Subject: Re: [RFC] powerpc: Document new property called interrupt-parents

From: Segher Boessenkool <[email-masked]>
Date: Wed, 28 Feb 2007 19:54:31 +0100

>> Well, whatever Segher says, I'm still very concerned about the
>> potential for extra difficulty in debugging with this approach.
>
> The issue, as I understand it, is the potential for an old
> kernel parser to silently misparse a new dev tree with this
> new property.

Exactly.  Note that such such an old parser will misparse
the "interrupt-array" property as well, namely, not at all.
Debugging *could* be a bit easier though, who knows.

> Do the version and last_comp_version in the blob header
> help here?

That's not what those version fields are for.

The real solution is to just not use too old kernels with
too new a firmware/bootloader/device tree.  This issue
has existed for since forever and is in no way specific
to adding new OF bindings, or specific to Linux, or
anything like that.

> It's more of a general problem.

Quite so.

It might be worthwhile to add a device tree property
"minimum-linux-version" (in the tree root) that the kernel
will parse and complain about loudly if it doesn't match;
at a minimum it will make it super-duper clear to users
of a DTS with that property which combos work.  Documentation
rules ;-)

Segher