Re: [edk2-devel] [PATCH v5 1/6] MdeModulePkg/PciHostBridge: io range is not mandatory

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,
 
> To make things worse I see that if we return success there EDK2 will
> actually go ahead and start assigning trash addresses to the device
> and enable IO space decoding in case of the PCI root port which means
> that device will try to decode invalid IO ranges.

> Logs:
> PciBus: Resource Map for Root Bridge PciRoot(0x0)
> Type =   Io16; Base = 0xFFFFFFFFFFFFFFFF; Length = 0x1000; Alignment = 0xFFF

That is wrong indeed.

I think *this* should work ...

+            } else if ((Index == TypeIo) &&
+                       (RootBridge->Io.Base == MAX_UINT64) &&
+                       (RootBridge->ResAllocNode[Index].Length == 0)) {
+              /* I/O is optional on PCIe */
+              DEBUG ((DEBUG_INFO, "Success (PCIe NoIO)\n"));

... i.e. return success only in case there are no allocation requests
for IO ranges.

> > Also note that for pcie root bridges which do support io address space
> > this patch changes nothing.
> 
> It seems to me like it does.

It doesn't.  When io address space is present the "RootBridge->Io.Base
== MAX_UINT64" check will never be true.

But the "no io address space" case was wrong indeed.

> I think to really handle it we would have to have a more involved
> change.

If we want support PCIe devices with I/O bars behind a PCIe host bridge
without I/O window, then yes.  My main focus is supporting PCIe devices
without I/O bars though.  This doesn't work currently because the code
considers a pcie host bridge without I/O window a hard failure even in
case there are no I/O allocation requests.  For fixing that the five
lines above should be enough I think.

thanks & take care,
  Gerd