1 .. SPDX-License-Identifier: GPL-2.0
2 .. include:: <isonum.txt>
3
4 ========================================
5 Describing and referring to LEDs in ACPI
6 ========================================
7
8 Individual LEDs are described by hierarchical
9 device node, the LED driver chip. The "reg" pr
10 tells the numerical ID of each individual LED
11 connected. [leds] The hierarchical data nodes
12 number of the LED output.
13
14 Referring to LEDs in Device tree is documented
15 "flash-leds" property documentation. In short,
16 using phandles.
17
18 While Device tree allows referring to any node
19 ACPI references are limited to device nodes on
20 the same mechanism on ACPI is not possible. A
21 ACPI nodes is documented in [data-node-ref].
22
23 ACPI allows (as does DT) using integer argumen
24 combination of the LED driver device reference
25 referring to the "reg" property of the relevan
26 individual LEDs. The value of the "reg" proper
27 firmware and software, it uniquely identifies
28
29 Under the LED driver device, The first hierarc
30 entry shall contain the string "led@" followed
31 followed by the referred object name. That obj
32 by the number of the LED.
33
34 Example
35 =======
36
37 An ASL example of a camera sensor device and a
38 show below. Objects not relevant for LEDs or t
39 omitted. ::
40
41 Device (LED)
42 {
43 Name (_DSD, Package () {
44 ToUUID("dbb8e3e6-5886-
45 Package () {
46 Package () { "
47 Package () { "
48 }
49 })
50 Name (LED0, Package () {
51 ToUUID("daffd814-6eba-
52 Package () {
53 Package () { "
54 Package () { "
55 Package () { "
56 Package () { "
57 Package () { "
58 }
59 })
60 Name (LED1, Package () {
61 ToUUID("daffd814-6eba-
62 Package () {
63 Package () { "
64 Package () { "
65 Package () { "
66 }
67 })
68 }
69
70 Device (SEN)
71 {
72 Name (_DSD, Package () {
73 ToUUID("daffd814-6eba-
74 Package () {
75 Package () {
76 "flash
77 Packag
78 }
79 }
80 })
81 }
82
83 where
84 ::
85
86 LED LED driver device
87 LED0 First LED
88 LED1 Second LED
89 SEN Camera sensor device (or anoth
90
91 References
92 ==========
93
94 [acpi] Advanced Configuration and Power Interf
95 https://uefi.org/specifications/ACPI/6.4/,
96
97 [data-node-ref] Documentation/firmware-guide/a
98
99 [devicetree] Devicetree. https://www.devicetre
100
101 [dsd-guide] DSD Guide.
102 https://github.com/UEFI/DSD-Guide/blob/mai
103 2021-11-30.
104
105 [leds] Documentation/devicetree/bindings/leds/
106
107 [video-interfaces] Documentation/devicetree/bi
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