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

[Laszlo Ersek <lersek@redhat.com>]

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/pci-bridge@0/ethernet@2/ethernet-phy@0
>>
>> 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/pxbhost@4/pci-bridge@0/ethernet@2/ethernet-phy@0
>>
>> The original, initial "/pci" fragment has been replaced with
>> "/extra-pci-roots/pxbhost@4", 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
>> ("pxbhost@4").
>>
>> 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 :)

Thanks
Laszlo