Hello,

On Friday, August 12, 2011 2:53 PM Arnd Bergmann wrote:

On Friday 12 August 2011, Marek Szyprowski wrote:

quoted

From: Russell King <redacted>

Steal memory from the kernel to provide coherent DMA memory to drivers.
This avoids the problem with multiple mappings with differing attributes
on later CPUs.

Signed-off-by: Russell King <redacted>
[m.szyprowski: rebased onto 3.1-rc1]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

Hi Marek,

Is this the same patch that Russell had to revert because it didn't
work on some of the older machines, in particular those using
dmabounce?

Yes.
 

I thought that our discussion ended with the plan to use this only
for ARMv6+ (which has a problem with double mapping) but not on ARMv5
and below (which don't have this problem but might need dmabounce).

Ok, my fault. I've forgot to mention that this patch was almost ready 
during Linaro meeting, but I didn't manage to post it that time. Of course 
it doesn't fulfill all the agreements from that discussion.

I was only unsure if we should care about the case where CMA is not enabled
for ARMv6+ or not. This patch was prepared in assumption that 
dma_alloc_coherent should work in both cases - with and without CMA.

Now I assume that for ARMv6+ the CMA should be enabled unconditionally.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center