Re: Introduce a want_64bit_pci support [was: PAE support]

[David Young <dyoung%pobox.com@localhost>]

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
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933