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

[Alexey Kardashevskiy]

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".

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? :)


-- 
Alexey