Hi, > > +Plug only legacy PCI devices as Root Complex Integrated Devices > > +even if the PCIe spec does not forbid PCIe devices. > > I suggest "even though the PCI Express spec does not forbid PCI Express > devices as Integrated Devices". (Detail is good!)
While talking about integrated devices: There is docs/q35-chipset.cfg, which documents how to mimic q35 with integrated devices as close and complete as possible. Usage: qemu-system-x86_64 -M q35 -readconfig docs/q35-chipset.cfg $args Side note for usb: In practice you don't want to use the tons of uhci/ehci controllers present in the original q35 but plug xhci into one of the pcie root ports instead (unless your guest doesn't support xhci). > > +as required by PCI spec will reserve a 4K IO range for each. > > +The firmware used by QEMU (SeaBIOS/OVMF) will further optimize > > +it by allocation the IO space only if there is at least a device > > +with IO BARs plugged into the bridge. > > This used to be true, but is no longer true, for OVMF. And I think it's > actually correct: we *should* keep the 4K IO reservation per PCI-PCI bridge. > > (But, certainly no IO reservation for PCI Express root port, upstream > port, or downstream port! And i'll need your help for telling these > apart in OVMF.) IIRC the same is true for seabios, it looks for the pcie capability and skips io space allocation on pcie ports only. Side note: the linux kernel allocates io space nevertheless, so checking /proc/ioports after boot doesn't tell you what the firmware did. cheers, Gerd
