On Wed, Jul 30, 2014 at 07:18:42PM +0100, Mark Rutland wrote: [...] > > >> + > > >> +Multiple-master IOMMU with configurable DMA window: > > >> +--------------------------------------------------- > > >> + > > >> + / { > > >> + #address-cells = <1>; > > >> + #size-cells = <1>; > > >> + > > >> + iommu { > > >> + /* master ID, address and length of DMA window */ > > >> + #iommu-cells = <4>; > > >> + }; > > >> + > > >> + master { > > >> + /* master ID 42, 4 GiB DMA window starting at 0 */ > > >> + iommus = <&/iommu 42 0 0x1 0x0>; > > > > > > Is this that window is from the POV of the master, i.e. the master can > > > address 0x0 to 0xffffffff when generating transactions, and these get > > > translated somehow? > > > > > > Or is this the physical addresses to allocate to the master? > > > > It needs to be clarified in the documentation, but as far as I know it > > is the DMA address space that is used. > > Ok. So that's pre-translation, from the POV of the master? Correct. It represents the window of the IOMMU's addressable I/O virtual address space that should be assigned to this particular master. > If we don't have that knowledge about the master already (e.g. based on > the compatible string), surely we always need that information in a > given iommu-specifier format? Otherwise certain iommus won't be able to > handle masters with limited addressing only due to limitations of their > binding. This is only used for what's often called a windowed IOMMU. Many IOMMUs (non-windowed) typically allow only a complete address space to be assigned to a master without additional control over subregions. So this is really a property/capability of the IOMMU rather than the masters themselves. There are already other means to respect the addressing limitations of masters. We typcially use a device's DMA mask for this, and it's natural to reuse that for I/O virtual addresses since they will in fact take the place of physical addresses for the master when translation is enabled. Thierry
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