[nrf noup] Bluetooth: Mesh: zero randomization for friend's adv

Friend's replies on LPN's polls do not assume randomization in
advertiser. Zero randomization will help to optimize time when
LPN keeps receiving window open and save power.

Signed-off-by: Aleksandr Khromykh <[email protected]>

Author: alxelax

subsys/bluetooth/mesh/Kconfig

@@ -812,7 +812,7 @@ config BT_MESH_LPN_INIT_POLL_TIMEOUT
 config BT_MESH_LPN_SCAN_LATENCY
 	int "Latency for enabling scanning"
 	range 0 50
-	default 15
+	default 2
 	help
 	  Latency in milliseconds that it takes to enable scanning. This
 	  is in practice how much time in advance before the Receive Window

subsys/bluetooth/mesh/adv_ext.c

@@ -13,6 +13,9 @@
 #include <zephyr/bluetooth/bluetooth.h>
 #include <zephyr/bluetooth/hci.h>
 #include <zephyr/bluetooth/mesh.h>
+#if defined(CONFIG_BT_LL_SOFTDEVICE)
+#include <sdc_hci_vs.h>
+#endif
 
 #include "common/bt_str.h"
 
@@ -134,6 +137,28 @@ static inline struct bt_mesh_ext_adv *gatt_adv_get(void)
 #endif /* CONFIG_BT_MESH_ADV_EXT_GATT_SEPARATE */
 }
 
+static int set_adv_randomness(uint8_t handle, int rand_us)
+{
+#if defined(CONFIG_BT_LL_SOFTDEVICE)
+	struct net_buf *buf;
+	sdc_hci_cmd_vs_set_adv_randomness_t *cmd_params;
+
+	buf = bt_hci_cmd_create(SDC_HCI_OPCODE_CMD_VS_SET_ADV_RANDOMNESS, sizeof(*cmd_params));
+	if (!buf) {
+		LOG_ERR("Could not allocate command buffer");
+		return -ENOMEM;
+	}
+
+	cmd_params = net_buf_add(buf, sizeof(*cmd_params));
+	cmd_params->adv_handle = handle;
+	cmd_params->rand_us = rand_us;
+
+	return bt_hci_cmd_send_sync(SDC_HCI_OPCODE_CMD_VS_SET_ADV_RANDOMNESS, buf, NULL);
+#else
+	return 0;
+#endif /* defined(CONFIG_BT_LL_SOFTDEVICE) */
+}
+
 static int adv_start(struct bt_mesh_ext_adv *adv,
 		     const struct bt_le_adv_param *param,
 		     struct bt_le_ext_adv_start_param *start,
@@ -456,6 +481,13 @@ int bt_mesh_adv_enable(void)
 		if (err) {
 			return err;
 		}
+
+		if (IS_ENABLED(CONFIG_BT_LL_SOFTDEVICE) && adv->tag & BT_MESH_FRIEND_ADV) {
+			err = set_adv_randomness(adv->instance->handle, 0);
+			if (err) {
+				LOG_ERR("Failed to set zero randomness: %d", err);
+			}
+		}
 	}
 
 	return 0;