CC'ed Jens, James, and linux-scsi. On Thu, 27 Sep 2007 03:31:55 -0400 Jeff Garzik <jeff@xxxxxxxxxx> wrote: > FUJITA Tomonori wrote: > > Yeah, we could nicely handle lld's restrictions (especially with > > stacking devices). But iommu code needs only max_segment_size and > > seg_boundary_mask, right? If so, the first simple approach to add two > > values to device structure is not so bad, I think. > > (replying to slightly older email in the thread) > (added benh, since we've discussed this issue in the past) > > dumb question, what happened to seg_boundary_mask? I'll work on it too after finishing max_seg_size. > If you look at drivers/ata/libata-core.c:ata_fill_sg(), you will note > that we split s/g segments after DMA-mapping. Looking at libata LLDD's, > you will also note judicious use of ATA_DMA_BOUNDARY (0xffff). I know the workaround since I fixed libata's sg chaining patch. > It was drilled into my head by James and benh that I cannot rely on the > DMA boundary + block/scsi + dma_map_sg() to ensure that my S/G segments > never cross a 64K boundary, a legacy IDE requirement. Thus the > additional code in ata_fill_sg() to split S/G segments straddling 64K, > in addition to setting dma boundary to 0xffff. I think that the block layer can handle both max_segment_size and seg_boundary_mask properly (and SCSI-ml just uses the block layer). So if we fix iommu, then we can remove a workaround to fix sg lists in llds. > A key problem I was hoping would be solved with your work here was the > elimination of that post dma_map_sg() split. Yeah, that's my goal too. > If I understood James and Ben correctly, one of the key problems was > always in communicating libata's segment boundary needs to the IOMMU layers? > > Jeff > - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
