On Mon, Apr 18, 2011 at 8:58 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Monday 18 April 2011, Tony Lindgren wrote: >> * Arnd Bergmann <arnd@xxxxxxxx> [110418 10:26]: >> > On Friday 15 April 2011, Russell King - ARM Linux wrote: >> > > On Thu, Apr 14, 2011 at 04:52:48PM -0500, Fernando Guzman Lugo wrote: >> > > > From: Ramesh Gupta <grgupta@xxxxxx> >> > > > >> > > > This patch is to flush the iommu page table entries from L1 and L2 >> > > > caches using dma_map_single. This also simplifies the implementation >> > > > by removing the functions flush_iopgd_range/flush_iopte_range. >> > > >> > > No. This usage is just wrong. If you're going to use the DMA API then >> > > unmap it, otherwise the DMA API debugging will go awol. >> > >> > >> > It's also completely upside-down: The iommu support should provide interfaces >> > using the dma-mapping API, not use that API to provide a machine specific >> > version of the generic interface. >> > >> > As far as I can tell, nothing actually uses these drivers, maybe we should just >> > remove them before we get any code in the mainline kernel that depends on it. >> >> There is drivers/media/video/omap3isp/isp.c. > > Ah, I didn't see that, was looking at an older version. > >> But if we now have a generic replacement for this code we should start >> using it. > > To give some background: > > Historically, the dma-mapping API has been used for all IOMMUs on > architectures that need it. This interface is rather flexible, > but ARM currently only uses it for managing static mappings. > One thing that it cannot do is mapping memory to an arbitrary > (driver-chosen) bus address. The generic iommu API was added in order > to do that, and is mostly used for virtual machines with KVM. > > The MSM platform in ARM also added support for the generic iommu > API, and now the exynos4 is gaining support for it as well. You can find a exynos4 patches. http://comments.gmane.org/gmane.linux.drivers.video-input-infrastructure/31613 > > One missing piece is still a way for a platform to provide both > the iommu and the dma-mapping API in a unified driver. Right now, > you have to export both interface for a generic solution. Actually MSM and we (Michal, Marek) tried to merge the generic IOMMU implementation into mm, but MM did't accept it. So now it's implemented at each SoCs. I think it's good chance to make a generic IOMMU feature for ARM consolidation. > > On ARM, we don't yet use include/asm-generic/dma-mapping-common.h, > which allows overriding the dma-mapping API per device. This would > have to change if you want to export the IOMMU functionality using > the dma-mapping API, but that would also allow abstracting the > various ways we currently have (dmabounce, swiotlb, linear map, > custom __arch_page_to_dma, iommu, coherent or noncoherent DMA) > in a nicer way per device. Before this idea, can you review our implementation at above URL? Thank you, Kyungmin Park > > Arnd > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > -- 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
