Re: [PATCH v2 07/10] ARM: tegra: pcie: Add device tree support

[Mitch Bradley <wmb@firmworks.com>]

On 6/20/2012 6:32 AM, Stephen Warren wrote:
> On 06/19/2012 03:31 PM, Mitch Bradley wrote:
> ...
>
>
> The third cell "offset" is necessary so that the size field has a number
> space that can include it.
>
> Can you expand on that sentence a bit more; I don't quite understand
> that aspect. Thanks.

The meaning of "size"(in the context of "reg" which is phys,size) is 
"the device occupies a
contiguous sequence of addresses beginning at phys and continuing to 
phys+size-1". The
implicit addition occurs on the last #size-cells cells of the phys.

Suppose you have 2-cell phys where the values for different devices are 
<0 0>, <0 1>, <0 2>, <1 0>, <1 1>,
<1 2>.  The first number is the port number and the second is address 
space type.  It doesn't make
sense to say that size is 0x8000, because that would imply that the 
device extends from, say,
<1 2> to <1 0x8001>.

I'm not sure this is written down anywhere as explicitly as above, but 
it is certainly implicit
in the way that ranges properties work, and it is certainly part of the 
mental model that
was in my head when I developed the device tree addressing scheme.