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

[Daniel Thompson]

On Fri, Jul 09, 2021 at 09:05:09AM +0200, François Ozog wrote:
> 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.

I presume this analysis only covers those SoCs where someone (vendor,
customer, community) has upstreamed their TF-A implementation?

It is only relatively recently[1] that the TF-A CLA requirements that
inhibited upstreaming were relaxed. Additionally the current silicon
supply crunch is forcing board designers to second (third and forth)
source critical components which can drive usage of firmware parameter
passing.

In short are you confident adopting a mantra of "it doesn't exist
unless it's upstreamed" is sufficient?


Daniel.


[1] Perhaps not that recent if measured in years... but certainly
    recent relative to firmware life cycles!


> 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* T:
> +33.67221.6485 francois.ozog at linaro.org | Skype: ffozog
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