Hello, On Friday, March 11, 2011 12:51 PM Arnd Bergmann wrote: > On Friday 11 March 2011, Marek Szyprowski wrote: > > > > We followed the style of iommu API for other mainline ARM platforms (both OMAP and MSM > > also have custom API for their iommu modules). I've briefly checked include/linux/iommu.h > > API and I've noticed that it has been designed mainly for KVM support. There is also > > include/linux/intel-iommu.h interface, but I it is very specific to intel gfx chips. > > The MSM code actually uses the generic iommu.h code, using register_iommu, so > the drivers can use the regular iommu_map. > > I believe the omap code predates the iommu API, and should really be changed > to use that. At least it was added before I started reviewing the code. > > The iommu API is not really meant to be KVM specific, it's just that the > in-tree users are basically limited to KVM at the moment. Another user that > is coming up soon is the vmio device driver that can be used to transparently > pass devices to user space. The idea behind the IOMMU API is that you can > map arbitrary bus addresses to physical memory addresses, but it does not > deal with allocating the bus addresses or providing buffer management such > as cache flushes. Yea, I've noticed this and this basically what we expect from iommu driver. However the iommu.h API requires a separate call to map each single memory page. This is quite ineffective approach and imho the API need to be extended to allow mapping of the arbitrary set of pages. > > Is there any example how include/linux/dma-mapping.h interface can be used for iommu > > mappings? > > The dma-mapping API is the normal interface that you should use for IOMMUs > that sit between DMA devices and kernel memory. The idea is that you > completely abstract the concept of an IOMMU so the device driver uses > the same code for talking to a device with an IOMMU and another device with > a linear mapping or an swiotlb bounce buffer. > > This means that the user of the dma-mapping API does not get to choose the > bus addresses, but instead you use the API to get a bus address for a > chunk of memory, and then you can pass that address to a device. > > See arch/powerpc/kernel/iommu.c and arch/x86/kernel/amd_iommu.c for common > examples of how this is implemented. The latter one actually implements > both the iommu_ops for iommu.h and dma_map_ops for dma-mapping.h. Thanks for your comments! We will check how is it suitable for our case. Best regards -- Marek Szyprowski Samsung Poland R&D Center -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
