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

[Scott Wood <scottwood@freescale.com>]

On 07/23/2013 04:15:59 PM, Alexander Graf wrote:
> 
> 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.

So why do we need the dry run stuff?

-SCott