Hi Joerg,
On Tue, 18 Sep 2012 14:49:18 +0200 Joerg Roedel joerg.roedel@amd.com wrote:
On Wed, Aug 29, 2012 at 09:55:30AM +0300, Hiroshi Doyu wrote:
The following APIs are needed for us to support the legacy Tegra memory manager for devices("NvMap") with *DMA mapping API*.
Maybe I am not understanding the need completly. Can you elaborate on why this is needed for legacy Tegra?
Actually not for legacy but it's necessary to replace homebrewed in-kernel API(not upstreamed) with the standard ones. The homebrewed in-kernel API has been used for the abvoe nvmap as its backend. The homebrewed ones are being replaced with the standard ones, IOMMU-API, DMA-API and dma-buf, mainly for transition purpose. I found that some missing features in DMA-API for that. I posted since other SoCs may have the similiar requirements, (1) To specify IOVA address at allocation, and (2) To have IOVA allocation and mapping separately.
New API:
->iova_alloc(): To allocate IOVA area. ->iova_alloc_at(): To allocate IOVA area at specific address. ->iova_free(): To free IOVA area.
->map_page_at(): To map page at specific IOVA.
This sounds like a layering violation. The situation today is as follows:
DMA-API : Handle DMA-addresses including an address allocator IOMMU-API : Full control over DMA address space, no address allocator
So what you want to do add to the DMA-API is already part of the IOMMU-API.
Here is my suggestion what you can do instead of extending the DMA-API. You can use the IOMMU-API to initialize the device address space with any mappings at the IOVAs you need the mappings. In the end you allocate another free range in the device address space and use that to satisfy DMA-API allocations. Any reason why that could not work?
I guess that it would work. Originally I thought that using DMA-API and IOMMU-API together in driver might be kind of layering violation since IOMMU-API itself is used in DMA-API. Only DMA-API used in driver might be cleaner. Considering that DMA API traditionally handling *anonymous* {bus,iova} address only, introducing the concept of specific address in DMA API may not be so encouraged, though.
It would be nice to listen how other SoCs have solved similar needs.