Hi Jun Chen

I think this TBBR FWU documentation https://trustedfirmware-a.readthedocs.io/en/latest/components/firmware-update.html?highlight=FWU#tbbr-firmware-update-tbbr-fwu might help you understand the role of BL2U in FWU.
Secure-world BL2U is mainly responsible for platform setup, for example initializing TZC [1] and Non-Secure BL2U writes new images to non-volatile memory such as NAND flash. Is this helpful? If you have any further questions, please do not hesitate to contact us.

[1]: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/bl2u/bl2u_main.c

Thanks,

Manish Badarkhe

From: Jun.Chen(陳奕?) via TF-A <tf-a@lists.trustedfirmware.org>
Date: Thursday, 16 February 2023 at 11:32
To: tf-a@lists.trustedfirmware.org <tf-a@lists.trustedfirmware.org>
Subject: [TF-A] Is NS_BL1U necessary to do FWU ?

Hi,

In ARM TBBR, there is a requirement

“R0100_TBBR_AFM_FLASHING” (The AP firmware must switch to the Non-Trusted world for executing the SoC firmware loader),

But there is no requirement for secure boot as long as I finish chain if ROT verification.

So, can I implement FWU in BL2 which is verified and load from BL1 (ROM)?

For example,

   BL1(ROM) -> Load and verify BL2U with new image from SD to secure RAM -> execute BL2U in Secure RAM then write new image to NAND flash

Best regards,

Jun