drivers: bluetooth: silabs: Add separate thread for BT Link Layer

The BT Link Layer needs to get runtime in a timely manner to keep
connections alive and handle other time-critical tasks. This is achieved by
adding a separate thread for it with a meta-IRQ priority, which means it
can preempt other threads. The driver also has an RX thread that passes HCI
messages from the controller to the host stack. This can be a lower
priority cooperative thread, as it doesn't have strict timing requirements.

Signed-off-by: Kalle Kietäväinen <kalle.kietavainen@silabs.com>

drivers/bluetooth/hci/Kconfig.silabs

@@ -41,4 +41,9 @@ config BT_SILABS_EFR32_ACCEPT_LINK_LAYER_STACK_SIZE
 	default 1024
 	help
 	  Link layer stack size.
+
+config BT_SILABS_EFR32_LL_THREAD_PRIO
+	# Hidden option for Co-Operative Link Layer thread priority
+	def_int 0
+
 endmenu

drivers/bluetooth/hci/hci_silabs_efr32.c

@@ -5,6 +5,7 @@
  */
 
 #include <zephyr/drivers/bluetooth.h>
+#include <zephyr/kernel.h>
 
 #include <sl_btctrl_linklayer.h>
 #include <sl_hci_common_transport.h>
@@ -36,12 +37,18 @@ struct hci_data {
 static K_KERNEL_STACK_DEFINE(slz_ll_stack, CONFIG_BT_SILABS_EFR32_ACCEPT_LINK_LAYER_STACK_SIZE);
 static struct k_thread slz_ll_thread;
 
+static K_KERNEL_STACK_DEFINE(slz_rx_stack, CONFIG_BT_DRV_RX_STACK_SIZE);
+static struct k_thread slz_rx_thread;
+
 /* Semaphore for Link Layer */
 K_SEM_DEFINE(slz_ll_sem, 0, 1);
 
 /* Events mask for Link Layer */
 static atomic_t sli_btctrl_events;
 
+/* FIFO for received HCI packets */
+static struct k_fifo slz_rx_fifo;
+
 /* FIXME: these functions should come from the SiSDK headers! */
 void BTLE_LL_EventRaise(uint32_t events);
 void BTLE_LL_Process(uint32_t events);
@@ -73,8 +80,6 @@ void rail_isr_installer(void)
  */
 uint32_t hci_common_transport_transmit(uint8_t *data, int16_t len)
 {
-	const struct device *dev = DEVICE_DT_GET(DT_DRV_INST(0));
-	struct hci_data *hci = dev->data;
 	struct net_buf *buf;
 	uint8_t packet_type = data[0];
 	uint8_t event_code;
@@ -99,7 +104,7 @@ uint32_t hci_common_transport_transmit(uint8_t *data, int16_t len)
 	}
 
 	net_buf_add_mem(buf, data, len);
-	hci->recv(dev, buf);
+	k_fifo_put(&slz_rx_fifo, buf);
 
 	sl_btctrl_hci_transmit_complete(0);
 
@@ -140,7 +145,7 @@ done:
  * or an HCI event to pass upstairs. The BTLE_LL_Process function call will
  * take care of all of them, and add HCI events to the HCI queue when applicable.
  */
-static void slz_thread_func(void *p1, void *p2, void *p3)
+static void slz_ll_thread_func(void *p1, void *p2, void *p3)
 {
 	ARG_UNUSED(p1);
 	ARG_UNUSED(p2);
@@ -155,17 +160,40 @@ static void slz_thread_func(void *p1, void *p2, void *p3)
 	}
 }
 
+static void slz_rx_thread_func(void *p1, void *p2, void *p3)
+{
+	const struct device *dev = p1;
+	struct hci_data *hci = dev->data;
+
+	ARG_UNUSED(p2);
+	ARG_UNUSED(p3);
+
+	while (true) {
+		struct net_buf *buf = k_fifo_get(&slz_rx_fifo, K_FOREVER);
+
+		hci->recv(dev, buf);
+	}
+}
+
 static int slz_bt_open(const struct device *dev, bt_hci_recv_t recv)
 {
 	struct hci_data *hci = dev->data;
 	int ret;
 
-	/* Start RX thread */
+	BUILD_ASSERT(CONFIG_NUM_METAIRQ_PRIORITIES > 0,
-	k_thread_create(&slz_ll_thread, slz_ll_stack,
+		     "Config NUM_METAIRQ_PRIORITIES must be greater than 0");
-			K_KERNEL_STACK_SIZEOF(slz_ll_stack),
+	BUILD_ASSERT(CONFIG_BT_SILABS_EFR32_LL_THREAD_PRIO < CONFIG_NUM_METAIRQ_PRIORITIES,
-			slz_thread_func, NULL, NULL, NULL,
+		     "Config BT_SILABS_EFR32_LL_THREAD_PRIO must be a meta-IRQ priority");
-			K_PRIO_COOP(CONFIG_BT_DRIVER_RX_HIGH_PRIO), 0,
+
-			K_NO_WAIT);
+	k_fifo_init(&slz_rx_fifo);
+
+	k_thread_create(&slz_ll_thread, slz_ll_stack, K_KERNEL_STACK_SIZEOF(slz_ll_stack),
+			slz_ll_thread_func, NULL, NULL, NULL,
+			K_PRIO_COOP(CONFIG_BT_SILABS_EFR32_LL_THREAD_PRIO), 0, K_NO_WAIT);
+
+	k_thread_create(&slz_rx_thread, slz_rx_stack, K_KERNEL_STACK_SIZEOF(slz_rx_stack),
+			slz_rx_thread_func, (void *)dev, NULL, NULL,
+			K_PRIO_COOP(CONFIG_BT_DRIVER_RX_HIGH_PRIO), 0, K_NO_WAIT);
 
 	rail_isr_installer();
 	sl_rail_util_pa_init();

soc/silabs/Kconfig.defconfig

@@ -19,4 +19,7 @@ config CORTEX_M_SYSTICK
 config IDLE_STACK_SIZE
 	default 512 if SOC_GECKO_PM_BACKEND_PMGR
 
+configdefault NUM_METAIRQ_PRIORITIES
+	default 1 if BT_SILABS_EFR32
+
 endif