[Bug 1900918] [NEW] PXB devices

[bwidawsk]

Public bug reported:

release: 4c41341af76cfc85b5a6c0f87de4838672ab9f89

qdev_device_add() will search for the "closest" bus possible, and bail out 
early if that bus is a root bus. pxb devices are considered root buses and so 
if you either
1. Add a PCI device on the QEMU command line *after* a pxb device, or
2. Add an integrated PCI device (like a watchdog)

#1: -device pxb-pcie,id=cxl.0,bus=pcie.0,bus_nr=52 -device 
ahci,id=sata0,addr=0x8
#2: -watchdog i6300esb -device pxb-pcie,id=cxl.0,bus=pcie.0,bus_nr=52

The PXB will get selected as the bus (instead of the real root bus) and
this will cause an assertion failure with the message like "qemu-system-
x86_64: -device ahci,id=sata0,addr=0x8: PCI: Only PCI/PCIe bridges can
be plugged into pxb-pcie"

I think this is relatively solvable in the code base by determining if a
bus is an expander, and skipping it if so. However, I wonder if it makes
more sense to just allow expanders to have endpoint devices.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1900918

Title:
  PXB devices

Status in QEMU:
  New

Bug description:
  release: 4c41341af76cfc85b5a6c0f87de4838672ab9f89

  qdev_device_add() will search for the "closest" bus possible, and bail out 
early if that bus is a root bus. pxb devices are considered root buses and so 
if you either
  1. Add a PCI device on the QEMU command line *after* a pxb device, or
  2. Add an integrated PCI device (like a watchdog)

  #1: -device pxb-pcie,id=cxl.0,bus=pcie.0,bus_nr=52 -device 
ahci,id=sata0,addr=0x8
  #2: -watchdog i6300esb -device pxb-pcie,id=cxl.0,bus=pcie.0,bus_nr=52

  The PXB will get selected as the bus (instead of the real root bus)
  and this will cause an assertion failure with the message like "qemu-
  system-x86_64: -device ahci,id=sata0,addr=0x8: PCI: Only PCI/PCIe
  bridges can be plugged into pxb-pcie"

  I think this is relatively solvable in the code base by determining if
  a bus is an expander, and skipping it if so. However, I wonder if it
  makes more sense to just allow expanders to have endpoint devices.

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