Bluetooth: controller: Fix ULL_HIGH priority to be lower than LLL

Fix the default ULL_HIGH execution priority to be lower than
LLL execution priority to reduce Radio ISR service latency.

Also, default to Zero Latency IRQ for Radio ISR if enabled
in the kernel.

Fixes #29994.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

subsys/bluetooth/controller/Kconfig.ll_sw_split

@@ -211,6 +211,7 @@ config BT_CTLR_SCAN_ENABLE_STRICT
 config BT_CTLR_ZLI
 	bool "Use Zero Latency IRQs"
 	depends on ZERO_LATENCY_IRQS
+	default y
 	help
 	  Enable support for use of Zero Latency IRQ feature. Note, applications
 	  shall not use Zero Latency IRQ themselves when this option is selected,
@@ -273,7 +274,7 @@ config BT_CTLR_SCHED_ADVANCED
 	  leading to skipped events amongst active roles.
 
 config BT_CTLR_LLL_PRIO
-	int "Lower Link Layer (Radio) IRQ priority"
+	int "Lower Link Layer (Radio) IRQ priority" if !BT_CTLR_ZLI
 	range 0 3 if SOC_SERIES_NRF51X
 	range 0 6 if (SOC_SERIES_NRF52X || SOC_SERIES_NRF53X)
 	default 0
@@ -284,7 +285,8 @@ config BT_CTLR_ULL_HIGH_PRIO
 	int "Upper Link Layer High IRQ priority"
 	range BT_CTLR_LLL_PRIO 3 if SOC_SERIES_NRF51X
 	range BT_CTLR_LLL_PRIO 6 if (SOC_SERIES_NRF52X || SOC_SERIES_NRF53X)
-	default BT_CTLR_LLL_PRIO
+	default BT_CTLR_LLL_PRIO if (BT_CTLR_ZLI || BT_CTLR_LOW_LAT_ULL)
+	default 1
 	help
 	  The interrupt priority for Ticker's Worker IRQ and Upper Link Layer
 	  higher priority functions.