Re: [Qemu-devel] Re: May I use -device in qemu-system command to attach to PCIe bus?

From: Markus Armbruster <armbru@redhat.com>
To: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: "Subbiah Kandasamy (skandasa)" <skandasa@cisco.com>,
	qemu-devel@nongnu.org, Wei Xu <wexu2@cisco.com>
Subject: Re: [Qemu-devel] Re: May I use -device in qemu-system command to attach to PCIe bus?
Date: Fri, 29 Oct 2010 10:02:47 +0200	[thread overview]
Message-ID: <m3zktx5suw.fsf@blackfin.pond.sub.org> (raw)
In-Reply-To: <20101028112548.GC5851@valinux.co.jp> (Isaku Yamahata's message of "Thu, 28 Oct 2010 20:25:48 +0900")

Isaku Yamahata <yamahata@valinux.co.jp> writes:

> On Thu, Oct 28, 2010 at 03:37:27AM -0700, Wei Xu wrote:
>> Isaku,
>> 
>> To make things clear, let me rephrase the problem. With q35/vPCIe, in VMM
>> monitor, we can do hotplug like:
>>  pci_add auto|<bus:dev> nic|storage
>> to hotplug a device to PCIe/PCI bus.
>> 
>> But we have two problems  here:
>> (1) command line for example, "-net nic,addr=<bus:dev>" always failed
>> because it cannot find the bus.
>> (2) If "pci_add auto" in monitor or no "addr=<bus:dev" in command line, the
>> device will be attached to PCI bus, in stead of PCIe ports
>> 
>> I solved the first problem. The root cause is pcie_root_write_config (which
>> init SECONDARY_BUS config) happened after pci_nic_init. The latter use
>> pci_find_bus to find the parent bus but failed because config space for
>> secondary bus still not initialized.
>
> Okay, now the issue is clear to me.
> When I tried to clean up pci bridge code, I included the similar lines
> in bridge initialization function.
> But Michael complained about it, so I dropped the lines for merge.
>
> I think there are two ways to address it.
> - initialize secondary/subordinate bus register by qemu
>   i.e. something like the patch below.
>
> - use qdev device path
>   i.e. qbus_find() instead of pci_find_bus().
>   I don't know if the corresponding command line option already exists or not.
>
> My preference is the former, but discussion is necessary to get consensus.
> My plan was to raise the issue when I address pv pci bus numbering issue.
> I've expected that other developers wouldn't think the issue important
> because multiple pci bus can't be used easily right now.

I'm afraid I'm missing context here.  Could you restate the problem?

New devices and buses need to work with -device / device_add.  pci_add
and -net nic are for backwards compatibility.  Folks used to them may
appreciate you making them work for PCIe.  Longer term, they should
either go away or become syntactic sugar.