Re: Problem of initialization of platform-ehci-usb in sbsa-ref

[Peter Maydell]

On Tue, 9 May 2023 at 14:30, Gerd Hoffmann <kraxel@redhat.com> wrote:
>
>   Hi,
>
> > Gerd, is there a particular reason our EHCI controller only
> > claims to be able to do 32-bit DMA ? Should we give it a QOM
> > property so boards that only have RAM above the 4GB mark can
> > use it ? (Would the x86 PC benefit from allowing >4GB DMA?)
>
> Can be done, but it's more complex than just a property.  All
> the EHCI descriptors exist in two variants, one for 32bit and
> one for 64bit.  The current code base only supports the 32bit
> versions.
>
> Alternatives:
>   (a) use an iommu to map 32bit to 64bit dma addresses.
>   (b) use xhci instead of ehci.
>
> I'd recommend (b) as the xhci hardware design is much more
> virtualization-friendly.

Thanks. Leif, do you have any preference there?

-- PMM