Recommendation for identifying partition with firmware to be loaded from SD-card

[Daniel Thompson]

On Mon, May 01, 2023 at 04:26:25PM +0200, Heinrich Schuchardt wrote:
> <snip>
>
> Often firmware is separated into multiple parts due to firmware
> restrictions, e.g. U-Boot SPL and main U-Boot (e.g. as .itb file).
>
> Here the same considerations apply. Using a partition type GUID to
> identify further firmware parts to be loaded is best suited to
> avoid collisions.
>
> I would suggest to add a recommendation to the EBBR specification
> to use SoC specific partition type GUIDs to identify firmware to
> be loaded from SD-card.

EBBR currently recommends new devices load such firmware from the EFI
System Partition and provides guidance on using the directory structure
to avoid collisions:
https://arm-software.github.io/ebbr/index.html#firmware-partition-filesystem

This guidance describes "ideal" ROM-code and AFAIK is currently
aspirational since EBBR has not yet been around long enough to have
any impact on what SoC vendors ship in their ROM code.

Using ESP is optional and certainly there is no guidance in the spec
about selecting GUIDs to avoid collisions (e.g. don't use the same
GUID in next-gen chips that require different firmware).

IMHO guidance w.r.t. GUID colision avoidance is only useful if we
believe *future* SoC vendors will be unable to follow the current
prefer-to-use-ESP guidance (because anti-colision guidance will likely
take just as long to be implemented in SoC ROM code as
prefer-to-use-ESP guidance).


Daniel.