[PATCH 15/15] ACPI / DSD: Document references, ports and endpoints

Sakari Ailus
2017-01-27T16:11:27Z

Document the use of references into the hierarchical data extension
structure, as well as the use of port and endpoint concepts that are very
similar to those in Devicetree.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
Documentation/acpi/dsd/graph.txt | 166 +++++++++++++++++++++++++++++++++++++++
1 file changed, 166 insertions(+)
create mode 100644 Documentation/acpi/dsd/graph.txt

diff --git a/Documentation/acpi/dsd/graph.txt b/Documentation/acpi/dsd/graph.txt
new file mode 100644
index 0000000..928cc07
--- /dev/null
+++ b/Documentation/acpi/dsd/graph.txt
@@ -0,0 +1,166 @@
+Graphs
+
+
+_DSD
+----
+
+_DSD (Device Specific Data) [7] 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 [1][6]. There are two _DSD extensions that are relevant
+for graphs: property [4] and hierarchical data extensions [5]. 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
+[3]. The port represent represent interface in a device, and an
+endpoint represents a connection to that interface.
+
+All port nodes are located under the device's "_DSD" node in
+hierarchical data extension tree. The first package list entry of the
+hierarchical data extension related to each port node must begin with
+"port" string and must be followed by the number of the port.
+
+Further on, endpoints are located under the individual port nodes. The
+first hierarchical data extension package list entry of the endpoint
+nodes must begin with "endpoint" and must be followed by the number
+of the endpoint.
+
+Each port node contains a property extension key "port", the value of
+which is the number of the port node. Similarly, each endpoint node
+must contain "endpoint" property which is the number of the endpoint
+node.
+
+The endpoint reference uses property extension with "remote-endpoint"
+property name followed by a reference in the same package. Such
+references consist of the name of the device, index of the port node
+and finally the index of the endpoint node. These indices are indeed
+indices to the referred port and endpoint arrays, not the numbers of
+the ports or the endpoints that are related to numbering of actual
+hardware interfaces in the respective hardware. Individual references
+thus appear as:
+
+ Package() { device, port_node_index, endpoint_node_index }
+
+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 () { "port0", "PRT0" },
+ }
+ })
+ Name (PRT0, Package() {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () { "port", 0 },
+ },
+ ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ Package () {
+ Package () { "endpoint0", "EP0" },
+ }
+ })
+ Name (EP0, Package() {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () { "endpoint", 0 },
+ Package () { "remote-endpoint", Package() { \_SB.PCI0.ISP, 0, 0 } },
+ }
+ })
+ }
+ }
+
+ Scope (\_SB.PCI0)
+ {
+ Device (ISP)
+ {
+ Name (_DSD, Package () {
+ ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ Package () {
+ Package () { "port4", "PRT4" },
+ }
+ })
+
+ Name (PRT4, Package() {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () { "port", 4 }, /* CSI-2 port number */
+ },
+ ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ Package () {
+ Package () { "endpoint0", "EP0" },
+ }
+ })
+
+ Name (EP0, Package() {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () { "endpoint", 0 },
+ Package () { "remote-endpoint", Package () { \_SB.PCI0.I2C2.CAM0, 0, 0 } },
+ }
+ })
+ }
+ }
+
+Here, the port 0 of the "CAM0" device is connected to the port 4 of
+the "ISP" device. Note that the port index in the reference is still
+0, as it refers to an entry in the table and not the port node number
+itself.
+
+
+References
+----------
+
+[1] _DSD (Device Specific Data) Implementation Guide.
+ <URL:http://www.uefi.org/sites/default/files/resources/_DSD-implementation-guide-toplevel-1_1.htm>,
+ referenced 2016-10-03.
+
+[2] Devicetree. <URL:http://www.devicetree.org>, referenced 2016-10-03.
+
+[3] Documentation/devicetree/bindings/graph.txt
+
+[4] Device Properties UUID For _DSD.
+ <URL:http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf>,
+ referenced 2016-10-04.
+
+[5] Hierarchical Data Extension UUID For _DSD.
+ <URL:http://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.pdf>,
+ referenced 2016-10-04.
+
+[6] Advanced Configuration and Power Interface Specification.
+ <URL:http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf>,
+ referenced 2016-10-04.
+
+[7] _DSD Device Properties Usage Rules.
+ Documentation/acpi/DSD-properties-rules.txt
--
2.7.4