On Monday 12 May 2014 12:29:16 Stephen Warren wrote: > On 05/12/2014 12:10 PM, Arnd Bergmann wrote: > > On Monday 12 May 2014 10:19:16 Stephen Warren wrote: > >> IIRC, the current Nouveau support for Tegra even makes use of that > >> feature, although I think that's a temporary thing that we're hoping to > >> get rid of once the Tegra support in Nouveau gets more mature. > > > > But the important point here is that you wouldn't use the dma-mapping > > API to manage this. First of all, the CPU is special anyway, but also > > if you do a device-to-device DMA into the GPU address space and that > > ends up being redirected to memory through the IOMMU, you still wouldn't > > manage the I/O page tables through the interfaces of the device doing the > > DMA, but through some private interface of the GPU. > > Why not? If something wants to DMA to a memory region, irrespective of > whether the GPU MMU (or any MMU) is in between those master transactions > and the RAM or not, surely the driver should always use the DMA mapping > API to set that up? Anything else just means using custom APIs, and > isn't the whole point of the DMA mapping API to provide a standard API > for that purpose? It sounds like an abuse of the hardware if you use the GPU's IOMMU to set up DMA for a random non-GPU DMA master. I'd prefer not to go there and instead use swiotlb. Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
