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

[Ian Campbell <ian.campbell@citrix.com>]

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.

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.

> > Functions/types renamed and reindented (because apparently we do
> > that for these).
> 
> My mistake, when I first port the functions from Linux I changed the 
> name and the coding style to match the existent functions in 
> xen/common/device_tree.c
> 
> All the functions to work directly on the DT blob have been moved in a 
> separate file (arch/arm/bootfdt.c), so this file is mostly Linux code. 
> I'm thinking to resync it correctly for Xen 4.7.

That sounds good, thanks.

> 
> > Needs a selection of IORESOURCE_* defines, which I've taken from Linux
> > and have included locally for now until we figure out where else they
> > might be needed.
> 
> Regards,
>