Re: [PATCH v4 6/6] xen: arm: Import of_bus PCI entry from Linux (as a dt_bus entry)

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

On 03/07/15 11:56, Ian Campbell wrote:
> On Fri, 2015-07-03 at 11:47 +0100, Ian Campbell wrote:
>> On Fri, 2015-06-26 at 20:08 +0200, Julien Grall wrote:
>>> Hi Ian,
>>>
>>> On 08/05/2015 13:27, Ian Campbell wrote:
>>>> This provides specific handlers for the PCI bus relating to matching
>>>> and translating. It's mostly similar to the defaults but includes some
>>>> additional error checks and other PCI specific bits.
>>>
>>> I though the previous patch (#5) was enough to handle PCI. May I ask why 
>>> we need it?
>>
>> There are some subtle differences in how the generic code vs. the pci
>> specific code here will handle buggy DTs (i.e. #*-cells which are not as
>> required by the pci bindings). This will mean we tolerate such device
>> trees better.
>>
>> I say "buggy", but actually it's not clear to me from reading "PCI Bus
>> Binding to Open Firmware" that when the device_type is "pci" that
>> #*-cells shouldn't be assumed to have the values given in that text,
>> e.g. the text says "The value of "#address-cells" for PCI Bus Nodes is
>> 3." and not "A PCI Bus Node must contain a #address-cells property
>> containing 3". Maybe that interpretation is bogus, but with this patch
>> we are are able to cope with DTs written by people who do read it like
>> that.

If the #address-cells and #size-cells are not correct that will likely
means that the property "reg" in the PCI node would be misinterpreted by
Xen.

I think it's here to cope with DT when #*-cells are not specified. The
spec doesn't say if the properties should be present or not.

>> FWIW it also gets us the ability to parse the flags (cacheability),
>> although at the moment we only check them for validity rather than use
>> them.

Good point.

> I've pasted a slightly adjusted version of this into the commit message
> for v5.

Thank you!

Regards,

-- 
Julien Grall