[PATCH 03/14] bus: mvebu-mbus: Introduce device tree binding

On Friday 07 June 2013, Jason Gunthorpe wrote:

We have a minimum requirement that the bootloader setup internal regs,
so the minimum required DT bindings is going to be this:

mbus {
  compatible = ...
  ranges = <INTERNAL_REGS_MAP_ID 0xf1000000 0x100000>;
  reg = <0xf1000xxx ...>; // MBUS regs block
  #address/size-cells...

  internal-regs  {
      ranges = <0 INTERNAL_REGS_MAP_ID 0x100000>;
  }
}

ie the ranges should never be empty.

Right, that's what I thought.

Discovery of the address of the mbus control registers is via the reg
property on its own node (which is untranslated), and all other
internal regs blocks will automatically translate as they are supposed
to (Thomas's work to make internal regs 0xd/0xf1 relies on this, AFAIK)

INTERNAL_REGS_MAP_ID is an invalid target ID value, defined to mean
the internal registers target. 0xFFFFFFFF is a better choice for this
than 0, because 0xFFFFFFFF is never going to be a valid target id, it
is too large.

Can you explain to me why it is an invalid target ID value? Is it
treated very differently by the mbus register setup than all the
others? I guess we can define it as something else to make a valid
target ID, by using one or more of the remaining bits in the first
address cell.

	Arnd