Question about extension board used in U-boot

[François Ozog]

Le sam. 18 sept. 2021 à 08:49, François Ozog <francois.ozog at linaro.org> a
écrit :

> 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.
>
i just forgot to state that the mode is well known: SPD for DIMMs.

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