[SLOF] [Qemu-ppc] [PATCH v4] board-qemu: add private hcall to inform host on "phandle" update

[Segher Boessenkool]

On Fri, Sep 29, 2017 at 08:08:56PM +0200, Thomas Huth wrote:
> On 29.09.2017 10:18, Segher Boessenkool wrote:
> > I'm a bit worried about the phandles FDT requires, which are a different
> > size than what OF uses (OF uses cell size, which is 64 bit on 64-bit OF;
> > the device tree specification uses 32 bit always).
> > 
> > Now usually everything lives low in memory, so the top 32 bits will all
> > be zeroes, but do we guarantee that anywhere (and do we want to restrict
> > to that!)
> 
> Currently QEMU puts the RTAS binary and the FDT just at the end of the
> RMA or below 2G, whatever is lower (look for RTAS_MAX_ADDR in
> hw/ppc/spapr.c). SLOF then puts itself right in front of the FDT from
> QEMU (see romfs_base in board-qemu/llfw/stage2.c in the SLOF sources),
> so everything related to SLOF always lives in the first 2G of RAM. Thus
> we should be fine here.

Yep, and SLOF encodes (at least some) ihandles as just 32 bit (and actually
reads them from the device tree again constantly, bad plan -- see other
thread).

I guess we can live with the restriction, certainly if we only do this
create-FDT-from-the-real-device-tree thing when running under QEMU.


Segher