Re: [Qemu-devel] [PATCH RFC 1/1] s390x/pci: Extend pci representation by new zpci device

[Alexander Graf]

On 26.02.15 16:27, Frank Blaschka wrote:
> On Thu, Feb 26, 2015 at 03:39:15PM +0100, Alexander Graf wrote:
>>
>>
>> On 26.02.15 12:59, Frank Blaschka wrote:
>>> This patch extends the current s390 pci implementation to
>>> provide more flexibility in configuration of s390 specific
>>> device handling. For this we had to introduce a new facility
>>> (and bus) to hold devices representing information actually
>>> provided by s390 firmware and I/O configuration.
>>>
>>> On s390 the physical structure of the pci system (bridge, bus, slot)
>>> in not shown to the OS. For this the pci bridge and bus created
>>> in qemu can also not be shown to the guest. The new zpci device class
>>> represents this abstract view on the bare pci function and allows to
>>> provide s390 specific configuration attributes for it.
>>>
>>> Sample qemu configuration:
>>> -device e1000,id=zpci1
>>> -device ne2k_pci,id=zpci2
>>> -device zpci,fid=2,uid=1248,pci_id=zpci1
>>> -device zpci,fid=17,uid=2244,pci_id=zpci2
>>>
>>> A zpci device references the corresponding PCI device via device id.
>>> The new design allows to define multiple host bridges and support more
>>> pci devices.
>>
>> Isn't this reverse? Shouldn't it rather be
>>
>>   -device zpci,...,id=zpci1
>>   -device e1000,bus=zpci1.0
>>
>> with a limit on each virtual zpci bus to only support one device?
> 
> Do you mean something like having multiple host bridges (providing a pci bus
> each) and limit the bus to just one device?
> 
> -device s390-pcihost,fid=16,uid=1234
> -device s390-pcihost,fid=17,uid=5678
> -device e1000,bus=pci.0
> -device ne2k_pci,bus=pci.1
> 
> We also discussed this option but we don't like the idea to put attributes
> belong to the pci device to the host bridge.

I guess I'm not grasping something obvious here :). What exactly are the
attributes again?


Alex