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

["Ard Biesheuvel" <ardb@kernel.org>]

On Fri, 29 Apr 2022 at 08:50, Gerd Hoffmann <kraxel@redhat.com> wrote:
>
> On Wed, Apr 27, 2022 at 03:08:50AM +0000, Ni, Ray wrote:
> > Ard,
> > can you explain more?
> >
> > Your code changes the PciHostBridge driver to ignore the failure of IO allocation.
> > If IO requirement of certain PCI(E) devices can be ignored, can you change the IncompatiblePciDevice protocol implementation to override the IO request from the devices?
>
> Hmm, it's a problem indeed, device initialization fails in case an
> io bar is present even if the bar is not required to drive the device.
>

I'd say the risk for regressions is rather low, though, given that it
only affects configurations that would fail PCI resource allocation
today. Or am I missing something?

In any case, the PCIe spec is clear about this: I/O space is optional,
and we need to incorporate this into the generic code at *some* point.
It makes no sense for every individual platform to keep adding these
hacks.

> Suggestions how to deal with this best?  ovmf has it's own
> IncompatiblePciDevice Protocol implementation, so I could
> handle it there because only OvmfPkg/Microvm needs this.
>
> Or should the MdeModulePkg version be updated too?
>

I'd say we do both, to avoid stalling your series forever :-)