Re: [Qemu-devel] [PATCH] hw/arm/virt: Add linux, pci-domain property

[Andrew Jones]

On Mon, Apr 23, 2018 at 02:11:40PM +0100, Peter Maydell wrote:
> On 23 April 2018 at 06:18, Jan Kiszka <address@hidden> wrote:
> > From: Jan Kiszka <address@hidden>
> >
> > This allows to pin the host controller in the Linux PCI domain space.
> > Linux requires that property to be available consistently or not at all,
> > in which case the domain number becomes unstable on additions/removals.
> > Adding it here won't make a difference in practice for most setups as we
> > only expose one controller.
> >
> > However, enabling Jailhouse on top may introduce another controller, and
> > that one would like to have stable address as well. So the property is
> > needed for the first controller as well.
> 
> Am I right in thinking that for ACPI the PCI domain number is
> communicated via the _SEG method? If so, looks like we already
> set that, and we set it to 0, which matches what we're doing here
> in the DT, so that's good.

_SEG and linux,pci-domain are similar in definition, but don't appear to
be equivalent, as the same _SEG number is permitted across multiple host
bridges, but linux,pci-domain must be unique for each host bridge. I
think the (_SEG, _BBN) pair may form the equivalent. We also set _BBN
to zero, so I think we're fine anyway.

> 
> > Signed-off-by: Jan Kiszka <address@hidden>
> > ---
> >  hw/arm/virt.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 94dcb125d3..943371b75e 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -1023,6 +1023,7 @@ static void create_pcie(const VirtMachineState *vms, 
> > qemu_irq *pic)
> >      qemu_fdt_setprop_string(vms->fdt, nodename, "device_type", "pci");
> >      qemu_fdt_setprop_cell(vms->fdt, nodename, "#address-cells", 3);
> >      qemu_fdt_setprop_cell(vms->fdt, nodename, "#size-cells", 2);
> > +    qemu_fdt_setprop_cell(vms->fdt, nodename, "linux,pci-domain", 0);
> >      qemu_fdt_setprop_cells(vms->fdt, nodename, "bus-range", 0,
> >                             nr_pcie_buses - 1);
> >      qemu_fdt_setprop(vms->fdt, nodename, "dma-coherent", NULL, 0);
> > --
> 
> Drew -- is minor changes to the DTC something we can do without
> having to condition it on machine version? I forget...

Yes, and even less minor changes than this one can be made to ACPI and DT
generation, per the "if a firwmare update could change it, then don't
worry about it" policy.

(I've CC'ed Igor in case he wants to chime in to correct anything I've
 said.)

Thanks,
drew