On Fri, 27 Feb 2026, Aditya Gupta wrote:
On 26/02/27 02:05PM, BALATON Zoltan wrote:
On Fri, 27 Feb 2026, Aditya Gupta wrote:
On 26/02/27 03:43PM, shivang upadhyay wrote:
<...snip...>
Q: can the generated DBT genuinely be different on a
subsequent reset than it was when QEMU first starts?
The comments in the pnv_reset() code seem to suggest it,
but on the other hand the code as written will only
call pnv_dt_create() and update machine->fdt once on first
reset, not on later resets. So perhaps the comment is
just confusingly worded ?
Yes, I am not much familiar with the design here. But, as per
my current understanding of this code, DTB content should not
not be changed.
To add to this, yes, normally reset path doesn't change the device tree,
since all reboots are the same as the first boot.
As of upstream this is true, I don't see dtb changing between resets.
Isn't VOF allowing clients to do setprop that would be changing the device
tree? Some settings are stored there so maybe it can be changed by the guest
that should be preserved between reboots?
By VOF did you mean the pseries f/w ?
I don't know much about these machines. I meant Virtual Open Firmware in
QEMU or SLOF which it can replace. But maybe this is only used by spapr so
does not affect pseries but in spapr there's spapr_vof_setprop() which
looks like it can change the fdt. Maybe it's handled differently on
pseries, I don't know.
i don't see anything changing the dt in powernv as of now, but
for some edge case, where that is possible (will be possible atleast
after mpipl support is merged), we can always update the fdt in below 2
if cases in pnv_reset:
> if (machine->fdt) {
> fdt = machine->fdt;
> } else {
> fdt = pnv_dt_create(machine);
> /* Pack resulting tree */
> _FDT((fdt_pack(fdt)));
> }
machine->fdt will never be NULL since it's being set in pnv_init
should we just do pnv_dt_create on every pnv_reset ?
I don't know either but wasn't original code meant to either create an fdt
or take what the user specified with -dtb option or similiar? In that case
maybe you don't want to override the user specified dtb but I could be
wrong about what this is meant to do as I have no idea whatsoever about
these machines.
Regards,
BALATON Zoltan
