Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 5 Aug 2015, Stefano Stabellini wrote:
> On Wed, 5 Aug 2015, Julien Grall wrote:
> > On 05/08/15 14:03, Shannon Zhao wrote:
> > > 
> > > 
> > > On 2015/8/5 20:48, Julien Grall wrote:
> > >> On 05/08/15 12:49, Shannon Zhao wrote:
> > >>>> >>That's great!
> > >>>> >>Keep in mind that many ARM platforms have non-PCI busses, so I think
> > >>>> >>we'll need an amba and a platform bus_notifier too, in addition to
> > >>>> the
> > >>>> >>existing pci bus notifier.
> > >>>> >>
> > >>> >
> > >>> >Thanks for your reminding. I thought about amba. Since ACPI of current
> > >>> >linux kernel doesn't support probe amba bus devices, so this
> > >>> >bus_notifier will not be used at the moment. But there are some voice
> > >>> >that we need to make ACPI support amba on the linux arm kernel mail
> > >>> >list. And to me it doesn't matter to add the amba bus_notifier.
> > >> This comment raised one question. What happen if the hardware has MMIO
> > >> region not described in the ACPI?
> > >>
> > > This sounds weird. If a device is described in ACPI table, it will not
> > > describe the MMIO region which the driver will use? Does this situation
> > > exist?
> > 
> > Buggy ACPI tables, not possible to describe the ACPI ... There is plenty
> > of reason.
> > 
> > I don't know if there is current problem on ACPI (I don't have much work
> > with it). But it presents on the device tree. We may a lots of specific
> > platform mapping in Xen (see specific_mapping) because of buggy DT.
> > 
> > We can't rule out and needs to provide a way to cope with this. If we
> > don't do it, it will fall on us sooner or later.
> > 
> > > If the hardware has mmio region not described in the ACPI, how does the
> > > driver know the region and use it?
> > 
> > Hardcoded.
> 
> I wouldn't worry about buggy drivers or tables for now.
> 
> I think that the Linux maintainers should take care of that by refusing
> to merge any drivers that do such a thing anyway.

If worse comes to worst, we can do the mapping from the platform file in
Xen, which is bad, but would be appropriate to work around buggy
firmware.

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