1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
4 ========================================
5 Describing and referring to LEDs in ACPI
6 ========================================
8 Individual LEDs are described by hierarchical data extension [6] nodes under the
9 device node, the LED driver chip. The "reg" property in the LED specific nodes
10 tells the numerical ID of each individual LED output to which the LEDs are
11 connected. [3] The hierarchical data nodes are named "led@X", where X is the
12 number of the LED output.
14 Referring to LEDs in Device tree is documented in [4], in "flash-leds" property
15 documentation. In short, LEDs are directly referred to by using phandles.
17 While Device tree allows referring to any node in the tree[1], in ACPI
18 references are limited to device nodes only [2]. For this reason using the same
19 mechanism on ACPI is not possible. A mechanism to refer to non-device ACPI nodes
22 ACPI allows (as does DT) using integer arguments after the reference. A
23 combination of the LED driver device reference and an integer argument,
24 referring to the "reg" property of the relevant LED, is used to identify
25 individual LEDs. The value of the "reg" property is a contract between the
26 firmware and software, it uniquely identifies the LED driver outputs.
28 Under the LED driver device, The first hierarchical data extension package list
29 entry shall contain the string "led@" followed by the number of the LED,
30 followed by the referred object name. That object shall be named "LED" followed
31 by the number of the LED.
36 An ASL example of a camera sensor device and a LED driver device for two LEDs is
37 show below. Objects not relevant for LEDs or the references to them have been
42 Name (_DSD, Package () {
43 ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
45 Package () { "led@0", LED0 },
46 Package () { "led@1", LED1 },
49 Name (LED0, Package () {
50 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
52 Package () { "reg", 0 },
53 Package () { "flash-max-microamp", 1000000 },
54 Package () { "flash-timeout-us", 200000 },
55 Package () { "led-max-microamp", 100000 },
56 Package () { "label", "white:flash" },
59 Name (LED1, Package () {
60 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
62 Package () { "reg", 1 },
63 Package () { "led-max-microamp", 10000 },
64 Package () { "label", "red:indicator" },
71 Name (_DSD, Package () {
72 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
76 Package () { ^LED, "led@0", ^LED, "led@1" },
88 SEN Camera sensor device (or another device the LED is related to)
93 [1] Device tree. <URL:https://www.devicetree.org>, referenced 2019-02-21.
95 [2] Advanced Configuration and Power Interface Specification.
96 <URL:https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf>,
97 referenced 2019-02-21.
99 [3] Documentation/devicetree/bindings/leds/common.txt
101 [4] Documentation/devicetree/bindings/media/video-interfaces.txt
103 [5] Device Properties UUID For _DSD.
104 <URL:https://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf>,
105 referenced 2019-02-21.
107 [6] Hierarchical Data Extension UUID For _DSD.
108 <URL:https://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.1.pdf>,
109 referenced 2019-02-21.
111 [7] Documentation/firmware-guide/acpi/dsd/data-node-references.rst