On Thu, Jun 20, 2013 at 4:27 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Thursday 20 June 2013, Hiroshi Doyu wrote: >> Arnd Bergmann <arnd@xxxxxxxx> wrote @ Thu, 20 Jun 2013 12:13:13 +0200: >> >> > On Thursday 20 June 2013, Hiroshi Doyu wrote: >> > > > If devices allocate via dma-mapping API, physical mem allocation, iova >> > > > allocation and iommu mapping happens internally. >> > > > Devices may allocate physical memory using any allocator (say ION >> > > > including carveout area), use "iommu mapping" API which will do iova >> > > > allocation and iommu mapping. The prot flags could be useful in this >> > > > case as well - not sure whether we would need dma-attrs here. >> > > >> > > I haven't followed ION recently, but can't ION backed by DMA mapping >> > > API instead of using IOMMU API directly? >> > >> > For a GPU with an IOMMU, you typically want per-process IOMMU contexts, >> > which are only available when using the IOMMU API directly, as the >> > dma-mapping abstraction uses only one context for kernel space. >> >> Yes, we had some experiment for switching IOMMU context with DMA >> mapping API. We needed to add some new DMA mapping API, and didn't >> look so nice at that time. What do you think to introduce multiple >> context or switching context in dma-mapping abstruction? > > My feeling is that drivers with the need for multiple contexts > are better off using the iommu API, since that is what it was > made for. The dma-mapping abstraction really tries to hide the > bus address assignment, while users with multiple contexts typically > also want to control the bus addresses. > > Arnd ION is more of a physical memory allocator supporting buddy pages as well as memory reserved at boot-time. DMA type of heap is only one of the types of heap. For system heap, ION provides an sg_table which device will have to map it using iommu API to get dma_address for the device. Even for DMA type of heap, each device will have to map the pages to its own iommu as Arnd mentioned. - Nishanth Peethambaran -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
