Question about extension board used in U-boot

[François Ozog]

Hi Paul

Too posting because I think we also need to address this at a higher level.

i think we discussed this topic quite a while back. I may be wrong but it
may be Bill Mills who proposed to have an eeprom on the extensions that the
carrier board can use to detect and fetch proper overlay. Another way would
be that the contract between the extension board and the carrier board
includes an i2c accessible storage to fetch an overlay that would identify
the board and give all details. Bottom line, a software only solution seems
not entirely satisfying.
In that suboptimal case, U-Boot shall be able to assemble a DT for itself
and another for OS (may be same in some cases) through scripting. And in
this case, come your questions  below

.

Le sam. 18 sept. 2021 à 01:21, Ying-Chun Liu (PaulLiu) <paulliu at debian.org>
a écrit :

> 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
>
>
> --
François-Frédéric Ozog | *Director Business Development*
T: +33.67221.6485
francois.ozog at linaro.org | Skype: ffozog