it.

-Joakim AnderSSON