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

[Wei Xu]

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.

The fix is like:

address@hidden contents]$ git diff hw/pci_bridge.c
diff --git a/hw/pci_bridge.c b/hw/pci_bridge.c
index c048305..042c1f9 100644
--- a/hw/pci_bridge.c
+++ b/hw/pci_bridge.c
@@ -203,6 +203,7 @@ void pci_bridge_set_bus_number(PCIBridge *br,
     uint16_t domain;
     uint8_t primary_bus;
     uint8_t devfn;
+    uint8_t *conf;
 
     if (!pci_bus_number) {
         pci_bus_number = qemu_mallocz(sizeof(*pci_bus_number));
@@ -215,10 +216,15 @@ void pci_bridge_set_bus_number(PCIBridge *br,
 
     d = &br->dev;
     devfn = d->devfn;
+       conf = d->config;
 
     br->sec_bus = secondary;
     br->sub_bus = subordinate;
 
+       //TODO wexu2 workaround of "-net nic,addr=<bus:dev>"
+    pci_set_byte(conf + PCI_SECONDARY_BUS, secondary);
+    pci_set_byte(conf + PCI_SUBORDINATE_BUS, subordinate);
+
     bus = d->bus;
     primary_bus = 0;
     if ((d = pci_bridge_get_device(bus)) != NULL){

The fix is a little bit hacky -- welcome any advice.

For 2nd issue, current code assume PCI bus is flat and not straight forward
to change the behavior.

Wei Xu


On 10/27/10 10:16 PM, "Isaku Yamahata" <address@hidden> wrote:

> Oh, now I'm seeing your point. Some codes of qemu assume that
> the pci bus is flat. They need fixes.
> 
> Right now I've found
> - parse_pci_devfn in qdev-properties.c
>   This corresponds to (1)
> - pci_get_bus_devfn() in pci.c
>   This corresponds to (2)
> 
> thanks,
> 
> On Wed, Oct 27, 2010 at 08:51:29PM -0700, Wei Xu wrote:
>> Isaku,
>> 
>> I found two issues:
>> (1) command line option is not working: even with addr=<bus>, it complained
>> bus cannot be found;
>> (2) monitor: pci_add auto ... cannot work.
>> 
>> Wei
>> 
>> 
>> On 10/27/10 8:03 PM, "Isaku Yamahata" <address@hidden> wrote:
>> 
>>> On Wed, Oct 27, 2010 at 09:51:47AM -0700, Wei Xu wrote:
>>>> Isaku,
>>>> 
>>>> I have one question regarding EP and PCIe bus: now only way is to use
>>>> "pci_add <bus:dev> .." to hot-plug the device to a PCIe port. Looks like
>>>> command line with -device parameter automatically use PCI bus? Is it
>>>> possible to support it? Have to provide the <bus:dev> in -device parameter?
>>> 
>>> I'm not sure I got your question right.
>>> We can populate the device under an express port with -device command line
>>> option. At least it should be possible.
>>> 
>>> For implementation detail, qemu doesn't distinguish pci express
>>> from conventional pci so strictly.
>>> The only difference is whether the bridge(pci host bridge or
>>> pci-to-pci bridge) is just express port because I implemented express
>>> ports as pci-to-pci bridge.
>>> 
>>> Or do you want to add express port with command line option?
>>> If so, not possible at the moment.
>>