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diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Documentation/devicetree/bindings/iommu/iommu.txt new file mode 100644 index 000000000000..5a8b4624defc --- /dev/null +++ b/Documentation/devicetree/bindings/iommu/iommu.txt @@ -0,0 +1,182 @@ +This document describes the generic device tree binding for IOMMUs and their +master(s). + + +IOMMU device node: +================== + +An IOMMU can provide the following services: + +* Remap address space to allow devices to access physical memory ranges that + they otherwise wouldn't be capable of accessing. + + Example: 32-bit DMA to 64-bit physical addresses + +* Implement scatter-gather at page level granularity so that the device does + not have to. + +* Provide system protection against "rogue" DMA by forcing all accesses to go + through the IOMMU and faulting when encountering accesses to unmapped + address regions. + +* Provide address space isolation between multiple contexts. + + Example: Virtualization + +Device nodes compatible with this binding represent hardware with some of the +above capabilities. + +IOMMUs can be single-master or multiple-master. Single-master IOMMU devices +typically have a fixed association to the master device, whereas multiple- +master IOMMU devices can translate accesses from more than one master. + +The device tree node of the IOMMU device's parent bus must contain a valid +"dma-ranges" property that describes how the physical address space of the +IOMMU maps to memory. An empty "dma-ranges" property means that there is a +1:1 mapping from IOMMU to memory. + +Required properties: +-------------------- +- #iommu-cells: The number of cells in an IOMMU specifier needed to encode an + address. + +The meaning of the IOMMU specifier is defined by the device tree binding of +the specific IOMMU. Below are a few examples of typical use-cases: + +- #iommu-cells = <0>: Single master IOMMU devices are not configurable and + therefore no additional information needs to be encoded in the specifier. + This may also apply to multiple master IOMMU devices that do not allow the + association of masters to be configured. Note that an IOMMU can by design + be multi-master yet only expose a single master in a given configuration. + In such cases the number of cells will usually be 1 as in the next case. +- #iommu-cells = <1>: Multiple master IOMMU devices may need to be configured + in order to enable translation for a given master. In such cases the single + address cell corresponds to the master device's ID. In some cases more than + one cell can be required to represent a single master ID. +- #iommu-cells = <4>: Some IOMMU devices allow the DMA window for masters to + be configured. The first cell of the address in this may contain the master + device's ID for example, while the second cell could contain the start of + the DMA window for the given device. The length of the DMA window is given + by the third and fourth cells. + +Note that these are merely examples and real-world use-cases may use different +definitions to represent their individual needs. Always refer to the specific +IOMMU binding for the exact meaning of the cells that make up the specifier. + + +IOMMU master node: +================== + +Devices that access memory through an IOMMU are called masters. A device can +have multiple master interfaces (to one or more IOMMU devices). + +Required properties: +-------------------- +- iommus: A list of phandle and IOMMU specifier pairs that describe the IOMMU + master interfaces of the device. One entry in the list describes one master + interface of the device. + +When an "iommus" property is specified in a device tree node, the IOMMU will +be used for address translation. If a "dma-ranges" property exists in the +device's parent node it will be ignored. An exception to this rule is if the +referenced IOMMU is disabled, in which case the "dma-ranges" property of the +parent shall take effect. Note that merely disabling a device tree node does +not guarantee that the IOMMU is really disabled since the hardware may not +have a means to turn off translation. But it is invalid in such cases to +disable the IOMMU's device tree node in the first place because it would +prevent any driver from properly setting up the translations. + + +Notes: +====== + +One possible extension to the above is to use an "iommus" property along with +a "dma-ranges" property in a bus device node (such as PCI host bridges). This +can be useful to describe how children on the bus relate to the IOMMU if they +are not explicitly listed in the device tree (e.g. PCI devices). However, the +requirements of that use-case haven't been fully determined yet. Implementing +this is therefore not recommended without further discussion and extension of +this binding. + + +Examples: +========= + +Single-master IOMMU: +-------------------- + + iommu { + #iommu-cells = <0>; + }; + + master { + iommus = <&{/iommu}>; + }; + +Multiple-master IOMMU with fixed associations: +---------------------------------------------- + + /* multiple-master IOMMU */ + iommu { + /* + * Masters are statically associated with this IOMMU and share + * the same address translations because the IOMMU does not + * have sufficient information to distinguish between masters. + * + * Consequently address translation is always on or off for + * all masters at any given point in time. + */ + #iommu-cells = <0>; + }; + + /* static association with IOMMU */ + master@1 { + reg = <1>; + iommus = <&{/iommu}>; + }; + + /* static association with IOMMU */ + master@2 { + reg = <2>; + iommus = <&{/iommu}>; + }; + +Multiple-master IOMMU: +---------------------- + + iommu { + /* the specifier represents the ID of the master */ + #iommu-cells = <1>; + }; + + master@1 { + /* device has master ID 42 in the IOMMU */ + iommus = <&{/iommu} 42>; + }; + + master@2 { + /* device has master IDs 23 and 24 in the IOMMU */ + iommus = <&{/iommu} 23>, <&{/iommu} 24>; + }; + +Multiple-master IOMMU with configurable DMA window: +--------------------------------------------------- + + / { + iommu { + /* + * One cell for the master ID and one cell for the + * address of the DMA window. The length of the DMA + * window is encoded in two cells. + * + * The DMA window is the range addressable by the + * master (i.e. the I/O virtual address space). + */ + #iommu-cells = <4>; + }; + + master { + /* master ID 42, 4 GiB DMA window starting at 0 */ + iommus = <&{/iommu} 42 0 0x1 0x0>; + }; + }; |