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

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Message-Id: <1448884155-2546-3-git-send-email-mtitinger@baylibre.com>
Date:	Mon, 30 Nov 2015 12:49:15 +0100
From:	Marc Titinger <mtitinger@...libre.com>
To:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	pmeerw@...erw.net
Cc:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marc Titinger <mtitinger@...libre.com>
Subject: [PATCH v2 2/2] iio: ina2xx: provide a sysfs parameter to allow async readout of the ADCs

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@...libre.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

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