The PPC476GTR SoC supports message signalled interrupts (MSI) by writing to special addresses within the High Speed Transfer Assist (HSTA) module. This patch adds support for PCI MSI with a new system device. The DMA window is also updated to allow access to the entire 42-bit address range to allow PCI devices write access to the HSTA module. Signed-off-by: Alistair Popple <alistair@popple.id.au> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>