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

[Scott Wood <scottwood@freescale.com>]

On 07/23/2013 04:44:02 PM, Alexander Graf wrote:
> 
> 
> Am 23.07.2013 um 23:19 schrieb 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?
> 
> Because dumpdtb otherwise generates a halfway complete dtb on the  
> first dry pass as device realization is yet incomplete :).

What I mean is why have a first pass at all?

-Scott