drivers: dp: swdp_bitbang: power optimization

This patch changes GPIO initialization
to be in PORT_OFF state by default.
Also, if no transceiver is attached to the signals,
the GPIOs are configured to be disconnected to preserve power.

I tested this on a prototype board where we are going to have
a debugger in a low-power context.

Signed-off-by: Maximilian Deubel <[email protected]>

Author: maxd-nordic

drivers/dp/swdp_bitbang.c

@@ -568,107 +568,125 @@ static int sw_configure(const struct device *dev,
 static int sw_port_on(const struct device *dev)
 {
 	const struct sw_config *config = dev->config;
-
-	gpio_pin_set_dt(&config->clk, 1);
+	int ret;
 
 	if (config->dnoe.port) {
-		gpio_pin_set_dt(&config->dnoe, 1);
+		ret = gpio_pin_configure_dt(&config->dnoe, GPIO_OUTPUT_ACTIVE);
+		if (ret) {
+			return ret;
+		}
 	}
 
 	if (config->dout.port) {
-		gpio_pin_set_dt(&config->dout, 1);
-	} else {
-		int ret;
-
-		ret = gpio_pin_configure_dt(&config->dio, GPIO_OUTPUT_ACTIVE);
+		ret = gpio_pin_configure_dt(&config->dout, GPIO_OUTPUT_ACTIVE);
 		if (ret) {
 			return ret;
 		}
 	}
 
-	if (config->noe.port) {
-		gpio_pin_set_dt(&config->noe, 1);
-	}
-	if (config->reset.port) {
-		gpio_pin_set_dt(&config->reset, 1);
-	}
-
-	return 0;
-}
-
-static int sw_port_off(const struct device *dev)
-{
-	const struct sw_config *config = dev->config;
-
-	if (config->dnoe.port) {
-		gpio_pin_set_dt(&config->dnoe, 0);
+	ret = gpio_pin_configure_dt(&config->dio, GPIO_INPUT);
+	if (ret) {
+		return ret;
 	}
 
-	if (config->dout.port) {
-		gpio_pin_set_dt(&config->dout, 0);
-	} else {
-		int ret;
-
-		ret = gpio_pin_configure_dt(&config->dio, GPIO_INPUT);
+	if (config->noe.port) {
+		ret = gpio_pin_configure_dt(&config->noe, GPIO_OUTPUT_ACTIVE);
 		if (ret) {
 			return ret;
 		}
 	}
 
-	if (config->noe.port) {
-		gpio_pin_set_dt(&config->noe, 0);
+	ret = gpio_pin_configure_dt(&config->clk, GPIO_OUTPUT_ACTIVE);
+	if (ret) {
+		return ret;
 	}
-	if (config->reset.port) {
-		gpio_pin_set_dt(&config->reset, 1);
+
+	ret = gpio_pin_configure_dt(&config->reset, GPIO_OUTPUT_ACTIVE);
+	if (ret) {
+		return ret;
 	}
 
 	return 0;
 }
 
-static int sw_gpio_init(const struct device *dev)
+static int sw_port_off(const struct device *dev)
 {
 	const struct sw_config *config = dev->config;
-	struct sw_cfg_data *sw_data = dev->data;
 	int ret;
 
-	ret = gpio_pin_configure_dt(&config->clk, GPIO_OUTPUT_ACTIVE);
-	if (ret) {
-		return ret;
-	}
+	/* If there is a transceiver connected to IO, pins should always be driven. */
+	if (config->dnoe.port) {
+		ret = gpio_pin_configure_dt(&config->dnoe, GPIO_OUTPUT_INACTIVE);
+		if (ret) {
+			return ret;
+		}
 
-	ret = gpio_pin_configure_dt(&config->dio, GPIO_INPUT);
-	if (ret) {
-		return ret;
-	}
+		if (config->dout.port) {
+			ret = gpio_pin_configure_dt(&config->dout, GPIO_OUTPUT_ACTIVE);
+			if (ret) {
+				return ret;
+			}
+		}
 
-	if (config->dout.port) {
-		ret = gpio_pin_configure_dt(&config->dout, GPIO_OUTPUT_ACTIVE);
+		ret = gpio_pin_configure_dt(&config->dio, GPIO_INPUT);
 		if (ret) {
 			return ret;
 		}
-	}
+	} else {
+		if (config->dout.port) {
+			ret = gpio_pin_configure_dt(&config->dout, GPIO_DISCONNECTED);
+			if (ret) {
+				return ret;
+			}
+		}
 
-	if (config->dnoe.port) {
-		ret = gpio_pin_configure_dt(&config->dnoe, GPIO_OUTPUT_INACTIVE);
+		ret = gpio_pin_configure_dt(&config->dio, GPIO_DISCONNECTED);
 		if (ret) {
 			return ret;
 		}
 	}
 
+	/* If there is a transceiver connected to CLK, pins should always be driven. */
 	if (config->noe.port) {
 		ret = gpio_pin_configure_dt(&config->noe, GPIO_OUTPUT_INACTIVE);
 		if (ret) {
 			return ret;
 		}
+
+		ret = gpio_pin_configure_dt(&config->clk, GPIO_OUTPUT_ACTIVE);
+		if (ret) {
+			return ret;
+		}
+
+	} else {
+		ret = gpio_pin_configure_dt(&config->clk, GPIO_DISCONNECTED);
+		if (ret) {
+			return ret;
+		}
 	}
 
 	if (config->reset.port) {
-		ret = gpio_pin_configure_dt(&config->reset, GPIO_OUTPUT_ACTIVE);
+		ret = gpio_pin_configure_dt(&config->reset, GPIO_DISCONNECTED);
 		if (ret) {
 			return ret;
 		}
 	}
 
+	return 0;
+}
+
+static int sw_gpio_init(const struct device *dev)
+{
+	const struct sw_config *config = dev->config;
+	struct sw_cfg_data *sw_data = dev->data;
+	int ret;
+
+	/* start with the port turned off */
+	ret = sw_port_off(dev);
+	if (ret) {
+		return ret;
+	}
+
 	sw_data->turnaround = 1U;
 	sw_data->data_phase = false;
 	sw_data->fast_clock = false;