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. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
