Re: pci_mapreg_map(9) and prefetchable BARs

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

On Tue, Aug 09, 2011 at 05:38:43PM -0400, Michael wrote:
> Hello,
> 
> Why would it fail if the BAR is marked as prefetchable but someone
> requests a non-prefetchable mapping? The bit is just a hint.

My phrasing was probably awkward.  It wouldn't fail in that case.

Here's the proposal:

1 Safety first: pci_mapreg_map() should map every BAR as
  if it is non-prefetchable (i.e., non-cached, non-write
  combining, order enforced) unless the caller passes the hint
  BUS_SPACE_MAP_PREFETCHABLE.

2 pci_mapreg_map() should turn on caching, write-combining, et cetera,
  on a prefetchable BAR if the caller passes BUS_SPACE_MAP_PREFETCHABLE.

3 pci_mapreg_map() should return 1 (indicating an error) before it
  violates #1.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 344-0444 x24