Bluetooth: Controller: Permit enabling already enabled advertising

Permit enabling already enabled advertising. Enabling
advertising when it is already enabled can cause the
random address to change, as specified in the Bluetooth
Specifications.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

subsys/bluetooth/controller/Kconfig.ll_sw_split

@@ -238,6 +238,13 @@ config BT_CTLR_SCAN_SYNC_ISO_SET
 	help
 	  Maximum supported broadcast isochronous groups (BIGs) sync sets.
 
+config BT_CTLR_ADV_ENABLE_STRICT
+	bool "Enforce Strict Advertising Enable/Disable"
+	depends on BT_BROADCASTER
+	help
+	  Enforce returning HCI Error Command Disallowed on enabling/disabling
+	  already enabled/disabled advertising.
+
 config BT_CTLR_SCAN_ENABLE_STRICT
 	bool "Enforce Strict Scan Enable/Disable"
 	depends on BT_OBSERVER

subsys/bluetooth/controller/ll_sw/ull_adv.c

@@ -76,6 +76,9 @@ static void conn_release(struct ll_adv_set *adv);
 #endif /* CONFIG_BT_PERIPHERAL */
 
 #if defined(CONFIG_BT_CTLR_ADV_EXT)
+static void adv_max_events_duration_set(struct ll_adv_set *adv,
+					uint16_t duration,
+					uint8_t max_ext_adv_evts);
 static void ticker_op_aux_stop_cb(uint32_t status, void *param);
 static void ticker_op_ext_stop_cb(uint32_t status, void *param);
 static void ext_disabled_cb(void *param);
@@ -734,6 +737,75 @@ uint8_t ll_adv_enable(uint8_t enable)
 
 	adv = is_disabled_get(handle);
 	if (!adv) {
+		/* Bluetooth Specification v5.0 Vol 2 Part E Section 7.8.9
+		 * Enabling advertising when it is already enabled can cause the
+		 * random address to change. As the current implementation does
+		 * does not update RPAs on every advertising enable, only on
+		 * `rpa_timeout_ms` timeout, we are not going to implement the
+		 * "can cause the random address to change" for legacy
+		 * advertisements.
+		 */
+
+		/* If HCI LE Set Extended Advertising Enable command is sent
+		 * again for an advertising set while that set is enabled, the
+		 * timer used for duration and the number of events counter are
+		 * reset and any change to the random address shall take effect.
+		 */
+		if (!IS_ENABLED(CONFIG_BT_CTLR_ADV_ENABLE_STRICT) ||
+		    IS_ENABLED(CONFIG_BT_CTLR_ADV_EXT)) {
+#if defined(CONFIG_BT_CTLR_ADV_EXT)
+			if (ll_adv_cmds_is_ext()) {
+				enum node_rx_type volatile *type;
+
+				adv = ull_adv_is_enabled_get(handle);
+				if (!adv) {
+					/* This should not be happening as
+					 * is_disabled_get failed.
+					 */
+					return BT_HCI_ERR_CMD_DISALLOWED;
+				}
+
+				if (!adv->lll.node_rx_adv_term) {
+					/* This should not be happening,
+					 * adv->is_enabled would be 0 if
+					 * node_rx_adv_term is released back to
+					 * pool.
+					 */
+					return BT_HCI_ERR_CMD_DISALLOWED;
+				}
+
+				/* Check advertising not terminated */
+				type = &adv->lll.node_rx_adv_term->type;
+				if (*type == NODE_RX_TYPE_NONE) {
+					/* Reset event counter, update duration,
+					 * and max events
+					 */
+					adv_max_events_duration_set(adv,
+						duration, max_ext_adv_evts);
+				}
+
+				/* Check the counter reset did not race with
+				 * advertising terminated.
+				 */
+				if (*type != NODE_RX_TYPE_NONE) {
+					/* Race with advertising terminated */
+					return BT_HCI_ERR_CMD_DISALLOWED;
+				}
+
+				/* FIXME: change random address in the primary
+				 *        or auxiliary PDU as necessary.
+				 */
+			}
+#endif /* CONFIG_BT_CTLR_ADV_EXT */
+
+			return 0;
+		}
+
+		/* Fail on being strict as a legacy controller, valid only under
+		 * Bluetooth Specification v4.x.
+		 * Bluetooth Specification v5.0 and above shall not fail to
+		 * enable already enabled advertising.
+		 */
 		return BT_HCI_ERR_CMD_DISALLOWED;
 	}
 
@@ -1100,16 +1172,16 @@ uint8_t ll_adv_enable(uint8_t enable)
 			return BT_HCI_ERR_MEM_CAPACITY_EXCEEDED;
 		}
 
+		node_rx_adv_term->hdr.type = NODE_RX_TYPE_NONE;
+
 		node_rx_adv_term->hdr.link = (void *)link_adv_term;
 		adv->lll.node_rx_adv_term = (void *)node_rx_adv_term;
+
+		adv_max_events_duration_set(adv, duration, max_ext_adv_evts);
 	}
 
 	const uint8_t phy = lll->phy_p;
 
-	adv->event_counter = 0;
-	adv->max_events = max_ext_adv_evts;
-	adv->ticks_remain_duration = HAL_TICKER_US_TO_TICKS((uint64_t)duration *
-							    10000);
 #else
 	/* Legacy ADV only supports LE_1M PHY */
 	const uint8_t phy = PHY_1M;
@@ -2189,6 +2261,16 @@ static void conn_release(struct ll_adv_set *adv)
 #endif /* CONFIG_BT_PERIPHERAL */
 
 #if defined(CONFIG_BT_CTLR_ADV_EXT)
+static void adv_max_events_duration_set(struct ll_adv_set *adv,
+					uint16_t duration,
+					uint8_t max_ext_adv_evts)
+{
+	adv->event_counter = 0;
+	adv->max_events = max_ext_adv_evts;
+	adv->ticks_remain_duration =
+		HAL_TICKER_US_TO_TICKS((uint64_t)duration * 10 * USEC_PER_MSEC);
+}
+
 static void ticker_op_aux_stop_cb(uint32_t status, void *param)
 {
 	uint8_t handle;
@@ -2253,6 +2335,14 @@ static inline uint8_t disable(uint8_t handle)
 
 	adv = ull_adv_is_enabled_get(handle);
 	if (!adv) {
+		/* Bluetooth Specification v5.0 Vol 2 Part E Section 7.8.9
+		 * Disabling advertising when it is already disabled has no
+		 * effect.
+		 */
+		if (!IS_ENABLED(CONFIG_BT_CTLR_ADV_ENABLE_STRICT)) {
+			return 0;
+		}
+
 		return BT_HCI_ERR_CMD_DISALLOWED;
 	}