[libvirt] [PATCH 0/3] add pci-bridge device and address type

[Osier Yang]

On 2012年12月26日 16:28, Osier Yang wrote:
> On 2012年12月26日 16:12, li guang wrote:
>> 在 2012-12-26三的 15:38 +0800，Osier Yang写道：
>>> On 2012年12月26日 09:00, liguang wrote:
>>>> Now, it's unnecessary to arrange devices into multi-pci-bus,
>>>> for example:
>>>> <sound model='ac97'>
>>>> <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
>>>> function='0x0'/>
>>>> </sound>
>>>> <video>
>>>> <model type='cirrus' vram='9216' heads='1'/>
>>>> <address type='pci' domain='0x0000' bus='0x1' slot='0x02'
>>>> function='0x0'/>
>>>> </video>
>>>> libvirt will complain about "bus != 0",
>>>> fortunately, qemu supports pci-to-pci bridge,
>>>> if we want to use multi-pci-bus, we can define
>>>> 2 pci bridge devices then attach 1 to the other
>>>> as a subordinate pci-bus, so, 2 pci-buses appear.
>>>> for example:
>>>> <pci-bridge type='root'/>
>>>> <pci-bridge type='subordinate'>
>>>> <address type='pci-bridge' domain='0x0000' bus='0x00' slot='0x04'
>>>> function='0x0'/>
>>>> </pci-bridge>
>>>> <sound model='ac97'>
>>>> <address type='pci-bridge' domain='0x0000' bus='0x01' slot='0x02'
>>>> function='0x0'/>
>>>> </sound>
>>>> <video>
>>>> <model type='cirrus' vram='9216' heads='1'/>
>>>> <address type='pci-bridge' domain='0x0000' bus='0x00' slot='0x02'
>>>> function='0x0'/>
>>>> </video>
>>>
>>> I think this is rather not workable, E.g. how to known the video device
>>> attached to which pci bridge if there are multiple pci bridges?
>>
>> please bear in mind bus 0 is root bridge, bus 1 is subordinate bridge,
>> and so forth, which was implemented in my patch 2/3
>
> That doesn't answer the question.
>
>>
>>> And the
>>> new address type "pci-bridge" looks bogus, as the address properties of
>>> a pci bridge are exactly same with a normal pci device.
>>>
>>> From the qemu patch:
>>>
>>> -device pci-bridge,id=bridge1 \
>>> -netdev user,id=u \
>>> -device ne2k_pci,id=net2,bus=bridge1,netdev=u
>>>
>>> I think what we only need is to describe the relapship between pci
>>> bridge and pci bridge (if it's supported, the two types "root" and
>>> "subordinate" are not enough to describe the relatioship), also pci
>>> device and pci bridge.
>>
>> relationship between pci-bus and devices are embedded, just like
>> pci.0, e.g.
>> <address type='pci' domain='0x0000' bus='0x00' slot='0x04'
>> function='0x0'/>
>> means a device sitting on bus pci.0 slot 4
>> then after my changes
>> <address type='pci-bridge' domain='0x0000' bus='0x00' slot='0x04'
>> function='0x0'/>
>> would have the same mean
>> relationship between pci-bridges are primary and secondary,
>> (as far as I know qemu doesn’t support multi-pci-bridges at present)
>> so root and subordinate attribute may be enough,

By the way, what I get from Michael S. Tsirkin is: More than
2 bridges *should* work.

>
> No, even it's not supported now, the proposed XML should be
> designed compatible enough for future. Note that as long
> as a new XML is added, it can't changed/removed for back-compact,
> so when introducing new XMLs, you should consider the future.
>
> And on other hand, the introduced XML should be general
> enough for all drivers, not only QEMU.
>
> Anyway, regardless of the current qemu implementation, I think
> you should refer to the specification of PCI SGI, so that the
> proposed XML could be compatible enough for the future.
>
>> every subordinate will attach to root bridge, and has its own slot.
>>
>>>
>>> To describe the relationship between bridges, perhaps we will need
>>> "parent" and "child" properties for<pcibridge> device.
>>>
>>> To describe the relatioship between a pci device and a pci bridge,
>>> a property like "bridge" for general pci device should be enough.
>>> In this case, another property for<pcibridge> is needed, to
>>> indentify it, such as "id" or "name".
>>
>> only relationship is not enough, it's unsuitable for passing '-device
>> pci-bridge' to qemu, so I define a new device and address type for
>> pci-bridge in libvirt.
>>
>>>
>>> Regards,
>>> Osier
>>>
>>>
>>
>
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