* Stephen Warren wrote: > On 04/06/2012 01:20 AM, Thierry Reding wrote: > > * Stephen Warren wrote: > >> I must admit I'm not at all familiar with the IOMMU APIs, but isn't the > >> IOMMU driver/subsystem itself what is managing all the allocations and > >> handing them out to clients? And client drivers do things like asking > >> for N pages of memory mapped into their aperture? If that is true, I'm > >> not sure what the purpose is of the intermediate device you propose. > >> Sorry for being somewhat clueless. > > > > That was my impression too at first. But it seems like all the IOMMU > > subsystem does is map individual pages. So you pass it a physical address of > > a page along with the IO virtual address to map it to. That's at least the > > way it is handled for Tegra 2 GART (and from a quick look also by the Tegra > > 3 > > SMMU). For the SMMU the situation may be different because it may not have a > > fixed aperture that needs to contain the IO virtual addresses, though I must > > admit I haven't looked at Tegra 3 in enough detail to judge this. > > > > So this intermediate device would be purely an allocator for the GART > > aperture and handle the actual mapping via the IOMMU. This would probably be > > really simple and is in fact now done in the DRM driver. The nice thing if > > this would be a separate device is that it would be easy to make it a child > > of the IOMMU and wouldn't be as counter-intuitive as making the DRM device > > the IOMMU's child. > > OK, I see. > > I'll defer to Hiroshi here; he's far more familiar with all this than I am. > > My only comment is that I'd be surprised to see any kind of memory > allocator represented as a driver (as opposed to a utility module) since > it's not really representing an actual hardware block.
I agree. In that case I don't see any other solution than to remove the requirement of the parent/child relationship from the GART driver. It seems like the SMMU driver doesn't have such a requirement so it should be fine. Thierry
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