19.4  IOC$NODE_DATA Changes to Support Non-zero
        Direct DMA Windows

  To alleviate this problem, new function codes have been added
  to ioc$node_data.  Here is a list of all the codes relating to
  direct DMA, and a description of what the data means.

  IOC$K_DIRECT_DMA_            This is the base address on the PCI
  BASE                         side, or bus address.  There is a syn-
                               onym for this function code called

                               IOC$K_DDMA_BASE_BA.
  IOC$DIRECT_DMA_SIZE      On non-Galaxy machines, this re-
                               turns the size of the direct DMA
                               window (in megabytes).  On a system
                               where the direct DMA window does
                               not start at zero, the data returned
                               is zero, implying no direct DMA
                               windows exist.

  IOC$K_DDMA_WIN_SIZE     On all systems (as of x6jh) this will
                               always return the size of the direct
                               DMA window (in megabytes).

  IOC$K_DIRECT_DMA_            This is the base physical address in
  BASE_PA                      memory of the direct DMA window. It
                               is probably closely related to mmg$gl_
                               min_node_pfn, but may be slightly
                               different due to alignment concerns.

  The address returned with the IOC$K_DIRECT_DMA_
  BASE_PA code is necessary to compute the offset.(This usu-
  ally used to be the 1Gb difference between the memory PA
  and the bus address).The offset is defined as the signed dif-
  ference between the base bus address and the base memory
  address.  This is now not necessarily 1Gb.