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

Tom Rini
2002-06-10T17:30:21Z

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...

--
Tom Rini (TR1265)