Re: RFC: being more anal about iospace accesses..

[Jesse Barnes <jbarnes@engr.sgi.com>]

On Thursday, September 16, 2004 1:04 pm, David S. Miller wrote:
> On Thu, 16 Sep 2004 11:52:54 -0700
>
> Jesse Barnes <jbarnes@engr.sgi.com> wrote:
> > On Thursday, September 16, 2004 11:21 am, Linus Torvalds wrote:
> > > It's literally only the sn2 _platform_ that does something stupid. In
> > > other words, it's not ia64 that is broken (surprise surprise - you
> > > never expected me to have said anything good about ia64), it's
> > > literally the SN2 platform that seems broken.
> >
> > No, it's just the only smart platform.  Apparently we're the only ones
> > who realized that most PIO reads do not rely on prior DMA being complete
> > (and that it's expensive to make sure that they do), so we optimized that
> > out of our hardware.  Only interrupts will guarantee DMA completion on
> > SGI platforms.
>
> Jesse, I think you might not need that hack in the I/O accessor
> routines to handle this.  pci_dma_unmap(), pci_dma_sync_*() and
> friends should be the place to perform this "prior DMA sync" thing.

That would be ok, except for the fact that we wouldn't be able to provide 
'consistent' memory.  I think it's better to implement the expected PCI 
semantics but provide an out via the _relaxed interface (new interfaces 
aside).

Jesse