iio: imu: adis: Refactor adis_initial_startup

All the ADIS devices perform, at the beginning, a self test to make sure
the device is in a sane state. Previously, the logic was that the self-test
was performed in adis_initial_startup() and if that failed a reset was done
and then a self-test was attempted again.

This change unifies the reset mechanism under the adis_initial_startup()
call. A HW reset will be done if  GPIO is configured, or a SW reset
otherwise. This should make sure that the chip is in a sane state for
self-test. Once the reset is done, the self-test operation will be
performed. If anything goes wrong with self-test, the driver should just
bail/error-out (i.e. no second attempt). The chip would likely not be a in
a sane state state if the self-test fails after a reset.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/adis.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/mutex.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
@@ -368,6 +369,10 @@ static int adis_self_test(struct adis *adis)
  * __adis_initial_startup() - Device initial setup
  * @adis: The adis device
  *
+ * The function performs a HW reset via a reset pin that should be specified
+ * via GPIOLIB. If no pin is configured a SW reset will be performed.
+ * The RST pin for the ADIS devices should be configured as ACTIVE_LOW.
+ *
  * Returns 0 if the device is operational, a negative error code otherwise.
  *
  * This function should be called early on in the device initialization sequence
@@ -375,18 +380,28 @@ static int adis_self_test(struct adis *adis)
  */
 int __adis_initial_startup(struct adis *adis)
 {
+	const struct adis_timeout *timeouts = adis->data->timeouts;
+	struct gpio_desc *gpio;
 	int ret;
 
-	ret = adis_self_test(adis);
-	if (ret) {
-		dev_err(&adis->spi->dev, "Self-test failed, trying reset.\n");
-		__adis_reset(adis);
-		ret = adis_self_test(adis);
+	/* check if the device has rst pin low */
+	gpio = devm_gpiod_get_optional(&adis->spi->dev, "reset", GPIOD_ASIS);
+	if (IS_ERR(gpio))
+		return PTR_ERR(gpio);
+
+	if (gpio) {
+		gpiod_set_value_cansleep(gpio, 1);
+		msleep(10);
+		/* bring device out of reset */
+		gpiod_set_value_cansleep(gpio, 0);
+		msleep(timeouts->reset_ms);
+	} else {
+		ret = __adis_reset(adis);
 		if (ret)
-			dev_err(&adis->spi->dev, "Second self-test failed, giving up.\n");
+			return ret;
 	}
 
-	return ret;
+	return adis_self_test(adis);
 }
 EXPORT_SYMBOL_GPL(__adis_initial_startup);