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

On Wed, Aug 05, 2015 at 09:03:06PM +0800, 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?
> If the hardware has mmio region not described in the ACPI, how does the
> driver know the region and use it?

On the x86 world we would query the PCI configuration registers and read
the device BAR registers. Those would contain the MMIO regions the
device uses.

But x86 is funny and you do say 'many .. ARM .. have non-PCI buses' - which
would imply you have not hit this yet.

Are PCI devices interrogated differently on ARM? No configuration registers?
> >Does the driver would have to call a specific xen function to register
> >the missing I/O?
> -- 
> Shannon
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