linux-kernel - Re: [PATCH 03/11] x86/dtb: Add a device tree for CE4100

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Date:	Mon, 29 Nov 2010 13:07:20 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	<sodaville@...utronix.de>, <devicetree-discuss@...ts.ozlabs.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/11] x86/dtb: Add a device tree for CE4100

On Mon, 29 Nov 2010 09:53:29 +1100
Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> On Sun, 2010-11-28 at 17:04 +0100, Sebastian Andrzej Siewior wrote:
> > >> +	isa@...acy {

What is "@legacy"?  I don't think I've seen that in a unit address
before, googling only turns up this device tree, and a quick grep
through the ISA and base OF specs turns up nothing.

> > >> +		device_type = "isa";
> > >> +		compatible = "simple-bus";
> > >
> > >What does "simple-bus" means ?
> > I added simple bus in order to get probed. But I now I rember that this
> > is also supported per device_type. I get rid of it.
> 
> device_type is a nasty bugger, we are trying to get rid of Linux
> reliance on it.
> 
> Things like "simple-bus" don't rock my boat either, it's adding to the
> device-tree "informations" that are specific to the way Linux will
> interpret it, which is not how it should be.

The motivation for simple-bus comes from Linux, but its definition is
OS-neutral.  It indicates that no special bus knowledge is required to
access the devices under it.

I don't think it applies to ISA, though -- I/O space is special bus
knowledge, and the "ranges" looks weird for memory-space as well.

If we're going to get rid of device_type here, it would be nice to have
some other way to indicate that this node follows the ISA binding,
without having to recognize an implementation-specific compatible.

-Scott

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