Re: [Qemu-ppc] [Qemu-devel] Why is "spapr-pci-host-bridge" no-user?

[Alexey Kardashevskiy]

On 03/06/16 21:36, Markus Armbruster wrote:
> Alexey Kardashevskiy <address@hidden> writes:
> 
>> On 03/06/16 16:40, Markus Armbruster wrote:
>>> Commit 09aa9a5 "spapr-pci: enable adding PHB via -device" set
>>> cannot_instantiate_with_device_add_yet without also adding a comment
>>> explaining why.  It is currently the only one lacking such a comment.
>>> Let's fix that.
>>>
>>> Unfortunately, the commit message doesn't tell me (or I'm too dense to
>>> understand it):
>>>
>>>     spapr-pci: enable adding PHB via -device
>>>     
>>>     Recent changes introduced cannot_instantiate_with_device_add_yet
>>>     and removed capability of adding yet another PCI host bridge via
>>>     command line for SPAPR platform (POWERPC64 server).
>>>     
>>>     This brings the capability back and puts SPAPR PHB into "bridge"
>>>     category.
>>>     
>>>     This is not much use for emulated PHB but it is absolutely required
>>>     for VFIO as we put an IOMMU group onto a separate PHB on SPAPR.
>>>     
>>>     Signed-off-by: Alexey Kardashevskiy <address@hidden>
>>>     Signed-off-by: Alexander Graf <address@hidden>
>>>
>>> Alexey, can you explain why the device cannot be used with -device /
>>> device_add?
>>
>> It can be used with "-device" with as it is today, i.e. with
>> "cannot_instantiate_with_device_add_yet=false".
> 
> I misread the code.  But the assignment needs an explanation anyway :)

imho at that moment it was pretty valid :) Now we do not even have to have
multiple PHBs on spapr, although we still support this ;)

> 
>> With "cannot_instantiate_with_device_add_yet=true", I get this:
>>
>> qemu-system-ppc64: -device spapr-pci-host-bridge,id=phb10,index=10:
>> Parameter 'driver' expects pluggable device type
>>
>>
>> At that moment (sha1 09aa9a526a86fd2e380e86^) it failed because of
>> inherited "cannot_instantiate_with_device_add_yet=true" from
>> sysbus_device_class_init() (which is gone now):
>>
>> qemu-system-ppc64: -device spapr-pci-host-bridge,id=phb10,index=10:
>> Parameter 'driver' expects pluggable device type
>>
>> So there was my patch.
>>
>>
>> "device_add" is different, it does not work because:
>> (qemu) device_add spapr-pci-host-bridge
>> Bus 'main-system-bus' does not support hotplugging
>>
>> Which I am not sure if it is true for all platforms or just spapr/ppc64 but
>> I do not care much now as there is some work to do anyway to support PHB
>> hotplug as per LoPAPR specification anyway.
>>
>> Does this help? :)
> 
> Now you made me read the code more carefully, I have different
> questions.
> 
> Can we delete the assignment?  -device
> spapr-pci-host-bridge,id=phb10,index=10 still works for me then.


_Now_ we can indeed as the default has changed, this works for me too, I
just forgot to mention this, sorry.


> 
> If not, why?
> 


-- 
Alexey