Hi all,

 

I am trying to align TrustZone initialisation procedure between TF-M and CMSIS.

 

In CMSIS the approach from the early v8-M days is to have a “partition.h” file providing “TZ_SAU_Setup()” function. This function is called during low level “SystemInit()” which runs as part of the pre-main (called from ResetHandler and before running C lib init).

 

In contrast TF-M calls “tfm_spm_hal_init_isolation_hw()” (which is similar to “TZ_SAU_Setup()” plus PPC/MPC configuration) during “tfm_core_init()” (which runs in secure “main()”).

 

The advantage of “TZ_SAU_Setup()” is that this function is available by standard for all TrustZone devices. The shortcoming is it doesn’t cover MPC/PPC configuration, yet. Ideally we can enhance CMSIS standard to offer a “TrustZone_Setup()” function (the name is still to be defined) that does all this. That would simplify the TF-M HAL to just one single function call that should be provided by each TrustZone-Device low level init code.

 

The final question is: When does this function need to be called? Are you aware of any reason why we should not configure the “system isolation” already during low level init (pre-main)? This could simplify TF-M code even more. In TF-M we could simply rely on a properly configured TrustZone isolation before running any TF-M code.

 

Cheers,

 

Jonatan Antoni

Senior Engineering Manager - CMSIS

 

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