The tag enforces a single restriction that all DMA transactions must not
cross a 4GB boundary. Note that while this restriction technically only
applies to PCI-express, this change applies it to all PCI devices as it
is simpler to implement that way and errs on the side of caution.
- Add a softc structure for PCI bus devices to hold the bus_dma tag and
a new pci_attach_common() routine that performs actions common to the
attach phase of all PCI bus drivers. Right now this only consists of
a bootverbose printf and the allocate of a bus_dma tag if necessary.
- Adjust all PCI bus drivers to allocate a PCI bus softc and to call
pci_attach_common() from their attach routines.
MFC after: 2 weeks
1b1596a3b3