Re: PCI DMA to small buffers on cache-incoherent arch

Oliver Neukum
2002-06-10T17:40:11Z

Am Montag, 10. Juni 2002 19:29 schrieb Tom Rini:
> On Mon, Jun 10, 2002 at 07:22:26PM +0200, Oliver Neukum wrote:
> > > > So is the consensus now that in general drivers should make sure
> > > > any buffers passed to pci_map/unmap are aligned to SMP_CACHE_BYTES
> > > > (and a multiple of SMP_CACHE_BYTES in size)? In other words if a
> > > > driver uses an unaligned buffer it should be fixed unless we can
> > > > prove (and document in a comment :) that it won't cause problems
> > > > on an arch without cache coherency and with a writeback cache.
> > >
> > > And how about we don't call it SMP_CACHE_BYTES too? The processors
> > > where this matters certainly aren't doing SMP...
> >
> > Definitely we should call it something different so we can limit it to
> > architectures that need it.
>
> No. We should just make it come out to a nop for arches that don't need
> it. Otherwise we'll end up with ugly things like:
> #ifdef CONFIG_NOT_CACHE_COHERENT
> ...
> #else
> ...
> #endif
>
> All over things like USB...

You are right.

Regards
Oliver