drivers: serial: bt: Use dedicated Workqueue

Stop relying on the system workqueue, as the BT TX APIs should
potentially block and now by design this will not work with the
Bluetooth Stack (for good reasons). Now the UART NUS driver has a
dedicated workqueue, which all NUS instances share.

Signed-off-by: Luis Ubieda <luisf@croxel.com>

Author: ubieda

drivers/serial/uart_bt.c

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <zephyr/kernel.h>
 #include <zephyr/drivers/uart.h>
 #include <zephyr/sys/ring_buffer.h>
 #include <zephyr/sys/atomic.h>
@@ -14,6 +15,9 @@
 #include <zephyr/logging/log.h>
 LOG_MODULE_REGISTER(uart_nus, CONFIG_UART_LOG_LEVEL);
 
+K_THREAD_STACK_DEFINE(nus_work_queue_stack, 2048);
+static struct k_work_q nus_work_queue;
+
 struct uart_bt_data {
 	struct {
 		struct bt_nus_inst *inst;
@@ -47,7 +51,7 @@ static void bt_notif_enabled(bool enabled, void *ctx)
 	LOG_DBG("%s() - %s", __func__, enabled ? "enabled" : "disabled");
 
 	if (!ring_buf_is_empty(dev_data->uart.tx_ringbuf)) {
-		k_work_reschedule(&dev_data->uart.tx_work, K_NO_WAIT);
+		k_work_reschedule_for_queue(&nus_work_queue, &dev_data->uart.tx_work, K_NO_WAIT);
 	}
 }
 
@@ -71,7 +75,7 @@ static void bt_received(struct bt_conn *conn, const void *data, uint16_t len, vo
 		LOG_ERR("RX Ring buffer full. received: %d, added to queue: %d", len, put_len);
 	}
 
-	k_work_submit(&dev_data->uart.cb_work);
+	k_work_submit_to_queue(&nus_work_queue, &dev_data->uart.cb_work);
 }
 
 static void cb_work_handler(struct k_work *work)
@@ -113,7 +117,7 @@ static void tx_work_handler(struct k_work *work)
 	} while (len > 0 && !err);
 
 	if ((ring_buf_space_get(dev_data->uart.tx_ringbuf) > 0) && dev_data->uart.tx_irq_ena) {
-		k_work_submit(&dev_data->uart.cb_work);
+		k_work_submit_to_queue(&nus_work_queue, &dev_data->uart.cb_work);
 	}
 }
 
@@ -128,7 +132,7 @@ static int uart_bt_fifo_fill(const struct device *dev, const uint8_t *tx_data, i
 	}
 
 	if (atomic_get(&dev_data->bt.enabled)) {
-		k_work_reschedule(&dev_data->uart.tx_work, K_NO_WAIT);
+		k_work_reschedule_for_queue(&nus_work_queue, &dev_data->uart.tx_work, K_NO_WAIT);
 	}
 
 	return wrote;
@@ -169,7 +173,7 @@ static void uart_bt_poll_out(const struct device *dev, unsigned char c)
 		 * data, so more than one byte is transmitted (e.g: when poll_out is
 		 * called inside a for-loop).
 		 */
-		k_work_schedule(&dev_data->uart.tx_work, K_MSEC(1));
+		k_work_schedule_for_queue(&nus_work_queue, &dev_data->uart.tx_work, K_MSEC(1));
 	}
 }
 
@@ -191,7 +195,7 @@ static void uart_bt_irq_tx_enable(const struct device *dev)
 	dev_data->uart.tx_irq_ena = true;
 
 	if (uart_bt_irq_tx_ready(dev)) {
-		k_work_submit(&dev_data->uart.cb_work);
+		k_work_submit_to_queue(&nus_work_queue, &dev_data->uart.cb_work);
 	}
 }
 
@@ -219,7 +223,7 @@ static void uart_bt_irq_rx_enable(const struct device *dev)
 
 	dev_data->uart.rx_irq_ena = true;
 
-	k_work_submit(&dev_data->uart.cb_work);
+	k_work_submit_to_queue(&nus_work_queue, &dev_data->uart.cb_work);
 }
 
 static void uart_bt_irq_rx_disable(const struct device *dev)
@@ -267,6 +271,19 @@ static const struct uart_driver_api uart_bt_driver_api = {
 	.irq_callback_set = uart_bt_irq_callback_set,
 };
 
+static int uart_bt_workqueue_init(void)
+{
+	k_work_queue_init(&nus_work_queue);
+	k_work_queue_start(&nus_work_queue, nus_work_queue_stack,
+			   K_THREAD_STACK_SIZEOF(nus_work_queue_stack),
+			   K_LOWEST_APPLICATION_THREAD_PRIO, NULL);
+
+	return 0;
+}
+
+/** The work-queue is shared across all instances, hence we initialize it separatedly */
+SYS_INIT(uart_bt_workqueue_init, POST_KERNEL, CONFIG_SERIAL_INIT_PRIORITY);
+
 static int uart_bt_init(const struct device *dev)
 {
 	int err;