usbd: device_next: cdc: wait IN EP ready before enqueue data to EP

Under the current structure of usbd_cdc_acm, there is a possibility that
TX data is enqueued to UDC driver before the previous transaction is
completed, hence causing the dropped data. This commit adds a mechanism
for usbd_cdc_acm driver to wait for IN endpoint to complete existing
transaction before allows the subsequent transaction to be enqueued.

Signed-off-by: Chew Zeh Yang <[email protected]>

usbd: device_next: cdc: fix possible CPU hogging issue

As pointed out by tmon-nordic, the method to re-queue CDC tx transaction
has possible issue of CPU hogging that could start system workqueue and
lower priority thread. Instead of keep requeing the tx_fifo work, simply
raise altered flag. The pending TX transaction will be triggered when
TX transfer completion interrupt is raised.

Signed-off-by: Chew Zeh Yang <[email protected]>

subsys/usb/device_next/class/usbd_cdc_acm.c

@@ -48,6 +48,7 @@ UDC_BUF_POOL_DEFINE(cdc_acm_ep_pool,
 #define CDC_ACM_IRQ_TX_ENABLED		3
 #define CDC_ACM_RX_FIFO_BUSY		4
 #define CDC_ACM_LOCK			5
+#define CDC_ACM_TX_EP_BUSY              6
 
 static struct k_work_q cdc_acm_work_q;
 static K_KERNEL_STACK_DEFINE(cdc_acm_stack,
@@ -215,6 +216,8 @@ static int usbd_cdc_acm_request(struct usbd_class_data *const c_data,
 
 		if (bi->ep == cdc_acm_get_bulk_out(c_data)) {
 			atomic_clear_bit(&data->state, CDC_ACM_RX_FIFO_BUSY);
+		} else if (bi->ep == cdc_acm_get_bulk_in(c_data)) {
+			atomic_clear_bit(&data->state, CDC_ACM_TX_EP_BUSY);
 		}
 
 		goto ep_request_error;
@@ -236,6 +239,7 @@ static int usbd_cdc_acm_request(struct usbd_class_data *const c_data,
 
 	if (bi->ep == cdc_acm_get_bulk_in(c_data)) {
 		/* TX transfer completion */
+		atomic_clear_bit(&data->state, CDC_ACM_TX_EP_BUSY);
 		if (data->cb) {
 			cdc_acm_work_submit(&data->irq_cb_work);
 		}
@@ -540,6 +544,11 @@ static void cdc_acm_tx_fifo_handler(struct k_work *work)
 		return;
 	}
 
+	if (atomic_test_and_set_bit(&data->state, CDC_ACM_TX_EP_BUSY)) {
+		data->tx_fifo.altered = true;
+		goto tx_fifo_handler_exit;
+	}
+
 	buf = cdc_acm_buf_alloc(cdc_acm_get_bulk_in(c_data));
 	if (buf == NULL) {
 		cdc_acm_work_submit(&data->tx_fifo_work);