Update key layout docs to include `key usage` syntax
Change-Id: If3cdd4dfd889b9e5ceebf4582db6a3775ab43355
diff --git a/src/tech/input/key-layout-files.md b/src/tech/input/key-layout-files.md
index 9a2760d..9f3088d 100644
--- a/src/tech/input/key-layout-files.md
+++ b/src/tech/input/key-layout-files.md
@@ -65,11 +65,16 @@
### Key Declarations ###
Key declarations each consist of the keyword `key` followed by a Linux key code
-number, an Android key code name, and optional set of whitespace delimited policy flags.
+number and an Android key code name, or the keyword `usage` followed by a HID
+usage and an Android key code name. The HID usage is represented as a 32-bit
+integer, where the high 16-bits represent the HID usage page and the low
+16-bits represent the HID usage ID. Either of these declarations can then be
+followed by an optional set of whitespace delimited policy flags.
key 1 ESCAPE
key 114 VOLUME_DOWN WAKE
key 16 Q VIRTUAL WAKE
+ key usage 0x0c006F BRIGHTNESS_UP
The following policy flags are recognized:
