Bluetooth: controller: Framework for new feature BT_CTLR_JIT_SCHEDULING

This option enables BT_TICKER_SLOT_AGNOSTIC which eliminates
priorities and collision resolving in the ticker.

Event scheduling states are stored in the lll_hdr, and event priority
is passed from LLL implementation, and runtime priority calculated.

LLL implementation decides whether to program radio, start preemption
timer, and/or queue prepare in the prepare pipeline.

Event arbitration is made possible via the common LLL, but not yet
implemented in Nordic LLL.

Signed-off-by: Morten Priess <mtpr@oticon.com>

subsys/bluetooth/controller/Kconfig.ll_sw_split

@@ -570,6 +570,15 @@ config BT_TICKER_SLOT_AGNOSTIC
 	  reservations and collision handling, and operates as a simple
 	  multi-instance programmable timer.
 
+config BT_CTLR_JIT_SCHEDULING
+	bool "Just-in-Time Scheduling"
+	select BT_TICKER_SLOT_AGNOSTIC
+	help
+	  This option enables the experimental 'Next Generation' scheduling
+	  feature, which eliminates priorities and collision resolving in the
+	  ticker, and instead relies on just-in-time ("lazy") resolution in
+	  the link layer.
+
 config BT_CTLR_USER_EXT
 	prompt "Enable proprietary extensions in Controller"
 	bool

subsys/bluetooth/controller/ll_sw/lll.h

@@ -160,12 +160,19 @@ struct ull_hdr {
 
 struct lll_hdr {
 	void *parent;
+#if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
+	uint8_t score;
+	uint8_t latency;
+#endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
 };
 
 struct lll_prepare_param {
 	uint32_t ticks_at_expire;
 	uint32_t remainder;
 	uint16_t lazy;
+#if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
+	int8_t  prio;
+#endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
 	uint8_t force;
 	void *param;
 };
@@ -379,8 +386,15 @@ static inline void lll_hdr_init(void *lll, void *parent)
 	struct lll_hdr *hdr = lll;
 
 	hdr->parent = parent;
+
+#if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
+	hdr->score = 0U;
+	hdr->latency = 0U;
+#endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
 }
 
+void lll_done_score(void *param, uint8_t too_late, uint8_t aborted);
+
 int lll_init(void);
 int lll_reset(void);
 void lll_resume(void *param);

subsys/bluetooth/controller/ll_sw/lll_common.c

@@ -41,7 +41,27 @@ int lll_prepare(lll_is_abort_cb_t is_abort_cb, lll_abort_cb_t abort_cb,
 		lll_prepare_cb_t prepare_cb, int8_t event_prio,
 		struct lll_prepare_param *prepare_param)
 {
-	/* TODO: Calculate priority */
+#if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
+	int prio = event_prio;
+	struct lll_hdr *hdr = prepare_param->param;
+
+	/* Establish priority based on:
+	 * 1. Event priority passed to function
+	 * 2. Force flag => priority = -127
+	 * 3. Score (events terminated- and too late)
+	 * 4. Latency (skipped- and programmed latency)
+	 * 5. Critical priority is immutable (-128)
+	 */
+	if (prio > -128) {
+		if (prepare_param->force) {
+			prio = -127;
+		} else {
+			prio = MAX(-127, prio - hdr->score - hdr->latency);
+		}
+	}
+
+	prepare_param->prio = prio;
+#endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
 
 	return lll_prepare_resolve(is_abort_cb, abort_cb, prepare_cb,
 				   prepare_param, 0, 0);
@@ -58,3 +78,21 @@ void lll_resume(void *param)
 				  next->is_resume, 1);
 	LL_ASSERT(!ret || ret == -EINPROGRESS);
 }
+
+#if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
+void lll_done_score(void *param, uint8_t too_late, uint8_t aborted)
+{
+	struct lll_hdr *hdr = param;
+
+	if (!hdr) {
+		return;
+	}
+
+	if (!too_late && !aborted) {
+		hdr->score  = 0;
+		hdr->latency = 0;
+	} else {
+		hdr->score++;
+	}
+}
+#endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */

subsys/bluetooth/controller/ll_sw/nordic/lll/lll.c

@@ -344,6 +344,10 @@ int lll_done(void *param)
 	ull_prepare_dequeue(TICKER_USER_ID_LLL);
 #endif /* !CONFIG_BT_CTLR_LOW_LAT_ULL_DONE */
 
+#if defined(CONFIG_BT_CTLR_JIT_SCHEDULING)
+	lll_done_score(param, 0, 0); /* TODO */
+#endif /* CONFIG_BT_CTLR_JIT_SCHEDULING */
+
 	/* Let ULL know about LLL event done */
 	evdone = ull_event_done(ull);
 	LL_ASSERT(evdone);