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

[Laszlo Ersek]

On 06/10/15 21:34, 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. :)

On a second thought -- I *will* write the OVMF code for this now, or
tomorrow, because the syntax is *still* a little bit off. I think we'll
need:

  /address@hidden/address@hidden/address@hidden/address@hidden/address@hidden
                  ^^

The part I marked (ie. the @ and the UnitAddress after it) are
mandatory. I'll just hardcode the "@0" string there in QEMU, as written
above.

Thanks
Laszlo

> The SeaBIOS side I'll probably leave to you... /me ducks :)
> 
> Thanks
> Laszlo
>