Re: [PATCH v3] misc: Add RZG2L OTP support

[Mathieu Othacehe <othacehe@gnu.org>]

Hello,

> Is there any reason for not using SMCC to access OTP region?
>
> Currently we use SMCC for reading various bits in OTP region.
> We could add SMCC handler in TF-A for fuse programming
> rather than exposing OTP region to normal world

My original reasoning was that the only existing way to do the fusing
was to go through the OP-TEE fork of Renesas. As, I do not want to use
OP-TEE (even more a fork) on my project, it was not suiting my needs.

Now Marek also raised this point, but I wasn't aware of this SMCC
interface between U-Boot and the TF-A. On the TF-A side, I can find this
handler[1], but nothing on the U-Boot side, even on Renesas fork. Am I
missing something?

If there's already a communication channel that can be used, then we
would need to add fusing support to the TF-A, and turn my driver into
something way more minimal that would just perform SMCC calls to the
TF-A. That would feel like a better option overall, as it would not
require a TF-A modification to allow fusing in the non-secure world in
the first place.

Thanks,

Mathieu
[1]: https://github.com/renesas-rz/rzg_trusted-firmware-a/blob/v2.5/rzg2l/plat/renesas/rz/common/rz_plat_sip_handler.c