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

[Simon Glass]

Hi Julius,

On Thu, 8 Jul 2021 at 15:56, Julius Werner <jwerner at chromium.org> wrote:

> Thank you all for your feedback.
>>
>> It appears that in theory we are all happy with using bloblist with few
>> implementation details which needs to be taken care of during
>> implementation.
>>
>
> Just to clarify: are you using "bloblist" as a general term for the
> concept of a simple linked list of tagged data blobs, or to refer
> specifically to the U-Boot implementation with that name? The existing TF-A
> implementation (bl_aux_params) is basically identical in concept to the
> U-Boot bloblist, but not binary compatible. Are we talking about just
> keeping that, or throwing it away in order to reimplement the exact
> structure U-Boot is using? (I would prefer to keep the bl_aux_params as
> they are to avoid disrupting existing uses, of course. Making
> backwards-incompatible changes to an interface that passes across multiple
> repos and firmware components is always a big pain.)
>

My understanding is that it is U-Boot's bloblist, since it is the lynchpin
here, but perhaps with some changes to support features it may lack. It has
been in U-Boot for a couple of years and is supported in TPL, SPL and
U-Boot proper. It has a good set of unit tests and should be easy enough to
lift into other projects. Note that it is not really a linked list, though
that is one of the extensions proposed.

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.

Regards,
Simon