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Re: [Qemu-devel] [PATCH] PPC: E500: Generate device tree on reset

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH] PPC: E500: Generate device tree on reset
Date: Tue, 23 Jul 2013 23:15:59 +0200

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.
> If you can't produce the entire device tree at init time, how can you 
> calculate its size with a dry run?
> 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.


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