Re: [PATCH v2 4/5] iommu: Use dma_addr_t for IOVA arguments

[Arnd Bergmann]

On Tuesday 06 May 2014 16:48:40 Bjorn Helgaas wrote:
> Convert the "iova" arguments of iommu_map(), iommu_unmap(), etc., from
> "unsigned long" to dma_addr_t.
> 
> bb5547acfcd8 ("iommu/fsl: Make iova dma_addr_t in the iommu_iova_to_phys
> API") did this for iommu_iova_to_phys(), but didn't fix the rest of the
> IOMMU API.

This patch looks 100% correct, but I'm not convinced it's a good idea:
On 32-bit platforms (i.e. most of the ones you change), doing 64-bit
arithmetic has a noticeable overhead. I am not aware of an IOMMU that
actually uses 64-bit DMA addresses on its slave side, usually they
are used to translate addresses from 32-bit masters into 64-bit
memory addresses, so using 'unsigned long' seems better from a practical
point of view as opposed to the strict type correctness.

	Arnd
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