On 9/18/21 8:54 AM, François Ozog wrote:

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

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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.

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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@debian.org a écrit :

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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.

You could implement the weak function board_fdt_blob_setup() to detect your addon boards and extend the devicetree.

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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

Measured boot is provided in U-Boot v2021.10-rc4 based on TPMv2. Just enable CONFIG_EFI_TCG2_PROTOCOL.

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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?

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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?

U-Boot has a fdt command which you could use to apply overlays. Or implement function board_fdt_blob_setup().

Best regards

Heinrich

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

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François-Frédéric Ozog | *Director Business Development* T: +33.67221.6485 francois.ozog@linaro.org | Skype: ffozog _______________________________________________ boot-architecture mailing list boot-architecture@lists.linaro.org https://lists.linaro.org/mailman/listinfo/boot-architecture

Le lun. 20 sept. 2021 à 13:32, Daniel Thompson daniel.thompson@linaro.org a écrit :

On Sat, Sep 18, 2021 at 08:49:48AM +0200, François Ozog wrote:

...

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.

What you're describing sounds exactly like Raspberry Pi HATs work: https://github.com/raspberrypi/hats/blob/master/devicetree-guide.md

Similarly Beagleboard capes use rely on I2C EEPROMs for make them discoverable, although I don't think all have to have a built-in overlay (IIRC because they joined the party too early).

I believe this would be a great SystemReady addition: define details of the DT lifecycle and probably adopt one of the two models. Or worst case define a consolidated one. I hope this is also adoptable by 96boards…

In other words there's plenty of prior art here and, as new hardware standards come out, it should be much easier for them to find this prior art. However I'm near certain mistakes will still be made...

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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.

Sub-optimal or not[1] the u-boot extension board code still looks like it would be a good starting point even for boards with non-discoverable extensions (96Boards CE 1.0 for example).

If implementing on a board with non-discoverable extensions then I would consider implementing "extension scan" to report non-discoverable modules (e.g. from an internal list) and proposing patches to that "extension apply all" would not enable non-discoverable boards (so that non- discoverable boards would have to be enabled by injecting a "extension apply <id>" into the boot scripts).

Of course, I may have overlooked a better existing mechanism in u-boot but that's what I would start with until I was corrected by maintainers ;-) .

Daniel.

[1] And also extremely off-topic for Paul since his (a) boards are discoverable and (b) the extension framework can't fire up early enough for TPM extensions ;-) .

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Le sam. 18 sept. 2021 à 01:21, Ying-Chun Liu (PaulLiu) <

paulliu@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@linaro.org | Skype: ffozog _______________________________________________ boot-architecture mailing list boot-architecture@lists.linaro.org https://lists.linaro.org/mailman/listinfo/boot-architecture