[nrf fromlist] drivers: modem: Implement support for DTR signal

DTR signal on UART extends the power saving by allowing host
to indicate the remote end that the UART is not in active state.

Upstream PR #: 98145

Signed-off-by: Seppo Takalo <[email protected]>

Author: SeppoTakalo

drivers/modem/modem_cellular.c

@@ -185,6 +185,7 @@ struct modem_cellular_config {
 	struct gpio_dt_spec power_gpio;
 	struct gpio_dt_spec reset_gpio;
 	struct gpio_dt_spec wake_gpio;
+	struct gpio_dt_spec dtr_gpio;
 	uint16_t power_pulse_duration_ms;
 	uint16_t reset_pulse_duration_ms;
 	uint16_t startup_time_ms;
@@ -2095,6 +2096,7 @@ static int modem_cellular_init(const struct device *dev)
 {
 	struct modem_cellular_data *data = (struct modem_cellular_data *)dev->data;
 	struct modem_cellular_config *config = (struct modem_cellular_config *)dev->config;
+	const struct gpio_dt_spec *dtr_gpio = NULL;
 
 	data->dev = dev;
 
@@ -2118,9 +2120,15 @@ static int modem_cellular_init(const struct device *dev)
 		gpio_pin_configure_dt(&config->reset_gpio, GPIO_OUTPUT_ACTIVE);
 	}
 
+	if (modem_cellular_gpio_is_enabled(&config->dtr_gpio)) {
+		gpio_pin_configure_dt(&config->dtr_gpio, GPIO_OUTPUT_INACTIVE);
+		dtr_gpio = &config->dtr_gpio;
+	}
+
 	{
 		const struct modem_backend_uart_config uart_backend_config = {
 			.uart = config->uart,
+			.dtr_gpio = dtr_gpio,
 			.receive_buf = data->uart_backend_receive_buf,
 			.receive_buf_size = ARRAY_SIZE(data->uart_backend_receive_buf),
 			.transmit_buf = data->uart_backend_transmit_buf,
@@ -2888,6 +2896,7 @@ MODEM_CHAT_SCRIPT_DEFINE(sqn_gm02s_periodic_chat_script,
 		.power_gpio = GPIO_DT_SPEC_INST_GET_OR(inst, mdm_power_gpios, {}),                 \
 		.reset_gpio = GPIO_DT_SPEC_INST_GET_OR(inst, mdm_reset_gpios, {}),                 \
 		.wake_gpio = GPIO_DT_SPEC_INST_GET_OR(inst, mdm_wake_gpios, {}),                   \
+		.dtr_gpio = GPIO_DT_SPEC_INST_GET_OR(inst, mdm_dtr_gpios, {}),                     \
 		.power_pulse_duration_ms = (power_ms),                                             \
 		.reset_pulse_duration_ms = (reset_ms),                                             \
 		.startup_time_ms  = (startup_ms),                                                  \

dts/bindings/modem/zephyr,cellular-modem-device.yaml

@@ -17,3 +17,11 @@ properties:
   mdm-wake-gpios:
     type: phandle-array
     description: GPIO for modem wake
+
+  mdm-dtr-gpios:
+    type: phandle-array
+    description: |
+      GPIO for modem data terminal ready.
+
+      Asserted (logical high) when UART is active and
+      deasserted (logical low) when UART is inactive, powered down or in low power mode.

include/zephyr/modem/backend/uart.h

@@ -68,6 +68,7 @@ struct modem_backend_uart_async {
 
 struct modem_backend_uart {
 	const struct device *uart;
+	const struct gpio_dt_spec *dtr_gpio;
 	struct modem_pipe pipe;
 	struct k_work_delayable receive_ready_work;
 	struct k_work transmit_idle_work;
@@ -85,6 +86,7 @@ struct modem_backend_uart {
 
 struct modem_backend_uart_config {
 	const struct device *uart;
+	const struct gpio_dt_spec *dtr_gpio;
 	/* Address must be word-aligned when CONFIG_MODEM_BACKEND_UART_ASYNC_HWFC is enabled. */
 	uint8_t *receive_buf;
 	uint32_t receive_buf_size;

subsys/modem/backends/modem_backend_uart.c

@@ -39,6 +39,7 @@ struct modem_pipe *modem_backend_uart_init(struct modem_backend_uart *backend,
 
 	memset(backend, 0x00, sizeof(*backend));
 	backend->uart = config->uart;
+	backend->dtr_gpio = config->dtr_gpio;
 	k_work_init_delayable(&backend->receive_ready_work,
 			      modem_backend_uart_receive_ready_handler);
 	k_work_init(&backend->transmit_idle_work, modem_backend_uart_transmit_idle_handler);

subsys/modem/backends/modem_backend_uart_async.c

@@ -11,6 +11,7 @@
 LOG_MODULE_REGISTER(modem_backend_uart_async, CONFIG_MODEM_MODULES_LOG_LEVEL);
 
 #include <zephyr/kernel.h>
+#include <zephyr/drivers/gpio.h>
 #include <string.h>
 
 enum {
@@ -157,6 +158,10 @@ static int modem_backend_uart_async_open(void *data)
 	atomic_clear(&backend->async.common.state);
 	ring_buf_reset(&backend->async.receive_rb);
 
+	if (backend->dtr_gpio) {
+		gpio_pin_set_dt(backend->dtr_gpio, 1);
+	}
+
 	atomic_set_bit(&backend->async.common.state,
 		       MODEM_BACKEND_UART_ASYNC_STATE_RX_BUF0_USED_BIT);
 	atomic_set_bit(&backend->async.common.state, MODEM_BACKEND_UART_ASYNC_STATE_RECEIVING_BIT);
@@ -268,6 +273,9 @@ static int modem_backend_uart_async_close(void *data)
 	atomic_clear_bit(&backend->async.common.state, MODEM_BACKEND_UART_ASYNC_STATE_OPEN_BIT);
 	uart_tx_abort(backend->uart);
 	uart_rx_disable(backend->uart);
+	if (backend->dtr_gpio) {
+		gpio_pin_set_dt(backend->dtr_gpio, 0);
+	}
 	return 0;
 }
 

subsys/modem/backends/modem_backend_uart_async_hwfc.c

@@ -11,6 +11,7 @@
 LOG_MODULE_REGISTER(modem_backend_uart_async_hwfc, CONFIG_MODEM_MODULES_LOG_LEVEL);
 
 #include <zephyr/kernel.h>
+#include <zephyr/drivers/gpio.h>
 #include <string.h>
 
 struct rx_buf_t {
@@ -221,6 +222,10 @@ static int modem_backend_uart_async_hwfc_open(void *data)
 		return -ENOMEM;
 	}
 
+	if (backend->dtr_gpio) {
+		gpio_pin_set_dt(backend->dtr_gpio, 1);
+	}
+
 	atomic_clear(&backend->async.common.state);
 	atomic_set_bit(&backend->async.common.state, MODEM_BACKEND_UART_ASYNC_STATE_OPEN_BIT);
 
@@ -357,6 +362,9 @@ static int modem_backend_uart_async_hwfc_close(void *data)
 		uart_rx_disable(backend->uart);
 	}
 
+	if (backend->dtr_gpio) {
+		gpio_pin_set_dt(backend->dtr_gpio, 0);
+	}
 	return 0;
 }