Document referring to LEDs from remote device nodes, such as from camera
sensors.
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
Documentation/acpi/dsd/leds.txt | 92 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 92 insertions(+)
create mode 100644 Documentation/acpi/dsd/leds.txt
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+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 "led" property in the
+LED specific nodes tells the numerical ID of each individual LED. The
+"led" property is used here in a similar fashion as the "reg" property
+in DT. [3]
+
+Referring to LEDs in Devicetree is documented in [4], in "flash-leds"
+property documentation. In short, LEDs are directly referred to by
+using phandles.
+
+While Devicetree 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.
+
+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 "led" property of the relevant LED, are
+use to individual LEDs. The value of the LED property is a contract
+between the firmware and software, it uniquely identifies the LED
+driver outputs.
+
+An ASL example of a camera sensor device and a LED driver device for
+two LEDs:
+
+ Device (LED)
+ {
+ Name ((_DSD), Package () {
+ ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ Package () {
+ Package () { "led0", "LED0" },
+ Package () { "led1", "LED1" },
+ }
+ })
+ Name ((LED0), Package () {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () { "led", 0 },
+ Package () { "flash-max-microamp", 1000000 },
+ Package () { "led-max-microamp", 100000 },
+ Package () { "label", "led:salama" },
+ }
+ })
+ Name ((LED1), Package () {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () { "led", 1 },
+ Package () { "led-max-microamp", 10000 },
+ Package () { "label", "led:huomiovalo" },
+ }
+ })
+ }
+
+ Device (SEN)
+ {
+ Name ((_DSD), Package () {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () {
+ "flash-leds",
+ Package () { \\LED, 0, \\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] Devicetree. <URL:http://www.devicetree.org>, referenced 2016-10-03.
+
+[2] Advanced Configuration and Power Interface Specification.
+ <URL:http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf>,
+ referenced 2016-10-04.
+
+[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 2016-10-04.
+
+[6] Hierarchical Data Extension UUID For _DSD.
+ <URL:http://www.uefi.org/sites/default/files/resources/_DSD-hierarchical-data-extension-UUID-v1.pdf>,
+ referenced 2016-10-04.
--
2.11.0
