On Thu, 2 Jun 2022 at 15:15, Gerd Hoffmann <kra...@redhat.com> wrote:
>
> Hi,
>
> > I did a quick test with both ArmVirtQemu and microvm (using this
> > series but omitting the MdeModulePkg), and I can confirm that not
> > having a I/O resource window at all seems to work fine if none of the
> > PCI devices have I/O BARs.
> >
> > Gerd, do you remember why exactly this patch is needed? Is it related
> > to devices that have I/O BARs but don't actually require them to
> > function correctly?
>
> Well, the difference seem to be pcie root ports. When plugging my
> virtio device into the root bus everything is fine:
>
> PCI Bus First Scanning
> PciBus: Discovered PCI @ [00|00|00]
>
> PciBus: Discovered PCI @ [00|01|00]
> BAR[1]: Type = Mem32; Alignment = 0xFFF; Length = 0x1000;
> Offset = 0x14
> BAR[4]: Type = PMem64; Alignment = 0x3FFF; Length = 0x4000;
> Offset = 0x20
> [ ... ]
> PciHostBridge: NotifyPhase (AllocateResources)
> RootBridge: PciRoot(0x0)
> Mem64: Base/Length/Alignment = 6000000000/100000/FFFFF - Success
> Mem: Base/Length/Alignment = C0000000/100000/FFFFF - Success
> PciBus: HostBridge->NotifyPhase(AllocateResources) - Success
>
> When plugging the virtio device into a pcie root port it doesn't work
> and the log looks like this:
>
> PCI Bus First Scanning
> PciBus: Discovered PCI @ [00|00|00]
>
> PciBus: Discovered PPB @ [00|08|00]
> Padding: Type = Mem32; Alignment = 0x1FFFFF; Length = 0x200000
> Padding: Type = Io; Alignment = 0x1FF; Length = 0x200
> BAR[0]: Type = Mem32; Alignment = 0xFFF; Length = 0x1000;
> Offset = 0x10
>
> PciBus: Discovered PCI @ [01|00|00]
> BAR[1]: Type = Mem32; Alignment = 0xFFF; Length = 0x1000;
> Offset = 0x14
> BAR[4]: Type = PMem64; Alignment = 0x3FFF; Length = 0x4000;
> Offset = 0x20
> [ ... ]
> PciHostBridge: NotifyPhase (AllocateResources)
> RootBridge: PciRoot(0x0)
> Mem: Base/Length/Alignment = C0000000/300000/1FFFFF - Success
> Mem64: Base/Length/Alignment = 6000000000/100000/FFFFF - Success
> I/O: Base/Length/Alignment = FFFFFFFFFFFFFFFF/1000/FFF - Out Of Resource!
> [ ... ]
> PciHostBridge: NotifyPhase (AllocateResources)
> RootBridge: PciRoot(0x0)
> Mem64: Base/Length/Alignment = 6000000000/100000/FFFFF - Success
> Mem: Base/Length/Alignment = C0000000/200000/FFFFF - Success
> I/O: Base/Length/Alignment = FFFFFFFFFFFFFFFF/0/FFF - Out Of Resource!
>
> So, it's apparently the io window of the pcie root port which causes
> edk2 try allocate io resources.
>
This seems to be related to the padding logic, i.e., we are trying to
preserve some extra I/O space for the root port in case we hotplug
something that might need it.
The hack below gets around this - we'll need something suitable check
here that avoids I/O padding when the root port has not I/O resource
window in the first place. Care to cook something up?
--- a/OvmfPkg/PciHotPlugInitDxe/PciHotPlugInit.c
+++ b/OvmfPkg/PciHotPlugInitDxe/PciHotPlugInit.c
@@ -733,7 +733,7 @@ GetResourcePadding (
}
}
- if (DefaultIo) {
+ if (DefaultIo && FALSE) {
//
// Request defaults.
//
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