staging: iio: adc: Enable driver support for ad7887 AD converter

Enable support for AD7887:  SPI Micropower, 2-Channel, 125 kSPS, 12-Bit ADC

staging: iio: adc: Fix according to review feedback

Review feedback by Jonathan Cameron:
	Combine statements.
	Document struct members.
	Remove redundant variable initialization.
	Simplify multichannel scan from ring logic.
	Fix coding style.

[v2]
staging: iio: adc: ad7887: Fix typos

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

5 files changed, 694 insertions, 0 deletions

diff --git a/drivers/staging/iio/adc/Kconfig b/drivers/staging/iio/adc/Kconfig
index 9ca6565..86869cd 100644
--- a/drivers/staging/iio/adc/Kconfig
+++ b/drivers/staging/iio/adc/Kconfig
@@ -97,6 +97,20 @@ config AD7476
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad7476.
 
+config AD7887
+	tristate "Analog Devices AD7887 ADC driver"
+	depends on SPI
+	select IIO_RING_BUFFER
+	select IIO_SW_RING
+	select IIO_TRIGGER
+	help
+	  Say yes here to build support for Analog Devices
+	  AD7887 SPI analog to digital convertor (ADC).
+	  If unsure, say N (but it's safe to say "Y").
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ad7887.
+
 config AD7745
 	tristate "Analog Devices AD7745, AD7746 AD7747 capacitive sensor driver"
 	depends on I2C
diff --git a/drivers/staging/iio/adc/Makefile b/drivers/staging/iio/adc/Makefile
index a7dce6b..6f231a2 100644
--- a/drivers/staging/iio/adc/Makefile
+++ b/drivers/staging/iio/adc/Makefile
@@ -15,6 +15,10 @@ ad7476-y := ad7476_core.o
 ad7476-$(CONFIG_IIO_RING_BUFFER) += ad7476_ring.o
 obj-$(CONFIG_AD7476) += ad7476.o
 
