On Tue, Aug 19, 2014 at 10:52:46PM +0200, Laurent Pinchart wrote: > On Tuesday 19 August 2014 11:40:24 Olav Haugan wrote: > > On 8/19/2014 9:11 AM, Laurent Pinchart wrote: > > > On Tuesday 19 August 2014 13:59:54 Joerg Roedel wrote: > > >> On Mon, Aug 18, 2014 at 03:47:56PM -0700, Olav Haugan wrote: > > >>> If the alignment is not correct then iommu_map() will return error. Not > > >>> sure what other option we have here (and why make it different behavior > > >>> than iommu_map which just return error when it is not aligned properly). > > >>> I don't think we want to force any kind of alignment automatically. I > > >>> would rather have the API tell me I am doing something wrong than having > > >>> the function aligning the values and possibly undermap or overmap. > > >> > > >> But sg->offset is an offset into the page (at least it is used that way > > >> in the DMA-API and since you do 'page_len = s->offset + s->length' you > > >> use it the same way). > > >> So when you pass iova + offset the result will no longer be > > >> page-aligned. You should force sg->offset == 0 and sg->length to be > > >> page-aligned instead. This makes more sense because the IOMMU-API works > > >> on (io)-page granularity and not on arbitrary phys-addr ranges like the > > >> DMA-API. > > >> > > >>> Yes, I am aware of that. However, several people prefer this than > > >>> passing in scatterlist. It is not very convenient to pass a scatterlist > > >>> in some use cases. Someone mentioned a use case where they would have to > > >>> create a dummy sg list and populate it with the iova just to do an > > >>> unmap. I believe we would have to do this also. There is no use for > > >>> sglist when unmapping. However, would like to keep separate API from > > >>> iommu_unmap() to keep the API function names symmetric > > >>> (map_sg/unmap_sg). > > >> > > >> Keeping it symetric is not more complicated, the caller just needs to > > >> keep the sg-list used for mapping around. I prefer the unmap_sg call to > > >> work in sg-lists too. > > > > > > Do we have a use case where the unmap_sg() implementation would be > > > different than a plain iommu_unmap() call ? If not I'd rather remove > > > unmap_sg() completely. > > > > > >>> I thought that was why we added the default fallback and set all the > > >>> drivers to point to these fallback functions. Several people wanted this > > >>> so that we don't have to have NULL-check in these functions (and have > > >>> the functions be simple inline functions). > > >> > > >> Okay, since you add these call-backs to all drivers I think I can live > > >> with not doing a pointer check here. > > > > > > I suggested doing a > > > > > > if (ops is not NULL) > > > > > > return ops(); > > > > > > else > > > > > > return default_ops(); > > > > > > to avoid modifying all drivers. I'm not sure why that wasn't received with > > > much enthusiasm. > > > > Both Thierry R. and Konrad W. argued for modifying the drivers instead > > so I implemented what the majority wanted. :-) > > I'm not blaming you :-) I was just wondering what their rationale was. In my opinion it's much more direct that way. It means that if a driver doesn't implement it, it won't fall back to some default implementation instead. Providing an explicit helper like this makes it obvious that the driver is using a default implementation rather than making things work "magically". It's easier to see in the driver that there's the potential to optimize. It also has the side-effect of keeping the core code cleaner in my opinion, since the core iommu_map_sg() and iommu_unmap_sg() functions can now blindly call into drivers directly rather than performing the various checks to see if they implement the required functionality. Thierry
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