On Fri, Jun 3, 2011 at 3:12 AM, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > Hi Russell, > > On Wednesday 01 June 2011 16:03:06 Russell King - ARM Linux wrote: >> On Wed, Jun 01, 2011 at 03:50:50PM +0200, Laurent Pinchart wrote: >> > In the specific iovmm case, the driver uses the sglist API to build a >> > list of page-size sg entries, and then process it in software. Is that >> > considered as an abuse of the sglist API, or valid usage ? >> > >> > Anyway, sglist chaining is not needed by iovmm. As iovmm just walks the >> > sglist manually, it's easier to allocate it in one go rather than using >> > sglist chaining. This of course doesn't make your patch unneeded or >> > wrong. >> >> Well, there's a two issues here: >> 1. Should iovmm use sg_phys(sg) with sg_dma_len(sg) ? >> Â ÂProbably not, because a scatterlist before DMA API mapping is defined >> Â Âby sg_page(sg), sg->offset, sg->length and has N entries. ÂAfter DMA >> Â ÂAPI mapping (n = dma_map_sg(dev, sg, N, dir)), it has n entries where >> Â Ân <= N, and the DMA address/lengths are sg_dma_address(sg) and >> Â Âsg_dma_len(sg). ÂBoth these are undefined for unmapped scatterlists. >> >> Â ÂGetting this wrong means breakage when CONFIG_NEED_SG_DMA_LENGTH is >> Â Âenabled. > > iovmm abuses the sglist API, there's no doubt on that. It will break when > CONFIG_NEED_SG_DMA_LENGTH is enabled. iovmm should probably not use the sglist > API, and it should probably not even exist in the first place. I know that TI > is working on moving the OMAP-specific iommu/iovmm implementation to the > generic IOMMU API, but that will take time. In the meantime, I'd like to fix > iovmm to avoid the userspace-triggerable BUG_ON(). This would also allow the tidspbridge driver to use iommu. -- Felipe Contreras -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
