Subject: Request review of device tree documentation

From: [email-masked] (Benjamin Herrenschmidt)
Date: Mon, 14 Jun 2010 16:09:32 +1000

On Sun, 2010-06-13 at 23:13 -0600, Grant Likely wrote:
> > We use that to suck the device-tree, which we flatten, and then
> re-enter
> > the kernel with the "common" entry interface.
> 
> I don't think I want to do the same on ARM.  I'd rather have the
> prom_init stuff in a boot wrapper, or have OFW itself generate the
> flat representation before booting the kernel.

But then it's no longer OF. IE. A compliant OF implementation provides a
client interface API :-)

This is going to be especially important if Mitch wants to keep OF
alive.

I suppose it could be done via a wrapper like prom_init, which flattens
the tree, and sticks somewhere in a property the address of the OF
client interface callback though it's a tad awkward. If well defined, I
suppose Mitch might even be able to make his OF natively boot kernels
that way but that's of course up to him.

> I'm trying to constrain the number of things that could go wrong by
> defining only one way for getting the device tree data into the
> kernel.

I understand, and the flattened method is the most versatile, I'm just
pointing out the situation here :-)

> Right.  We don't need to use OFW/RTAS to handle this use case.

Definitely not. It will depend on whatever hypervisor interface is
implemented in a given environment. Though I do like the idea of passing
precompiled bits of .dtb around for hotplug :-) We could make that a
standard way of KVM to do things in embedded space.

Cheers,
Ben.