On Wed, Feb 24, 2010 at 01:19:41AM +0100, Joerg Sonnenberger wrote: > Hi, > based on the PAE discussion there is the question of what to do for > drives like twa(4). E.g. drivers that can use a more compact 32bit > layout or support the full 64bit PCI address space. > > Would it be reasonable to add a new MI variable > bool pci_use_64bit_addressing; > that gets set by MD to true if drivers should use 64bit support? > For x86, it would be enabled if physical memory above 4GB is found. > Other architectures might have similiar rules or have a IOMMU that makes > it irrelevant. The other reason for avoiding 64bit is the increased > bus traffic after all.
This seems like a property that the MD mainbus_attach() routine should set on the pcibus_attach_args before it attaches the host bridge(s). It may suffice simply to initialize pba_dmat64 to non-NULL. Dave -- David Young OJC Technologies [email protected] Urbana, IL * (217) 278-3933
