Re: [Qemu-devel] [PATCH] spapr-pci: enable adding PHB via -device

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 01/21/2014 06:56 PM, Markus Armbruster wrote:
> Alexey Kardashevskiy <aik@ozlabs.ru> writes:
> 
>> On 01/21/2014 02:27 AM, Markus Armbruster wrote:
>>> Alexey Kardashevskiy <aik@ozlabs.ru> writes:
>>>
>>>> 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).
>>>
>>> Specifically:
>>>
>>> commit 837d37167dc446af8a91189108b363c04609e296
>>> Author: Markus Armbruster <armbru@redhat.com>
>>> Date:   Thu Nov 28 17:26:55 2013 +0100
>>>
>>>     sysbus: Set cannot_instantiate_with_device_add_yet
>>>     
>>>     device_add plugs devices into suitable bus.  For "real" buses, that
>>>     actually connects the device.  For sysbus, the connections need to be
>>>     made separately, and device_add can't do that.  The device would be
>>>     left unconnected, and could not possibly work.
>>>     
>>>     Quite a few, but not all sysbus devices already set
>>>     cannot_instantiate_with_device_add_yet in their class init function.
>>>     
>>>     Set it in their abstract base's class init function
>>>     sysbus_device_class_init(), and remove the now redundant assignments
>>>     from device class init functions.
>>>     
>>>     Signed-off-by: Markus Armbruster <armbru@redhat.com>
>>>     Reviewed-by: Marcel Apfelbaum <marcel.a@redhat.com>
>>>     Signed-off-by: Andreas Färber <afaerber@suse.de>
>>>
>>> Always good to point to specific commits in commit messages instead of
>>> hand-waving "recent changes".
>>
>>
>> My bad, I'll do this next time. Just lost myself in that patch series.
>>
>>
>>>> This brings the capability back and puts SPAPR PHB into "bridge"
>>>> category.
>>>
>>> Look, a sysbus device that grabs the resources it needs from its init()
>>> callback instead of getting connected to them by the code that creates
>>> it!  I'm not sure that's proper, but if it works...  Maybe Andreas
>>> (cc'ed) can advise.
>>
>> Sorry, I am not following you. SPAPR PHB allocates resources (memory
>> regions...) as (for example) E1000 ethernet device does.
> 
> "Resources" was a poor choice of word.
> 
> I'm talking about connections to other devices.  An ordinary device on a
> proper bus like PCI or USB gets all its connections via its bus.  The
> "sysbus" doesn't provide any connection opportunities for its devices.
> Instead, the connections are made by the code creating the device.
> 
> You tell me "-device spapr-pci-host-bridge" works (with your patch).
> That either means it doesn't need any such connections, or it sets them
> up itself somehow, or I'm missing something.  The first two would be
> unusual, the latter not so much :)


It maps itself (MMIO/IO windows) into the guest physical RAM at some
predefined addresses which are calculated from its @index property, and
that is pretty much it. I am not sure what else connections it might ever
need :) The rest is done via platform hyper- or rtas-calls, and this is
that connection I guess.



-- 
Alexey