On Thu, Jul 21, 2022 at 05:05:38PM +0100, Mark Cave-Ayland wrote: > On 21/07/2022 16:56, Daniel P. Berrangé wrote: > > > On Thu, Jul 21, 2022 at 04:51:51PM +0100, Mark Cave-Ayland wrote: > > > On 21/07/2022 15:28, Roman Kagan wrote: > > > > > > (lots cut) > > > > > > > In the guest (Fedora 34): > > > > > > > > [root@test ~]# lspci -tv > > > > -[0000:00]-+-00.0 Intel Corporation 82G33/G31/P35/P31 Express DRAM > > > > Controller > > > > +-01.0 Device 1234:1111 > > > > +-02.0 Red Hat, Inc. QEMU XHCI Host Controller > > > > +-05.0-[01]----00.0 Red Hat, Inc. Virtio block device > > > > +-05.1-[02]----00.0 Red Hat, Inc. Virtio network device > > > > +-05.2-[03]-- > > > > +-05.3-[04]-- > > > > +-1f.0 Intel Corporation 82801IB (ICH9) LPC Interface > > > > Controller > > > > \-1f.3 Intel Corporation 82801I (ICH9 Family) SMBus > > > > Controller > > > > > > > > Changing addr of the second disk from 4 to 0 makes it appear in the > > > > guest. > > > > > > > > What exactly do you find odd? > > > > > > Thanks for this, the part I wasn't sure about was whether the device ids > > > in > > > the command line matched the primary PCI bus or the secondary PCI bus. > > > > > > In that case I suspect that the enumeration of non-zero PCIe devices fails > > > in Linux because of the logic here: > > > https://github.com/torvalds/linux/blob/master/drivers/pci/probe.c#L2622. > > > > Just above that though is logic that handles 'pci=pcie_scan_all' > > kernel parameter, to make it look for non-zero devices. > > > > > I don't have a copy of the PCIe specification, but assuming the comment is > > > true then your patch looks correct to me. I think it would be worth > > > adding a > > > similar comment and reference to your patch to explain why the logic is > > > required, which should also help the PCI maintainers during review. > > > > The docs above with the pci=pcie_scan_all suggest it is unusual but not > > forbidden. > > That's interesting as I read it completely the other way around, i.e. PCIe > downstream ports should only have device 0 and the PCI_SCAN_ALL_PCIE_DEVS > flag is there for broken/exotic hardware :)
If someone wants to test their guest OS on exotic hardware configs, shouldn't QEMU let them make such a configuration ? Reproducing unsual hardware configs when you don't have physical access to real hardware is one of the benefits of having QEMU available. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
