[PATCH] Document Linux's memory barriers [try #2]

[Paul Mackerras]

Matthew Wilcox writes:

> Looking at the SGI implementation, it's smarter than you think.  Looks
> like there's a register in the local I/O hub that lets you determine
> when this write has been queued in the appropriate host->pci bridge.

Given that mmiowb takes no arguments, how does it know which is the
appropriate PCI host bridge?

Paul.