ACPI vs DT at runtime

[Stefano Stabellini]

On Tue, 19 Nov 2013, Mark Rutland wrote:
> > We all know DT considerably better to a point where I would recommend
> > that they flash a DTB in their UEFI firmware instead of go with ACPI. For
> > simple hardware and basic devices we've got most bindings sorted out by
> > now, and we've decided on backwards compatibility from here on out.
> 
> If a vendor does this, with a DTB that correctly describes their
> hardware then I am not against it (and would prefer this case to mapping
> from ACPI to DT).

I think that the firmware passing a DTB to the bootloader/kernel is the
best option we have.


> For that case we will also require a nailed-down boot
> protocol that allows for either DTB or ACPI.

The latest documentation patch for the "arm/arm64 UEFI boot protocol"
implies that UEFI on ARM is already capable of passing a DTB to the
kernel:

"The implementation depends on receiving information about the UEFI
environment in a Flattened Device Tree (FDT) - so is only available with
CONFIG_OF."

Maybe we just need to better document it?


> (only one at a time)

I would not go as far as requiring that only one is available.
Certainly I would mandate that either of them are independently complete
and sufficient to describe the platform.