112 lines
3.5 KiB
ReStructuredText
112 lines
3.5 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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.. include:: <isonum.txt>
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========================================
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Describing and referring to LEDs in ACPI
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========================================
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Individual LEDs are described by hierarchical data extension [6] nodes under the
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device node, the LED driver chip. The "reg" property in the LED specific nodes
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tells the numerical ID of each individual LED output to which the LEDs are
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connected. [3] The hierarchical data nodes are named "led@X", where X is the
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number of the LED output.
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Referring to LEDs in Device tree is documented in [4], in "flash-leds" property
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documentation. In short, LEDs are directly referred to by using phandles.
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While Device tree allows referring to any node in the tree[1], in ACPI
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references are limited to device nodes only [2]. For this reason using the same
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mechanism on ACPI is not possible. A mechanism to refer to non-device ACPI nodes
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is documented in [7].
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ACPI allows (as does DT) using integer arguments after the reference. A
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combination of the LED driver device reference and an integer argument,
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referring to the "reg" property of the relevant LED, is used to identify
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individual LEDs. The value of the "reg" property is a contract between the
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firmware and software, it uniquely identifies the LED driver outputs.
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Under the LED driver device, The first hierarchical data extension package list
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entry shall contain the string "led@" followed by the number of the LED,
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followed by the referred object name. That object shall be named "LED" followed
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by the number of the LED.
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Example
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=======
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An ASL example of a camera sensor device and a LED driver device for two LEDs is
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show below. Objects not relevant for LEDs or the references to them have been
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omitted. ::
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Device (LED)
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{
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Name (_DSD, Package () {
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ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
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Package () {
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Package () { "led@0", LED0 },
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Package () { "led@1", LED1 },
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}
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})
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Name (LED0, Package () {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "reg", 0 },
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Package () { "flash-max-microamp", 1000000 },
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Package () { "flash-timeout-us", 200000 },
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Package () { "led-max-microamp", 100000 },
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Package () { "label", "white:flash" },
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}
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})
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Name (LED1, Package () {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "reg", 1 },
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Package () { "led-max-microamp", 10000 },
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Package () { "label", "red:indicator" },
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}
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})
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}
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Device (SEN)
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{
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Name (_DSD, Package () {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () {
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"flash-leds",
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Package () { ^LED, "led@0", ^LED, "led@1" },
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}
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}
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})
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}
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where
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::
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LED LED driver device
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LED0 First LED
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LED1 Second LED
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SEN Camera sensor device (or another device the LED is related to)
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References
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==========
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[1] Device tree. https://www.devicetree.org, referenced 2019-02-21.
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[2] Advanced Configuration and Power Interface Specification.
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https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf,
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referenced 2019-02-21.
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[3] Documentation/devicetree/bindings/leds/common.txt
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[4] Documentation/devicetree/bindings/media/video-interfaces.txt
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[5] Device Properties UUID For _DSD.
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https://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf,
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referenced 2019-02-21.
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[6] Hierarchical Data Extension UUID For _DSD.
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https://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.1.pdf,
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referenced 2019-02-21.
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[7] Documentation/firmware-guide/acpi/dsd/data-node-references.rst
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