On 6/20/2012 9:57 AM, Arnd Bergmann wrote:

On Tuesday 19 June 2012, Mitch Bradley wrote:

quoted

Version A - 3 address cells:  In this version, the intermediate address
space has 3 cells:  port#, address type, offset.  Address type is
    0 : root port
    1 : config space
    2 : extended config space
    3 : I/O
    4 : non-prefetchable memory
    5 : prefetchable memory.

The third cell "offset" is necessary so that the size field has a number
space that can include it.

I agree with Stephen that this is a clever way to encode all the address spaces,
very nice!

quoted

Version B - 2 address cells:  In this first version, the intermediate
address space has 2 cells:  port#, offset.  The address type (I/O, mem,
etc) is the high digit of in the offset:
     Offset 0....... : Root port
     Offset 1....... : config
     Offset 2....... : extended config
     Offset 3....... : I/O
     Offset 4....... : non-prefetchable memory
     Offset 5....... : prefetchable memory.

This is similar to how the PCI binding works internally, but I find that
a bit confusing as well, so given those two choices, I'd prefer the first
one.

Yeah, version A is my preference too.  It's straightforward and clear.  
I did the other two
versions mostly to explore the possibility space.

quoted

Version C - 2 address cells, 0 size cells (!) : In this version we hide the size component in
the intermediate space.  I don't know if that will actually work, but my guess is that it
probably would.  The intermediate address space is like version A with the omission of the
offset field.  The intermediate address just specifies the port number and the address type.

My guess is that it doesn't work with the current Linux code that transforms
the addresses. I've just recently seen the code complain about any platform
device whose parent has #size-cells=0.

	Arnd