DMA coherency in drivers/tty/serial/mpsc.c

[Christoph Hellwig]

On Tue, Jun 25, 2019 at 09:37:22AM -0700, Mark Greer wrote:
> Yeah, the mpsc driver had lots of ugly cache related hacks because of
> cache coherency bugs in the early version of the MV64x60 bridge chips
> that it was embedded in.  That chip is pretty much dead now and I've
> removed core support for it from the powerpc tree.  Removing the mpsc
> driver is on my todo list but I've been busy and lazy.  So, to sum it
> up, don't spend any more time worrying about it as it should be removed.
> 
> I'll post a patch to do that tonight and I'm sorry for any time you've
> spent looking at it so far.

No problem.  And if future such broken chips show up we now have
support for per-device DMA coherency settings and could actually
handle it in a reaѕonably clean way.