linux-kernel - Re: [PATCH 9/9] x86: OLPC: add OLPC device-tree support

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Date:	Mon, 30 Aug 2010 14:49:46 -0400
From:	Andres Salomon <dilinger@...ued.net>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	devicetree-discuss@...ts.ozlabs.org, sparclinux@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, cjb@...top.org, Mitch Bradley <wmb@...top.org>,
	pgf@...top.org, linux-kernel@...r.kernel.org, davem@...emloft.net,
	Stephen Neuendorffer <stephen.neuendorffer@...inx.com>
Subject: Re: [PATCH 9/9] x86: OLPC: add OLPC device-tree support

On Mon, 30 Aug 2010 12:14:57 -0600
Grant Likely <grant.likely@...retlab.ca> wrote:

> On Sun, Aug 29, 2010 at 10:07 PM, Andres Salomon
> <dilinger@...ued.net> wrote:
> >
> > Make use of PROC_DEVICETREE to export the tree, and sparc's
> > PROMTREE code to call into OLPC's Open Firmware to build the tree.
> >
> > This also adds an init hook to proc_device_tree_init so that we can
> > ensure the device tree has been built prior to the proc_root_init
> > stuff attempting to populate /proc/device-tree.
> 
> I'm not clear as to why this is needed.  I would expect OLPC platform
> setup code would take care of extracting the device tree well before
> the kernel gets to setting up the representation in /proc/device-tree.
> 
> g.
> 

For simplicity; the OLPC platform setup code runs very early during
boot.  I preferred to keep that as minimal as possible, and defer
device tree allocation until the x86 mm code has finished initializing
(this skipping all the fun bootmem/etc work that'll be happening for
x86 soon).

Of course, once it's done initializing, one can either hardcode an
olpc_init_devtree call at the end of x86's setup_arch, or we can add a
generic hook for late devtree initialization right before proc
populates /proc/device-tree.  I chose the latter, but it could easily
be changed to the former if folks feel strongly about it.

I would've normally just used an initcall for it, but the proc_devtree
code runs prior to any of the initcall hooks.
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