Re: [PATCH] iommu: Do physical merging in iommu_map_sg()

[Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

On Thu, Oct 04, 2018 at 04:47:37PM +0100, Robin Murphy wrote:
> The original motivation for iommu_map_sg() was to give IOMMU drivers the
> chance to map an IOVA-contiguous scatterlist as efficiently as they
> could. It turns out that there isn't really much driver-specific
> business involved there, so now that the default implementation is
> mandatory let's just improve that - the main thing we're after is to use
> larger pages wherever possible, and as long as domain->pgsize_bitmap
> reflects reality, iommu_map() can already do that in a generic way. All
> we need to do is detect physically-contiguous segments and batch them
> into a single map operation, since whatever we do here is transparent to
> our caller and not bound by any segment-length restrictions on the list
> itself.
> 
> Speaking of efficiency, there's really very little point in duplicating
> the checks that iommu_map() is going to do anyway, so those get cleared
> up in the process.
> 
> Signed-off-by: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>

I like the idea, but I find the goto usage to jump back into the just
terminated loop highly confusing.  Would it be that much worse to simply
duplicate the iommu_map call?