We need a uniform mechanism for hardware discovery.There is no hardware platform available at this point. From a kernel perspective, the aim is to minimise (or even completely remove) the platform code from the architecture specific directory. FDT is currently mandated and there are ongoing discussions for ACPI support.
Currently this is a mess on tablets and smartphones with arm as far as I know.
Having ACPI would make everything a lot easier for software development and shorten the time for hardware integrators and platform makers to release new designs.
We want ACPI, we want ACPI!
Having ACPI on mobile phones and tablets would be awesome from a hardware point of view.
Plus it makes things easier to do, much easier to do.
(Heard that Microsoft is already asking ACPI for things that run windows 8.)
Seems like it's best to add ACPI anyway.