[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [Qemu-devel] [PATCH 2/2] xen:i386:pc_piix: create isa bridge specific to IGD passthrough

On 2014/8/31 16:58, Michael S. Tsirkin wrote:
On Fri, Aug 29, 2014 at 09:28:50AM +0800, Chen, Tiejun wrote:

On 2014/8/28 8:56, Chen, Tiejun wrote:
+     */
+    dev = pci_create_simple(bus, PCI_DEVFN(0x1f, 0),
+                            "xen-igd-passthrough-isa-bridge");
+    if (dev) {
+        r = xen_host_pci_device_get(&hdev, 0, 0, PCI_DEVFN(0x1f,
0), 0);
+        if (!r) {
+            pci_config_set_vendor_id(dev->config, hdev.vendor_id);
+            pci_config_set_device_id(dev->config, hdev.device_id);

Can you, instead, implement the reverse logic, probing
the card and supplying the correct device id for PCH?

Here what is your so-called reverse logic as I already asked you
previously? Do you mean I should list all PCHs with a combo illustrated
with the vendor/device id in advance? Then look up if we can find a




Could you explain this exactly? Then I can try follow-up your idea ASAP
if this is necessary and possible.


Could you give us some explanation for your "reverse logic" when you're


So future drivers will look at device ID for the card
and figure out how things should work from there.
Old drivers still poke at device id of the chipset for this,
but maybe qemu can do what newer drivers do:
look at the card and figure out what guest should do,
then present the appropriate chipset id.

This is based on what Jesse said:
        Practically speaking, we could probably assume specific GPU/PCH combos,
        as I don't think they're generally mixed across generations, though SNB
        and IVB did have compatible sockets, so there is the possibility of
        mixing CPT and PPT PCHs, but those are register identical as far as the
        graphics driver is concerned, so even that should be safe.


Thanks for your explanation.

so the idea is to have a reverse table mapping GPU back to PCH.
Present to guest the ID that will let it assume the correct GPU.

I guess you mean we should create to maintain such a table:

[GPU Card: device_id(s), PCH: device_id]

Then each time, instead of exposing that real PCH device id directly, qemu first can get the real GPU device id to lookup this table to present a appropriate PCH's device id to the guest.

And looks here that appropriate PCH's device id is not always a that real PCH's device id. Right? If I'm wrong please correct me.

the problem with these tables is they are hard to keep up to date

Yeah. But I think currently we can just start from some modern CPU such as HSW and BDW, then things could be easy.


Any idea to this suggestion?

as new hardware comes out, but as future hardware won't need
these hacks, we shall be fine.




matched PCH? If yes, what is that benefit you expect in passthrough
case? Shouldn't we pass these info to VM directly in passthrough case?


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.