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diff --git a/Documentation/firmware-guide/acpi/dsd/graph.rst b/Documentation/firmware-guide/acpi/dsd/graph.rst new file mode 100644 index 0000000000..b9dbfc73ed --- /dev/null +++ b/Documentation/firmware-guide/acpi/dsd/graph.rst @@ -0,0 +1,173 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====== +Graphs +====== + +_DSD +==== + +_DSD (Device Specific Data) [dsd-guide] is a predefined ACPI device +configuration object that can be used to convey information on +hardware features which are not specifically covered by the ACPI +specification [acpi]. There are two _DSD extensions that are relevant +for graphs: property [dsd-guide] and hierarchical data extensions. The +property extension provides generic key-value pairs whereas the +hierarchical data extension supports nodes with references to other +nodes, forming a tree. The nodes in the tree may contain properties as +defined by the property extension. The two extensions together provide +a tree-like structure with zero or more properties (key-value pairs) +in each node of the tree. + +The data structure may be accessed at runtime by using the device_* +and fwnode_* functions defined in include/linux/fwnode.h . + +Fwnode represents a generic firmware node object. It is independent on +the firmware type. In ACPI, fwnodes are _DSD hierarchical data +extensions objects. A device's _DSD object is represented by an +fwnode. + +The data structure may be referenced to elsewhere in the ACPI tables +by using a hard reference to the device itself and an index to the +hierarchical data extension array on each depth. + + +Ports and endpoints +=================== + +The port and endpoint concepts are very similar to those in Devicetree +[devicetree, graph-bindings]. A port represents an interface in a device, and +an endpoint represents a connection to that interface. Also see [data-node-ref] +for generic data node references. + +All port nodes are located under the device's "_DSD" node in the hierarchical +data extension tree. The data extension related to each port node must begin +with "port" and must be followed by the "@" character and the number of the +port as its key. The target object it refers to should be called "PRTX", where +"X" is the number of the port. An example of such a package would be:: + + Package() { "port@4", "PRT4" } + +Further on, endpoints are located under the port nodes. The hierarchical +data extension key of the endpoint nodes must begin with +"endpoint" and must be followed by the "@" character and the number of the +endpoint. The object it refers to should be called "EPXY", where "X" is the +number of the port and "Y" is the number of the endpoint. An example of such a +package would be:: + + Package() { "endpoint@0", "EP40" } + +Each port node contains a property extension key "port", the value of which is +the number of the port. Each endpoint is similarly numbered with a property +extension key "reg", the value of which is the number of the endpoint. Port +numbers must be unique within a device and endpoint numbers must be unique +within a port. If a device object may only has a single port, then the number +of that port shall be zero. Similarly, if a port may only have a single +endpoint, the number of that endpoint shall be zero. + +The endpoint reference uses property extension with "remote-endpoint" property +name followed by a reference in the same package. Such references consist of +the remote device reference, the first package entry of the port data extension +reference under the device and finally the first package entry of the endpoint +data extension reference under the port. Individual references thus appear as:: + + Package() { device, "port@X", "endpoint@Y" } + +In the above example, "X" is the number of the port and "Y" is the number of +the endpoint. + +The references to endpoints must be always done both ways, to the +remote endpoint and back from the referred remote endpoint node. + +A simple example of this is show below:: + + Scope (\_SB.PCI0.I2C2) + { + Device (CAM0) + { + Name (_DSD, Package () { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "compatible", Package () { "nokia,smia" } }, + }, + ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), + Package () { + Package () { "port@0", "PRT0" }, + } + }) + Name (PRT0, Package() { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "reg", 0 }, + }, + ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), + Package () { + Package () { "endpoint@0", "EP00" }, + } + }) + Name (EP00, Package() { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "reg", 0 }, + Package () { "remote-endpoint", Package() { \_SB.PCI0.ISP, "port@4", "endpoint@0" } }, + } + }) + } + } + + Scope (\_SB.PCI0) + { + Device (ISP) + { + Name (_DSD, Package () { + ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), + Package () { + Package () { "port@4", "PRT4" }, + } + }) + + Name (PRT4, Package() { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "reg", 4 }, /* CSI-2 port number */ + }, + ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), + Package () { + Package () { "endpoint@0", "EP40" }, + } + }) + + Name (EP40, Package() { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "reg", 0 }, + Package () { "remote-endpoint", Package () { \_SB.PCI0.I2C2.CAM0, "port@0", "endpoint@0" } }, + } + }) + } + } + +Here, the port 0 of the "CAM0" device is connected to the port 4 of +the "ISP" device and vice versa. + + +References +========== + +[acpi] Advanced Configuration and Power Interface Specification. + https://uefi.org/specifications/ACPI/6.4/, referenced 2021-11-30. + +[data-node-ref] Documentation/firmware-guide/acpi/dsd/data-node-references.rst + +[devicetree] Devicetree. https://www.devicetree.org, referenced 2016-10-03. + +[dsd-guide] DSD Guide. + https://github.com/UEFI/DSD-Guide/blob/main/dsd-guide.adoc, referenced + 2021-11-30. + +[dsd-rules] _DSD Device Properties Usage Rules. + Documentation/firmware-guide/acpi/DSD-properties-rules.rst + +[graph-bindings] Common bindings for device graphs (Devicetree). + https://github.com/devicetree-org/dt-schema/blob/main/schemas/graph.yaml, + referenced 2021-11-30. |