Hi Franklin,

On Thu, 10 Mar 2016 17:56:42 -0600
Franklin S Cooper Jr [off-list ref] wrote:

Based on DMA documentation and testing using high memory buffer when
doing dma transfers can lead to various issues including kernel
panics.

I guess it all comes from the vmalloced buffer case, which are not
guaranteed to be physically contiguous (one of the DMA requirement,
unless you have an iommu).

To workaround this simply use cpu copy. The amount of high memory
buffers used are very uncommon so no noticeable performance hit should
be seen.

Hm, that's not necessarily true. UBI and UBIFS allocate their buffers
using vmalloc (vmalloced buffers fall in the high_memory region), and
those are likely to be dis-contiguous if you have NANDs with pages > 4k.

I recently posted patches to ease sg_table creation from any kind of
virtual address [1][2]. Can you try them and let me know if it fixes
your problem?

Thanks,

Boris

[1]https://lkml.org/lkml/2016/3/8/276
[2]https://lkml.org/lkml/2016/3/8/277


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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