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Date: Tue, 23 Jul 2013 16:19:04 -0500
From: Scott Wood <scottwood@freescale.com>
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Subject: Re: [Qemu-devel] [PATCH] PPC: E500: Generate device tree on reset
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To: Alexander Graf <agraf@suse.de>
Cc: "qemu-ppc@nongnu.org list:PowerPC" <qemu-ppc@nongnu.org>, qemu-devel Developers <qemu-devel@nongnu.org>

On 07/23/2013 04:15:59 PM, Alexander Graf wrote:
>=20
> On 23.07.2013, at 21:38, Scott Wood wrote:
>=20
> > On 07/22/2013 10:28:17 AM, Alexander Graf wrote:
> >> Today we generate the device tree once on machine initialization =20
> and then
> >> store the finalized blob in memory to reload it on reset.
> >> This is bad for 2 reasons. First we potentially waste a bunch of =20
> RAM for no
> >> good reason, as we have all information required to regenerate the =20
> device
> >> tree available anyways.
> >> The second reason is even more important. On machine init when we =20
> generate
> >> the device tree for the first time, we don't have all of the =20
> devices fully
> >> initialized yet. But the device tree needs to potentially walk =20
> devices to
> >> put information about them into the device tree.
> >
> > If you can't produce the entire device tree at init time, how can =20
> you calculate its size with a dry run?
> >
> > Device trees are generally pretty small; couldn't we just set a =20
> maximum size and allocate that much space?
>=20
> It's what we do, unless we load it from the disk. In that case we =20
> take the fdt size from disk.

So why do we need the dry run stuff?

-SCott=