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Diffstat (limited to 'Documentation/acpi/dsd/leds.txt')
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diff --git a/Documentation/acpi/dsd/leds.txt b/Documentation/acpi/dsd/leds.txt new file mode 100644 index 000000000000..81a63af42ed2 --- /dev/null +++ b/Documentation/acpi/dsd/leds.txt @@ -0,0 +1,99 @@ +Describing and referring to LEDs in ACPI + +Individual LEDs are described by hierarchical data extension [6] nodes under the +device node, the LED driver chip. The "reg" property in the LED specific nodes +tells the numerical ID of each individual LED output to which the LEDs are +connected. [3] The hierarchical data nodes are named "led@X", where X is the +number of the LED output. + +Referring to LEDs in Device tree is documented in [4], in "flash-leds" property +documentation. In short, LEDs are directly referred to by using phandles. + +While Device tree allows referring to any node in the tree[1], in ACPI +references are limited to device nodes only [2]. For this reason using the same +mechanism on ACPI is not possible. A mechanism to refer to non-device ACPI nodes +is documented in [7]. + +ACPI allows (as does DT) using integer arguments after the reference. A +combination of the LED driver device reference and an integer argument, +referring to the "reg" property of the relevant LED, is used to identify +individual LEDs. The value of the "reg" property is a contract between the +firmware and software, it uniquely identifies the LED driver outputs. + +Under the LED driver device, The first hierarchical data extension package list +entry shall contain the string "led@" followed by the number of the LED, +followed by the referred object name. That object shall be named "LED" followed +by the number of the LED. + +An ASL example of a camera sensor device and a LED driver device for two LEDs. +Objects not relevant for LEDs or the references to them have been omitted. + + Device (LED) + { + Name (_DSD, Package () { + ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"), + Package () { + Package () { "led@0", LED0 }, + Package () { "led@1", LED1 }, + } + }) + Name (LED0, Package () { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "reg", 0 }, + Package () { "flash-max-microamp", 1000000 }, + Package () { "flash-timeout-us", 200000 }, + Package () { "led-max-microamp", 100000 }, + Package () { "label", "white:flash" }, + } + }) + Name (LED1, Package () { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { "reg", 1 }, + Package () { "led-max-microamp", 10000 }, + Package () { "label", "red:indicator" }, + } + }) + } + + Device (SEN) + { + Name (_DSD, Package () { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package () { + "flash-leds", + Package () { ^LED, "led@0", ^LED, "led@1" }, + } + } + }) + } + +where + + LED LED driver device + LED0 First LED + LED1 Second LED + SEN Camera sensor device (or another device the LED is + related to) + +[1] Device tree. <URL:http://www.devicetree.org>, referenced 2019-02-21. + +[2] Advanced Configuration and Power Interface Specification. + <URL:https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf>, + referenced 2019-02-21. + +[3] Documentation/devicetree/bindings/leds/common.txt + +[4] Documentation/devicetree/bindings/media/video-interfaces.txt + +[5] Device Properties UUID For _DSD. + <URL:http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf>, + referenced 2019-02-21. + +[6] Hierarchical Data Extension UUID For _DSD. + <URL:http://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.1.pdf>, + referenced 2019-02-21. + +[7] Documentation/acpi/dsd/data-node-reference.txt |