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.