[TF-A] Proposal: TF-A to adopt hand-off blocks (HOBs) for information passing between boot stages

[François Ozog]

Le ven. 9 juil. 2021 à 03:09, Julius Werner <jwerner at chromium.org> a écrit :

> > Of course every project would like not to change...
> >
> > For TF-A I wonder whether it will/should in fact use devicetree if there
> is a lot of complex data? TBD, I suppose.
>
> Okay, sorry, now I'm a bit confused -- I thought the discussion in
> this thread was about which parameter hand-off mechanism to use *for
> TF-A*? Or did it shift to discuss other projects in the meantime (I
> didn't always follow it closely)? I think it started with the UEFI
> guys wanting to implement a HOB format to interface with TF-A, and I
> think we now concluded that they're okay with using a simple parameter
> list instead (and wrapping their custom HOBs into a parameter blob
> that contains their UUID and everything else in the data part).
>
> So for TF-A, if the decision is that we want a parameter list, I think
> it makes sense to keep using the format that has already been there
> and in use for several years, and define new tags for the UEFI HOB use
> case in that. I don't really see a reason to switch TF-A and all other
> projects currently interfacing with it that way (e.g. coreboot) to
> something only used by U-Boot right now, if they're practically
> identical in concept.

Looking at bl_au_params: used by 3 SoCs to deal with gpio and serial.
Migration may not be that a big effort (handful lines of code?).
The key thing is that the biggest consumer of them are BL33 and a little
bit by some OS drivers (OS itself shall not be a consumer).
U-Boot has an established mechanism which is used in particular on all
chrome books in both x86 and Arm environments.
I have the impression that U-Boot is the typical BL33 so I would import the
mechanism into TFA, not the other way round.
EDK2 has typically its own code for TFA matters and may just import BL31,
so it does not appear a priority in that decision. But I may be wrong…

>
> --
François-Frédéric Ozog | *Director Business Development*
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