lib: nrf_modem: trace: fixes for uart trace backend++

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -404,8 +404,13 @@ Modem libraries
 
 * :ref:`nrf_modem_lib_readme`:
 
-  * Fixed a rare bug that caused a deadlock between two threads when one thread sent data while the other received a lot of data quickly.
-  * Updated the :c:func:`nrf_modem_lib_shutdown` function to allow the modem to be in flight mode (``CFUN=4``) when shutting down the modem.
+  * Added CEREG event tracking to ``lte_connectivity``.
+
+  * Updated:
+
+    * The :c:func:`nrf_modem_lib_shutdown` function to allow the modem to be in flight mode (``CFUN=4``) when shutting down the modem.
+    * The trace backends can now return ``-EAGAIN`` if the write operation can be retried.
+    * Fixed a rare bug that caused a deadlock between two threads when one thread sent data while the other received a lot of data quickly.
 
 * :ref:`lib_location` library:
 
@@ -415,10 +420,9 @@ Modem libraries
 
   * Updated the library to allow a ``PDP_type``-only configuration in the :c:func:`pdn_ctx_configure` function.
 
-* :ref:`nrf_modem_lib_readme`:
+* :ref:`modem_key_mgmt`:
 
    * Updated the :c:func:`modem_key_mgmt_cmp` function to return ``1`` if the buffer length does not match the certificate length.
-   * Added CEREG event tracking to ``lte_connectivity``.
 
 Libraries for networking
 ------------------------

include/modem/trace_backend.h

@@ -58,6 +58,8 @@ struct nrf_modem_lib_trace_backend {
 	 *          -ENOSPC if no space is available and the backend has to be cleared before
 	 *                  tracing can continue. For some trace backends, space is also cleared
 	 *                  when performing the read operation.
+	 *          -EAGAIN if no data were written due to e.g. flow control and the operation
+	 *                  should be retried.
 	 */
 	int (*write)(const void *data, size_t len);
 

lib/nrf_modem_lib/nrf_modem_lib_trace.c

@@ -204,6 +204,21 @@ static int trace_fragment_write(struct nrf_modem_trace_data *frag)
 
 		__ASSERT(ret != 0, "Trace backend wrote 0 bytes");
 
+		/* We handle this here and not in the trace_thread_handler as we might not write the
+		 * entire trace fragment in the same write operation. If we get EAGAIN on the
+		 * second, third, ..., we would repeat sending the first section of the trace
+		 * fragment.
+		 */
+		if (ret == -EAGAIN) {
+			/* We don't allow retrying if the modem is shut down as that can block
+			 * a new modem init.
+			 */
+			if (!nrf_modem_is_initialized()) {
+				return -ESHUTDOWN;
+			}
+			continue;
+		}
+
 		if (ret < 0) {
 			LOG_ERR("trace_backend.write failed with err: %d", ret);
 			return ret;
@@ -347,6 +362,19 @@ static int trace_deinit(void)
 		return err;
 	}
 
+
+#if CONFIG_NRF_MODEM_LIB_TRACE_BACKEND_BITRATE
+	k_work_cancel(&backend_bps_avg_update_work);
+#endif
+
+#if CONFIG_NRF_MODEM_LIB_TRACE_BACKEND_BITRATE_LOG
+	k_work_cancel(&backend_bps_log_work);
+#endif
+
+#if CONFIG_NRF_MODEM_LIB_TRACE_BITRATE_LOG
+	k_work_cancel(&bps_log_work);
+#endif
+
 	k_sem_give(&trace_done_sem);
 
 	return 0;

lib/nrf_modem_lib/trace_backends/uart/uart.c

@@ -158,6 +158,11 @@ int trace_backend_write(const void *data, size_t len)
 	ret = len - remaining_bytes;
 out:
 	k_sem_give(&tx_sem);
+
+	if (ret == 0) {
+		return -EAGAIN;
+	}
+
 	return ret;
 }
 

snippets/nrf91-modem-trace-uart/overlay-modem-trace-uart.conf

@@ -13,3 +13,5 @@ CONFIG_NRF_MODEM_LIB_TRACE_BACKEND_UART_ZEPHYR=y
 # UART configuration
 CONFIG_SERIAL=y
 CONFIG_UART_ASYNC_API=y
+CONFIG_UART_1_ASYNC=y
+CONFIG_UART_1_INTERRUPT_DRIVEN=n