[PATCH v2 2/2] iio: ina2xx: provide a sysfs parameter to allow async readout of the ADCs

[Marc Titinger <mtitinger@baylibre.com>]

This can lead to repeated or skipped samples depending on the clock beat
between the capture thread and the chip sampling clock, but will also spare
reading/waiting for the Capture Ready Flag and improve the available i2c
bandwidth for reading measurements.

Output of iio_info:
...snip...
4 device-specific attributes found:
  attr 0: in_oversampling_ratio value: 4
  attr 1: in_allow_async_readout value: 0
  attr 2: integration_time_available value: 140 204 332 588 1100 2116 4156 8244
  attr 3: in_sampling_frequency value: 114

Signed-off-by: Marc Titinger <mtitinger@baylibre.com>
---
 drivers/iio/adc/ina2xx-iio.c | 48 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/adc/ina2xx-iio.c b/drivers/iio/adc/ina2xx-iio.c
index 99fb73c..7575a12 100644
--- a/drivers/iio/adc/ina2xx-iio.c
+++ b/drivers/iio/adc/ina2xx-iio.c
@@ -117,6 +117,7 @@ struct ina2xx_chip_info {
 	s64 prev_ns;	/* track buffer capture time check, for underruns*/
 	int int_time_vbus; /* Bus voltage integration time uS */
 	int int_time_vshunt; /* Shunt voltage integration time uS */
+	bool allow_async_readout;
 };
 
 static const struct ina2xx_config ina2xx_config[] = {
@@ -333,6 +334,33 @@ _err:
 }
 
 
+static ssize_t ina2xx_allow_async_readout_show(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	struct ina2xx_chip_info *chip = iio_priv(dev_to_iio_dev(dev));
+
+	return sprintf(buf, "%d\n", chip->allow_async_readout);
+}
+
+static ssize_t ina2xx_allow_async_readout_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t len)
+{
+	struct ina2xx_chip_info *chip = iio_priv(dev_to_iio_dev(dev));
+	bool val;
+	int ret;
+
+	ret = strtobool((const char *) buf, &val);
+	if (ret)
+		return ret;
+
+	chip->allow_async_readout = val;
+
+	return len;
+}
+
+
 #define INA2XX_CHAN(_type, _index, _address) { \
 	.type = _type, \
 	.address = _address, \
@@ -399,11 +427,12 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev)
 	 * GPIO a triggered buffer could be used instead.
 	 * For now, we pay for that extra read of the ALERT register
 	 */
-	do {
-		ret = regmap_read(chip->regmap, INA226_ALERT_MASK,
-				  &alert);
-		if (ret < 0)
-			goto _err;
+	if (!chip->allow_async_readout)
+		do {
+			ret = regmap_read(chip->regmap, INA226_ALERT_MASK,
+					  &alert);
+			if (ret < 0)
+				goto _err;
 
 		alert &= INA266_CVRF;
 		trace_printk("Conversion ready: %d\n", !!alert);
@@ -454,7 +483,8 @@ static int ina2xx_capture_thread(void *data)
 	 * Poll a bit faster than the chip internal Fs, in case
 	 * we wish to sync with the conversion ready flag.
 	 */
-	sampling_us -= 200;
+	if (!chip->allow_async_readout)
+		sampling_us -= 200;
 
 	do {
 		buffer_us = ina2xx_work_buffer(indio_dev);
@@ -477,6 +507,7 @@ int ina2xx_buffer_enable(struct iio_dev *indio_dev)
 		     1000000/sampling_us, chip->avg);
 
 	trace_printk("Expected work period: %u us\n", sampling_us);
+	trace_printk("Async readout mode: %d\n", chip->allow_async_readout);
 
 	chip->prev_ns = iio_get_time_ns();
 
@@ -518,7 +549,12 @@ static int ina2xx_debug_reg(struct iio_dev *indio_dev,
 static IIO_CONST_ATTR_INT_TIME_AVAIL \
  ("0.000140 0.000204 0.000332 0.000588 0.001100 0.002116 0.004156 0.008244");
 
+static IIO_DEVICE_ATTR(in_allow_async_readout, S_IRUGO | S_IWUSR,
+		       ina2xx_allow_async_readout_show,
+		       ina2xx_allow_async_readout_store, 0);
+
 static struct attribute *ina2xx_attributes[] = {
+	&iio_dev_attr_in_allow_async_readout.dev_attr.attr,
 	&iio_const_attr_integration_time_available.dev_attr.attr,
 	NULL,
 };
-- 
1.9.1