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.