Re: [Qemu-devel] [PATCH v2 4/4] hw/pci-bridge: push down PXB in qtree in order to format PXB bus numer

[Marcel Apfelbaum]

On 06/10/2015 10:34 PM, Laszlo Ersek wrote:
> On 06/10/15 21:26, Marcel Apfelbaum wrote:
> > On 06/10/2015 08:07 PM, Laszlo Ersek wrote:
> > > The PXB implementation doesn't allow firmware (SeaBIOS or OVMF) to boot
> > > off devices behind the PXB. This happens because the
> > > sysbus_get_fw_dev_path() function in "hw/core/sysbus.c" doesn't have
> > > enough information to format a unique identifier for the PXB in question,
> > > and consequently the OpenFirmware device path passed down to the guest
> > > firmware in the "bootorder" fw_cfg file is unusable for identifying the
> > > boot device.
> > >
> > > For example, the command line fragment
> > >
> > >     -device pxb,id=bridge1,bus_nr=4 \
> > >     \
> > >     -netdev user,id=netdev0 \
> > >     -device e1000,netdev=netdev0,bus=bridge1,addr=2,bootindex=0
> > >
> > > results in the following "bootorder" entry:
> > >
> > >     /pci/address@hidden/address@hidden/address@hidden
> > >
> > > The initial "pci" node is formatted by sysbus_get_fw_dev_path(), and the
> > > resultant OpenFirmware device path is independent of bus_nr=4 -- and
> > > therefore it is useless for identifying the device.
> > >
> > > In this patch we insert a dummy bus between the main sysbus and the
> > > TYPE_PXB_HOST device. Formatting child addresses is a bus class level
> > > responsibility, which is exactly what we'll use here.
> > >
> > > After the patch, the same command line fragment results in the following
> > > OpenFirmware device path in the "bootorder" fw_cfg file:
> > >
> > >     /extra-pci-roots/address@hidden/address@hidden/address@hidden/address@hidden
> > >
> > > The original, initial "/pci" fragment has been replaced with
> > > "/extra-pci-roots/address@hidden", which (a) looks better, (b) provides all
> > > the
> > > necessary information. sysbus_get_fw_dev_path() formats the first node
> > > ("extra-pci-roots") as always, and the new function
> > > extra_pci_roots_bus_get_fw_dev_path() formats the second one
> > > ("address@hidden").
> > >
> > > Here's the comparison ("diff -u -b -U28") between the "info qtree"
> > > outputs, before and after (the hpet device is the first common line):
> >
> > BTW, did you try to boot from it :) ?
>
> No, not yet; I'll have to write additional OVMF code for that; but the
> syntax is OK, and the information is there, so I'm fairly sure I can
> write that code. :)
>
> The SeaBIOS side I'll probably leave to you... /me ducks :)
I'll take it, sure, you are doing all the work anyway :)

Thanks,
Marcel
> Thanks
> Laszlo