Re: [PATCH v6 1/3] iommu: Implement common IOMMU ops for DMA mapping

[Mark Hounschell <markh-n2QNKt385d+sTnJN9+BGXg@public.gmane.org>]

On 10/30/2015 10:09 AM, Joerg Roedel wrote:
> On Fri, Oct 30, 2015 at 09:17:52AM +0800, Daniel Kurtz wrote:
>> Hmm, I thought the DMA API maps a (possibly) non-contiguous set of
>> memory pages into a contiguous block in device memory address space.
>> This would allow passing a dma mapped buffer to device dma using just
>> a device address and length.
>
> If you are speaking of the dma_map_sg interface, than there is absolutly
> no guarantee from the API side that the buffers you pass in will end up
> mapped contiguously.
> IOMMU drivers handle this differently, and when there is no IOMMU at all
> there is also no way to map these buffers together.
>

That is what CMA is for ya know. It makes it physically contiguous.

Mark