Question about extension board used in U-boot

["Ying-Chun Liu (PaulLiu)" <paulliu@debian.org>]

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Hi all,


I have some questions about how to implement extension board usage.
My case is on imx8mm-cl-iot-gate. It can add three different types of
extension boards.
One of the extension boards is SPI extension which have 3 empty slots.
And you can add
some small boards onto it. One of them is a "TPM2" module.


My first question is if I want to use tpm2 in U-boot for measured boot.
How to implement this right? Currently I just modify the dts used by
U-boot to let it drive
the extension board. And let it drive the TPM. But it is not good for
upstreaming because
when other types of extension boards installed then it is not working.
Where to implement this? What is the best practice of this?


The second question is about extension manager.
I have read the extension.rst. I think I'll implement this anyway
because then
I can have a command to query what type of extension boards I have.
And if the extension board is the 3 slots one. I can then detect which
slot is the TPM.
I'll implement this anyway because the "extension" command is convenient
for users.
But it seems to me that it only solves the problem for Linux kernel.
It can apply a DTB Overlay to Linux DTB to let Linux knows we have that
extension board.
But it is too late for U-boot itself, right?


The third question is I'm also dong SystemReady IR certificate. That means
the dtb for Linux is directly provided by U-boot. We use U-boot dtb
directly to Linux
kernel. In this case, how to modify that dts dynamically to feed to the
Linux kernel by
the extension manager?
What is the best practice if I want to use U-boot dts for Linux in
implementation?


Thanks a lot.


Yours,
Paul



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