On Fri, Oct 24, 2014 at 02:38:39PM +0200, David Gibson wrote: > On Thu, Oct 23, 2014 at 01:26:08PM +0200, Alexander Graf wrote: > > > > > > On 23.10.14 13:24, Peter Maydell wrote: > > > On 23 October 2014 12:23, Alexander Graf <ag...@suse.de> wrote: > > >> On 23.10.14 12:19, Ard Biesheuvel wrote: > > >>> The reason for this change was that, before, the DTB would only be > > >>> generated once, and after a reset, the machine would go through the > > >>> kernel boot protocol as before but the DTB pointer would point to > > >>> garbage. Any idea how ppc deals with this? Do they recreate the device > > >>> tree after each reset? > > >> > > >> Yes, we regenerate the device tree on each reset. > > > > > > Any particular reason? Surely it's always the same... > > > > We have the code in place anyway, it's not a performance critical code > > path and putting it into a rom would be a waste of RAM, as it'd keep yet > > another copy of something we can easily regenerate. > > > > It's a matter of personal preference I guess. > > The "pseries" machine actually uses an odd hybrid. We create a > "template" device tree with the common portions during early init. > That's stored permanently, but is not guest visible. > > At reset time we augment the template with information which could > very from one boot to another, then copy it into RAM for the SLOF > firmware to read. > > It's not particularly efficient, but really, who cares. It's once per > resent, and we're generally talking at most a few dozen kiB of device > tree.
Oh, also, because we potentially have hotplug of VIO devices, it's
*not* necessarily the same every time.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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