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From: Alexander Graf <agraf@suse.de>
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Date: Tue, 23 Jul 2013 23:15:59 +0200
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Subject: Re: [Qemu-devel] [PATCH] PPC: E500: Generate device tree on reset
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To: Scott Wood <scottwood@freescale.com>
Cc: "qemu-ppc@nongnu.org list:PowerPC" <qemu-ppc@nongnu.org>, qemu-devel Developers <qemu-devel@nongnu.org>


On 23.07.2013, at 21:38, Scott Wood wrote:

> On 07/22/2013 10:28:17 AM, Alexander Graf wrote:
>> Today we generate the device tree once on machine initialization 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 RAM =
for no
>> good reason, as we have all information required to regenerate the =
device
>> tree available anyways.
>> The second reason is even more important. On machine init when we =
generate
>> the device tree for the first time, we don't have all of the devices =
fully
>> initialized yet. But the device tree needs to potentially walk =
devices to
>> put information about them into the device tree.
>=20
> If you can't produce the entire device tree at init time, how can you =
calculate its size with a dry run?
>=20
> Device trees are generally pretty small; couldn't we just set a =
maximum size and allocate that much space?

It's what we do, unless we load it from the disk. In that case we take =
the fdt size from disk.


Alex