On Fri, Jul 05, 2024 at 08:39:10AM +0200, Christoph Hellwig wrote: > Review from the NVMe driver consumer perspective. I think if all these > were implement we'd probably end up with less code than before the > conversion. Thanks for the review, I will try to address all the comments in the next version. > > The split between dma_iova_attrs, dma_memory_type and dma_iova_state is > odd. I would have expected them to just be just a single object. While > talking about this I think the domain field in dma_iova_state should > probably be a private pointer instead of being tied to the iommu. > > Also do we need the attrs member in the iova_attrs structure? The > "attrs" really are flags passed to the mapping routines that are > per-operation and not persistent, so I'd expect them to be passed > per-call and not stored in a structure. It is left-over from my not-send version where I added new attribute to indicate that dma_alloc_iova() can't support SWIOTLB to avoid dev_use_swiotlb() mess. I will remove it. > > I'd also expect that the use_iova field to be in the mapping state > and not separately provided by the driver. > > For nvme specific data structures I would have expected a dma_add/ > len pair in struct iod_dma_map, maybe even using a common type. > > Also the data structure split seems odd - I'd expect the actual > mapping state and a small number (at least one) dma_addr/len pair > to be inside the nvme_iod structure, and then only do the dynamic > allocation if we need more of them because there are more segments > and we are not using the iommu. > > If we had a common data structure for the dma_addr/len pairs > dma_unlink_range could just take care of the unmap for the non-iommu > case as well, which would be neat. I'd also expect that > dma_free_iova would be covered by it. Internally Jason asked for the same thing, but I didn't want to produce asymmetric API where drivers have a call to dma_alloc_iova() but don't have a call to dma_free_iova(). However, now, it is 2 versus 1, so I will change it. > > I would have expected dma_link_range to return the dma_addr_t instead > of poking into the iova structure in the callers. > > In __nvme_rq_dma_map the <= PAGE_SIZE case is pointless. In the > existing code the reason for it is to avoid allocating and mapping the > sg_table, but that code is still left before we even get to this code. > > My suggestion above to only allocate the dma_addr/len pairs when there > is more than 1 or a few of it would allow to trivially implement that > suggestion using the normal API without having to keep that special > case and the dma_len parameter around. > > If this addes a version of dma_map_page_atttrs that directly took > the physical address as a prep patch the callers would not have to > bother with page pointer manipulations and just work on physical > addresses for both the iommu and no-iommu cases. It would also help > a little bit with the eventualy switch to store the physical address > instead of page+offset in the bio_vec. Talking about that, I've > been wanting to add a bvec_phys helper for to convert the > page_phys(bv.bv_page) + bv.bv_offset calculations. This is becoming > more urgent with more callers needing to that, I'll try to get it out > to Jens ASAP so that it can make the 6.11 merge window. > > Can we make dma_start_range / dma_end_range simple no-ops for the > non-iommu code to avoid boilerplate code in the callers to avoid > boilerplate code in the callers to deal with the two cases? Yes, sure. Thanks
