wireless/bluetooth: Add option to set the HCI TX thread affinity

By enabling the config `CONFIG_BLUETOOTH_TXCMD_PINNED_TO_CORE` and
setting the value of `CONFIG_BLUETOOTH_TXCMD_CORE`, it's possible
to pin the HCI TX thread to a specific core on a SMP-enabled setup.
This is necessary for devices that require that the function that
sends data (`bt_send`) to be called from a specific core.

wireless/bluetooth/Kconfig

@@ -193,6 +193,25 @@ config BLUETOOTH_TXCONN_NMSGS
 	int "Tx connection thread mqueue size"
 	default 16
 
+config BLUETOOTH_TXCMD_PINNED_TO_CORE
+	bool "Pin Tx command thread to specific core"
+	depends on SMP
+	default n
+	---help---
+		This option enables us to set the affinity of the Tx command thread
+		to make it run on a specific core.
+
+if BLUETOOTH_TXCMD_PINNED_TO_CORE
+
+config BLUETOOTH_TXCMD_CORE
+	int "Tx command thread CPU core"
+	default 1
+	range 1 SMP_NCPUS
+	---help---
+		Select the core to pin the Tx command thread.
+
+endif # BLUETOOTH_TXCMD_PINNED_TO_CORE
+
 endmenu # Kernel Thread Configuration
 
 config BLUETOOTH_SMP_SELFTEST

wireless/bluetooth/bt_hcicore.c

@@ -1499,6 +1499,10 @@ static void cmd_queue_deinit(void)
 static void cmd_queue_init(void)
 {
   int ret;
+#ifdef CONFIG_BLUETOOTH_TXCMD_PINNED_TO_CORE
+  cpu_set_t cpuset;
+#endif
+  int pid;
 
   /* When there is a command to be sent to the Bluetooth driver, it queued on
    * the Tx queue and received by logic on the Tx kernel thread.
@@ -1512,10 +1516,29 @@ static void cmd_queue_init(void)
 
   g_btdev.ncmd = 1;
   g_btdev.tx_status = OK;
-  ret = kthread_create("BT HCI Tx", CONFIG_BLUETOOTH_TXCMD_PRIORITY,
+
+#ifdef CONFIG_BLUETOOTH_TXCMD_PINNED_TO_CORE
+  sched_lock();
+#endif
+
+  pid = kthread_create("BT HCI Tx", CONFIG_BLUETOOTH_TXCMD_PRIORITY,
                        CONFIG_BLUETOOTH_TXCMD_STACKSIZE,
                        hci_tx_kthread, NULL);
-  DEBUGASSERT(ret > 0);
+  DEBUGASSERT(pid > 0);
+
+#ifdef CONFIG_BLUETOOTH_TXCMD_PINNED_TO_CORE
+  CPU_ZERO(&cpuset);
+  CPU_SET((CONFIG_BLUETOOTH_TXCMD_CORE - 1), &cpuset);
+  ret = nxsched_set_affinity(pid, sizeof(cpuset), &cpuset);
+  if (ret)
+    {
+      wlerr("Failed to set affinity error=%d\n", ret);
+      DEBUGPANIC();
+    }
+
+  sched_unlock();
+#endif
+
   UNUSED(ret);
 }