staging:iio:ad7606: Factor out common code between periodic and one-shot capture

Both the periodic buffer based and one-shot sysfs based capture methods
share a large portion of their code. Factor this out into a common helper
function.

Also provide a comment that better explains in more detail what is going on
in the capture function.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/adc/ad7606.h

@@ -84,6 +84,7 @@ struct iio_dev *ad7606_probe(struct device *dev, int irq,
 			      const struct ad7606_bus_ops *bops);
 int ad7606_remove(struct iio_dev *indio_dev, int irq);
 int ad7606_reset(struct ad7606_state *st);
+int ad7606_read_samples(struct ad7606_state *st);
 
 enum ad7606_supported_device_ids {
 	ID_AD7606_8,

drivers/staging/iio/adc/ad7606_core.c

@@ -36,39 +36,53 @@ int ad7606_reset(struct ad7606_state *st)
 	return -ENODEV;
 }
 
-static int ad7606_scan_direct(struct iio_dev *indio_dev, unsigned int ch)
+int ad7606_read_samples(struct ad7606_state *st)
 {
-	struct ad7606_state *st = iio_priv(indio_dev);
+	unsigned int num = st->chip_info->num_channels;
+	u16 *data = st->data;
 	int ret;
 
-	st->done = false;
-	gpio_set_value(st->pdata->gpio_convst, 1);
-
-	ret = wait_event_interruptible(st->wq_data_avail, st->done);
-	if (ret)
-		goto error_ret;
+	/*
+	 * The frstdata signal is set to high while and after reading the sample
+	 * of the first channel and low for all other channels. This can be used
+	 * to check that the incoming data is correctly aligned. During normal
+	 * operation the data should never become unaligned, but some glitch or
+	 * electrostatic discharge might cause an extra read or clock cycle.
+	 * Monitoring the frstdata signal allows to recover from such failure
+	 * situations.
+	 */
 
 	if (gpio_is_valid(st->pdata->gpio_frstdata)) {
-		ret = st->bops->read_block(st->dev, 1, st->data);
+		ret = st->bops->read_block(st->dev, 1, data);
 		if (ret)
-			goto error_ret;
+			return ret;
+
 		if (!gpio_get_value(st->pdata->gpio_frstdata)) {
-			/* This should never happen */
 			ad7606_reset(st);
-			ret = -EIO;
-			goto error_ret;
+			return -EIO;
 		}
-		ret = st->bops->read_block(st->dev,
-			st->chip_info->num_channels - 1, &st->data[1]);
-		if (ret)
-			goto error_ret;
-	} else {
-		ret = st->bops->read_block(st->dev,
-			st->chip_info->num_channels, st->data);
+
+		data++;
+		num--;
+	}
+
+	return st->bops->read_block(st->dev, num, data);
+}
+
+static int ad7606_scan_direct(struct iio_dev *indio_dev, unsigned int ch)
+{
+	struct ad7606_state *st = iio_priv(indio_dev);
+	int ret;
+
+	st->done = false;
+	gpio_set_value(st->pdata->gpio_convst, 1);
+
+	ret = wait_event_interruptible(st->wq_data_avail, st->done);
 	if (ret)
 		goto error_ret;
-	}
 
+	ret = ad7606_read_samples(st);
+	if (ret == 0)
 		ret = st->data[ch];
 
 error_ret:

drivers/staging/iio/adc/ad7606_ring.c

@@ -48,33 +48,11 @@ static void ad7606_poll_bh_to_ring(struct work_struct *work_s)
 	struct iio_dev *indio_dev = iio_priv_to_dev(st);
 	int ret;
 
-	if (gpio_is_valid(st->pdata->gpio_frstdata)) {
-		ret = st->bops->read_block(st->dev, 1, st->data);
-		if (ret)
-			goto done;
-		if (!gpio_get_value(st->pdata->gpio_frstdata)) {
-			/* This should never happen. However
-			 * some signal glitch caused by bad PCB desgin or
-			 * electrostatic discharge, could cause an extra read
-			 * or clock. This allows recovery.
-			 */
-			ad7606_reset(st);
-			goto done;
-		}
-		ret = st->bops->read_block(st->dev,
-			st->chip_info->num_channels - 1, st->data + 1);
-		if (ret)
-			goto done;
-	} else {
-		ret = st->bops->read_block(st->dev,
-			st->chip_info->num_channels, st->data);
-		if (ret)
-			goto done;
-	}
-
+	ret = ad7606_read_samples(st);
+	if (ret == 0)
 		iio_push_to_buffers_with_timestamp(indio_dev, st->data,
 						   iio_get_time_ns(indio_dev));
-done:
+
 	gpio_set_value(st->pdata->gpio_convst, 0);
 	iio_trigger_notify_done(indio_dev->trig);
 }