ACPI vs DT at runtime

Russell King - ARM Linux linux at
Mon Nov 18 10:19:01 EST 2013

On Mon, Nov 18, 2013 at 04:05:37PM +0100, Arnd Bergmann wrote:
> On Saturday 16 November 2013, Russell King - ARM Linux wrote:
> > On Fri, Nov 15, 2013 at 08:56:47PM +0100, Arnd Bergmann wrote:
> > > 
> > > For all I know, doing this in ACPI is something that is only now being
> > > discussed as Intel wants to be able to reuse the existing features from
> > > DT enabled drivers in the kernel and share the implementation between
> > > embedded x86 SoCs and embedded ARM/PowerPC/MIPS/... SoCs. That part actually
> > > isn't as crazy.
> > > 
> > > The existing ACPI usage however is basically all binary and cannot be
> > > shared with DT, in particular it won't help for the orthogonal problem of
> > > using ACPI to get "enterprise server" features on ARM64.
> > 
> > That's strange, because the patches I've seen from people who want to
> > add ACPI support to AMBA are all based around very similar strings to
> > those in DT to lookup the same data in ACPI.
> Can you point to specific patches?

No, because they weren't publically posted, so I don't feel that I can
say all that much; they were from quite a large company though.

> I can't say I'm an expert on this, but everything I've seen with ACPI
> is tables of binary data with four-letter identifiers that are defined
> by the ACPI group, but not using strings in a similar manner to DT.

They are using strings which are the same as the DT properties, but
without the vendor prefix - but yes, to only retrieve things like
booleans, u32s and such like.  They also have support for fixed-rate
clocks via the clk API too...

I'd like them to post the patches publically so a more open discussion
could occur.

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