Messages in this thread | | | Date | Fri, 21 Oct 2016 05:53:13 -0700 | From | Christoph Hellwig <> | Subject | Re: UBIFS with dma on 4.6 kernel is not working |
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On Fri, Oct 21, 2016 at 11:29:16AM +0200, Richard Weinberger wrote: > DMA to vmalloced memory not good, it may work by chance if you transfer > less than PAGE_SIZE. > Especially on ARM.
DMA to vmalloc'ed or vmap memory is perfectly fine, you just have to be very careful.
I would suggest to not expose the vmalloc address to the lower layers that do DMA, but instead expose the pages, either as an array or scatterlist. Either allocate the pages using the normal page allocator and then use vm_map_ram to generate a virtual address for them (that is what XFS does for it's large metadata objects for example). Or if you can't do that iterate over the vmalloc address in page size chunks and use vmalloc_to_page (we still also do that for one piece of legacy cruft in XFS, but I'd rather avoid that for new designs).
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