Re: Design doc of adding ACPI support for arm64 on Xen

[Julien Grall <julien.grall@citrix.com>]

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.

Regards,

-- 
Julien Grall