Re: What's up with cpu_is_noncoherent_r10000() ?

[tsbogend@alpha.franken.de (Thomas Bogendoerfer)]

On Mon, Aug 25, 2008 at 09:34:29AM -0700, David Daney wrote:
> What is the reasoning for only doing the cache operation on  R10K based 
> systems?

non coherent R10k need after DMA operations to get rid of remains
of load/store speculations. Other CPUs don't pollute the cache
after it got flushed.

But this optimization is wrong, we need to do the flush for
every non coherent device otherwise polling a descriptor via
a cached mapping can't work. And this exactly what E100 does.

Instead of if (cpu_is_noncoherent_r10000(deva)) something like

if (cpu_is_noncoherent_r10000(dev) || 
    (!plat_device_is_coherent(dev) && (direction != DMA_TO_DEVICE)))


should do the trick with minimum flushes for non R10k CPUs. But probably
a simple

if ((!plat_device_is_coherent(dev))

is the safest approach.

Thomas.

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