Marek,

It looks that You have simplified arm_iommu_map_sg() function too much. 
The main advantage of the iommu is to map scattered memory pages into 
contiguous dma address space. DMA-mapping is allowed to merge consecutive
entries in the scatter list if hardware supports that.
http://article.gmane.org/gmane.linux.kernel/1128416

I would update arm_iommu_map_sg() back to coalesce the sg list.

I'm not sure if mmc drivers are aware of coalescing the SG entries together.
If not the code must be updated to use dma_sg_len() and the dma entries
number returned from dma_map_sg() call.

MMC drivers seem to be aware of coalescing the SG entries together as they are using dma_sg_len().

Let me test and update the patch.

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nvpublic