[nrf fromtree] dts: bindings: clock: nrf53-hfxo: add startup-time-us prop

Add the clock startup time property to the nrf53 series HFXO binding.

Note that the values added to the soc .dtsi files are worst case
defaults, which will be replaced with optimal values at board level
in the future, as they depend on the specific crystal in use.

Signed-off-by: Bjarki Arge Andreasen <[email protected]>
(cherry picked from commit b9fdef6)
Signed-off-by: Rafał Kuźnia <[email protected]>

Author: bjarki-andreasen

dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi

@@ -26,6 +26,7 @@ oscillators: clock-controller@4000 {
 		compatible = "nordic,nrf53-hfxo";
 		#clock-cells = <0>;
 		clock-frequency = <DT_FREQ_M(32)>;
+		startup-time-us = <1400>;
 	};
 };
 

dts/bindings/clock/nordic,nrf53-hfxo.yaml

@@ -11,6 +11,20 @@ properties:
   clock-frequency:
     const: 32000000
 
+  startup-time-us:
+    type: int
+    required: true
+    description: |
+      Startup time in microseconds.
+
+      The value can be obtained by first measuring the time between
+      TASKS_HFCLKSTART and EVENTS_HFCLKSTARTED. Then multiply
+      the value by 2 to account for temperature and supply variations.
+
+      Note that the startup time will be longer usual on the first
+      power-up and as such should not be used to determine
+      startup-time-us.
+
   load-capacitors:
     type: string
     enum: