ACPI: Document how to refer to LEDs from remote nodes

[sfrench/cifs-2.6.git] / Documentation / acpi / dsd / leds.txt

diff --git a/Documentation/acpi/dsd/leds.txt b/Documentation/acpi/dsd/leds.txt
new file mode 100644 (file)
index 0000000..81a63af
--- /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