[PATCH] pps-gpio: implement echo pulses

[Lukas Senger <lukas@fridolin.com>]

pps-gpio reports as having echo capability via sysfs, which is not
actually the case. This patch implements it.

The output pin is hardcoded as 17. This should probably be configurable
via the dtoverlay in the same way as the input pin.
---
 drivers/pps/clients/pps-gpio.c | 55 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 50 insertions(+), 5 deletions(-)

diff --git a/drivers/pps/clients/pps-gpio.c b/drivers/pps/clients/pps-gpio.c
index 333ad7d5..dd7624f1 100644
--- a/drivers/pps/clients/pps-gpio.c
+++ b/drivers/pps/clients/pps-gpio.c
@@ -35,6 +35,12 @@
 #include <linux/list.h>
 #include <linux/of_device.h>
 #include <linux/of_gpio.h>
+#include <linux/delay.h>
+
+/* TODO: this should work like gpio_pin below but I don't know how to work with
+ * devicetree overlays.
+ */
+#define PPS_GPIO_ECHO_PIN 17
 
 /* Info for each registered platform device */
 struct pps_gpio_device_data {
@@ -63,16 +69,41 @@ static irqreturn_t pps_gpio_irq_handler(int irq, void *data)
 
 	rising_edge = gpio_get_value(info->gpio_pin);
 	if ((rising_edge && !info->assert_falling_edge) ||
-			(!rising_edge && info->assert_falling_edge))
+			(!rising_edge && info->assert_falling_edge)) {
+		if (info->pps->params.mode & PPS_ECHOASSERT) {
+			gpio_set_value(PPS_GPIO_ECHO_PIN, 1);
+		}
 		pps_event(info->pps, &ts, PPS_CAPTUREASSERT, NULL);
-	else if (info->capture_clear &&
+	} else if (info->capture_clear &&
 			((rising_edge && info->assert_falling_edge) ||
-			 (!rising_edge && !info->assert_falling_edge)))
+			 (!rising_edge && !info->assert_falling_edge))) {
+		if (info->pps->params.mode & PPS_ECHOCLEAR) {
+			gpio_set_value(PPS_GPIO_ECHO_PIN, 1);
+		}
 		pps_event(info->pps, &ts, PPS_CAPTURECLEAR, NULL);
+	}
 
+	if (info->pps->params.mode & (PPS_ECHOASSERT | PPS_ECHOCLEAR))
+		return IRQ_WAKE_THREAD;
 	return IRQ_HANDLED;
 }
 
+/* If we sent an echo pulse, we set the output pin back to low. This results in
+ * an echo pulse of roughly 100ms length.
+ */
+static irqreturn_t pps_gpio_irq_threaded(int irq, void *data)
+{
+	const struct pps_gpio_device_data *info;
+
+	info = data;
+
+	msleep(100);
+	gpio_set_value(PPS_GPIO_ECHO_PIN, 0);
+
+	return IRQ_HANDLED;
+}
+
+
 static unsigned long
 get_irqf_trigger_flags(const struct pps_gpio_device_data *data)
 {
@@ -131,7 +162,20 @@ static int pps_gpio_probe(struct platform_device *pdev)
 
 	ret = gpio_direction_input(data->gpio_pin);
 	if (ret) {
-		dev_err(&pdev->dev, "failed to set pin direction\n");
+		dev_err(&pdev->dev, "failed to set pin as input\n");
+		return -EINVAL;
+	}
+
+	ret = devm_gpio_request(&pdev->dev, PPS_GPIO_ECHO_PIN, gpio_label);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to request GPIO %u\n",
+			PPS_GPIO_ECHO_PIN);
+		return ret;
+	}
+
+	ret = gpio_direction_output(PPS_GPIO_ECHO_PIN, 0);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to set pin as output\n");
 		return -EINVAL;
 	}
 
@@ -165,7 +209,8 @@ static int pps_gpio_probe(struct platform_device *pdev)
 	}
 
 	/* register IRQ interrupt handler */
-	ret = devm_request_irq(&pdev->dev, data->irq, pps_gpio_irq_handler,
+	ret = devm_request_threaded_irq(&pdev->dev, data->irq,
+			pps_gpio_irq_handler, pps_gpio_irq_threaded,
 			get_irqf_trigger_flags(data), data->info.name, data);
 	if (ret) {
 		pps_unregister_source(data->pps);
-- 
2.16.1