question about dma-ranges

[Yoder Stuart-B08248]

Mitch,

In the dma-ranges proposal:

http://playground.sun.com/1275/proposals/Closed/Accepted/410-it.txt

...there is the following special case described:

   As a special case, a "dma-ranges" property may be present in the
   root node of the device tree.  In this case, the property value
   describes the ranges of DMA addresses that the system bus can
   accept.  In this case, the length of the parent-address portion
   of each entry in the property value is 0 (because the root node
   has no parent), so the format reduces to...

A few of us in the ePAPR committee were discussing this and
were wondering what the use case for a dma-ranges on the
root is.   Is this special case really needed?

Thanks,
Stuart Yoder