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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.

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