modem: backend: uart: Add hw-flow-control for UART

Add Asynchronous UART implementation, which does not drop data
when automatic hardware-flow-control is set in the device tree.

With automatic hardware flow control, the CTS pin will be
automatically deactivated when there are no more asynchronous
UART RX buffers available. After buffer space becomes available,
and UART RX is restarted, the CTS pin will be activated.

Signed-off-by: Markus Lassila <[email protected]>

Author: MarkusLassila

include/zephyr/modem/backend/uart.h

@@ -30,6 +30,25 @@ struct modem_backend_uart_isr {
 	uint32_t transmit_buf_put_limit;
 };
 
+#if CONFIG_MODEM_BACKEND_UART_ASYNC_HWFC_ENABLED
+struct rx_queue_event_t {
+	uint8_t *buf;
+	size_t len;
+};
+
+struct modem_backend_uart_async {
+	struct k_mem_slab rx_slab;
+	struct k_msgq rx_queue;
+	struct rx_queue_event_t rx_event;
+	struct rx_queue_event_t rx_queue_buf[CONFIG_MODEM_BACKEND_UART_ASYNC_HWFC_BUFFER_COUNT];
+	uint32_t rx_buf_size;
+	uint8_t rx_buf_count;
+	uint8_t *transmit_buf;
+	uint32_t transmit_buf_size;
+	struct k_work rx_disabled_work;
+	atomic_t state;
+};
+#else
 struct modem_backend_uart_async {
 	uint8_t *receive_bufs[2];
 	uint32_t receive_buf_size;
@@ -40,7 +59,7 @@ struct modem_backend_uart_async {
 	struct k_work rx_disabled_work;
 	atomic_t state;
 };
-
+#endif /* CONFIG_MODEM_BACKEND_UART_ASYNC_HWFC_ENABLED */
 struct modem_backend_uart {
 	const struct device *uart;
 	struct modem_pipe pipe;
@@ -60,7 +79,7 @@ struct modem_backend_uart {
 
 struct modem_backend_uart_config {
 	const struct device *uart;
-	uint8_t *receive_buf;
+	uint8_t *receive_buf __aligned(sizeof(uint32_t));
 	uint32_t receive_buf_size;
 	uint8_t *transmit_buf;
 	uint32_t transmit_buf_size;

subsys/modem/backends/CMakeLists.txt

@@ -6,4 +6,5 @@ zephyr_library()
 zephyr_library_sources_ifdef(CONFIG_MODEM_BACKEND_TTY modem_backend_tty.c)
 zephyr_library_sources_ifdef(CONFIG_MODEM_BACKEND_UART modem_backend_uart.c)
 zephyr_library_sources_ifdef(CONFIG_MODEM_BACKEND_UART_ISR modem_backend_uart_isr.c)
-zephyr_library_sources_ifdef(CONFIG_MODEM_BACKEND_UART_ASYNC modem_backend_uart_async.c)
+zephyr_library_sources_ifdef(CONFIG_MODEM_BACKEND_UART_ASYNC_HWFC_DISABLED modem_backend_uart_async.c)
+zephyr_library_sources_ifdef(CONFIG_MODEM_BACKEND_UART_ASYNC_HWFC_ENABLED modem_backend_uart_async_hwfc.c)

subsys/modem/backends/Kconfig

@@ -48,6 +48,29 @@ config MODEM_BACKEND_UART_ASYNC_RECEIVE_IDLE_TIMEOUT_MS
 	int "Modem async UART receive idle timeout in milliseconds"
 	default 30
 
+choice MODEM_BACKEND_UART_ASYNC_HWFC_CHOICE
+	prompt "Modem async UART hardware flow control"
+	default MODEM_BACKEND_UART_ASYNC_HWFC_DISABLED
+	help
+	  Select whether to enable or disable hardware flow control (HWFC)
+	  for the modem async UART backend.
+
+config MODEM_BACKEND_UART_ASYNC_HWFC_DISABLED
+	bool "Hardware flow control is disabled"
+
+config MODEM_BACKEND_UART_ASYNC_HWFC_ENABLED
+	bool "Hardware flow control is enabled"
+	select EXPERIMENTAL
+endchoice
+
+if MODEM_BACKEND_UART_ASYNC_HWFC_ENABLED
+
+config MODEM_BACKEND_UART_ASYNC_HWFC_BUFFER_COUNT
+	int "Modem async UART buffer count"
+	range 2 4
+	default 3
 endif
 
+endif # MODEM_BACKEND_UART_ASYNC
+
 endif # MODEM_BACKEND_UART

subsys/modem/backends/modem_backend_uart.c

@@ -45,7 +45,9 @@ struct modem_pipe *modem_backend_uart_init(struct modem_backend_uart *backend,
 
 #ifdef CONFIG_MODEM_BACKEND_UART_ASYNC
 	if (modem_backend_uart_async_is_supported(backend)) {
-		modem_backend_uart_async_init(backend, config);
+		if (modem_backend_uart_async_init(backend, config)) {
+			return NULL;
+		}
 		return &backend->pipe;
 	}
 #endif /* CONFIG_MODEM_BACKEND_UART_ASYNC */

subsys/modem/backends/modem_backend_uart_async.c

@@ -310,8 +310,8 @@ static void init_stats(struct modem_backend_uart *backend)
 }
 #endif
 
-void modem_backend_uart_async_init(struct modem_backend_uart *backend,
-				   const struct modem_backend_uart_config *config)
+int modem_backend_uart_async_init(struct modem_backend_uart *backend,
+				  const struct modem_backend_uart_config *config)
 {
 	uint32_t receive_buf_size_quarter = config->receive_buf_size / 4;
 
@@ -332,4 +332,6 @@ void modem_backend_uart_async_init(struct modem_backend_uart *backend,
 #if CONFIG_MODEM_STATS
 	init_stats(backend);
 #endif
+
+	return 0;
 }

subsys/modem/backends/modem_backend_uart_async.h

@@ -15,8 +15,8 @@ extern "C" {
 
 bool modem_backend_uart_async_is_supported(struct modem_backend_uart *backend);
 
-void modem_backend_uart_async_init(struct modem_backend_uart *backend,
-				   const struct modem_backend_uart_config *config);
+int modem_backend_uart_async_init(struct modem_backend_uart *backend,
+				  const struct modem_backend_uart_config *config);
 
 #ifdef __cplusplus
 }