+ad7887-y := ad7887_core.o
+ad7887-$(CONFIG_IIO_RING_BUFFER) += ad7887_ring.o
+obj-$(CONFIG_AD7887) += ad7887.o
+
 obj-$(CONFIG_AD7150) += ad7150.o
 obj-$(CONFIG_AD7152) += ad7152.o
 obj-$(CONFIG_AD7291) += ad7291.o
diff --git a/drivers/staging/iio/adc/ad7887.h b/drivers/staging/iio/adc/ad7887.h
new file mode 100644
index 0000000..8c2a218
--- /dev/null
+++ b/drivers/staging/iio/adc/ad7887.h
@@ -0,0 +1,105 @@
+/*
+ * AD7887 SPI ADC driver
+ *
+ * Copyright 2010 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2 or later.
+ */
+#ifndef IIO_ADC_AD7887_H_
+#define IIO_ADC_AD7887_H_
+
+#define AD7887_REF_DIS		(1 << 5) /* on-chip reference disable */
+#define AD7887_DUAL		(1 << 4) /* dual-channel mode */
+#define AD7887_CH_AIN1		(1 << 3) /* convert on channel 1, DUAL=1 */
+#define AD7887_CH_AIN0		(0 << 3) /* convert on channel 0, DUAL=0,1 */
+#define AD7887_PM_MODE1		(0)	 /* CS based shutdown */
+#define AD7887_PM_MODE2		(1)	 /* full on */
+#define AD7887_PM_MODE3		(2)	 /* auto shutdown after conversion */
+#define AD7887_PM_MODE4		(3)	 /* standby mode */
+
+enum ad7887_channels {
+	AD7887_CH0,
+	AD7887_CH0_CH1,
+	AD7887_CH1,
+};
+
+#define RES_MASK(bits)	((1 << (bits)) - 1) /* TODO: move this into a common header */
+
+/*
+ * TODO: struct ad7887_platform_data needs to go into include/linux/iio
+ */
+
+struct ad7887_platform_data {
+	/* External Vref voltage applied */
+	u16				vref_mv;
+	/*
+	 * AD7887:
+	 * In single channel mode en_dual = flase, AIN1/Vref pins assumes its
+	 * Vref function. In dual channel mode en_dual = true, AIN1 becomes the
+	 * second input channel, and Vref is internally connected to Vdd.
+	 */
+	bool				en_dual;
+	/*
+	 * AD7887:
+	 * use_onchip_ref = true, the Vref is internally connected to the 2.500V
+	 * Voltage reference. If use_onchip_ref = false, the reference voltage
+	 * is supplied by AIN1/Vref
+	 */
+	bool				use_onchip_ref;
+};
+
+struct ad7887_chip_info {
+	u8				bits;		/* number of ADC bits */
+	u8				storagebits;	/* number of bits read from the ADC */
+	u8				left_shift;	/* number of bits the sample must be shifted */
+	char				sign;		/* [s]igned or [u]nsigned */
+	u16				int_vref_mv;	/* internal reference voltage */
+};
+
+struct ad7887_state {
+	struct iio_dev			*indio_dev;
+	struct spi_device		*spi;
+	const struct ad7887_chip_info	*chip_info;
+	struct regulator		*reg;
+	struct work_struct		poll_work;
+	atomic_t			protect_ring;
+	u16				int_vref_mv;
+	bool				en_dual;
+	struct spi_transfer		xfer[4];
+	struct spi_message		msg[3];
+	struct spi_message		*ring_msg;
+	unsigned char			tx_cmd_buf[8];
+
+	/*
+	 * DMA (thus cache coherency maintenance) requires the
+	 * transfer buffers to live in their own cache lines.
+	 */
+
+	unsigned char			data[4] ____cacheline_aligned;
+};
+
+enum ad7887_supported_device_ids {
+	ID_AD7887
+};
+
+#ifdef CONFIG_IIO_RING_BUFFER
+int ad7887_scan_from_ring(struct ad7887_state *st, long mask);
+int ad7887_register_ring_funcs_and_init(struct iio_dev *indio_dev);
+void ad7887_ring_cleanup(struct iio_dev *indio_dev);
+#else /* CONFIG_IIO_RING_BUFFER */
+static inline int ad7887_scan_from_ring(struct ad7887_state *st, long mask)
+{
+	return 0;
+}
+
+static inline int
+ad7887_register_ring_funcs_and_init(struct iio_dev *indio_dev)
+{
+	return 0;
+}
+
+static inline void ad7887_ring_cleanup(struct iio_dev *indio_dev)
+{
+}
+#endif /* CONFIG_IIO_RING_BUFFER */
+#endif /* IIO_ADC_AD7887_H_ */
diff --git a/drivers/staging/iio/adc/ad7887_core.c b/drivers/staging/iio/adc/ad7887_core.c
new file mode 100644
index 0000000..6859089
--- /dev/null
+++ b/drivers/staging/iio/adc/ad7887_core.c
@@ -0,0 +1,305 @@
+/*
+ * AD7887 SPI ADC driver
+ *
+ * Copyright 2010 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2 or later.
+ */
+
+#include <linux/interrupt.h>
+#include <linux/workqueue.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+#include <linux/list.h>
+#include <linux/spi/spi.h>
+#include <linux/regulator/consumer.h>
+#include <linux/err.h>
+
+#include "../iio.h"
+#include "../sysfs.h"
+#include "../ring_generic.h"
+#include "adc.h"
+
+#include "ad7887.h"
+
+static int ad7887_scan_direct(struct ad7887_state *st, unsigned ch)
+{
+	int ret = spi_sync(st->spi, &st->msg[ch]);
+	if (ret)
+		return ret;
+
+	return (st->data[(ch * 2)] << 8) | st->data[(ch * 2) + 1];
+}
+
+static ssize_t ad7887_scan(struct device *dev,
+			    struct device_attribute *attr,
+			    char *buf)
+{
+	struct iio_dev *dev_info = dev_get_drvdata(dev);
+	struct ad7887_state *st = dev_info->dev_data;
+	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+	int ret;
+
+	mutex_lock(&dev_info->mlock);
+	if (iio_ring_enabled(dev_info))
+		ret = ad7887_scan_from_ring(st, 1 << this_attr->address);
+	else
+		ret = ad7887_scan_direct(st, this_attr->address);
+	mutex_unlock(&dev_info->mlock);
+
+	if (ret < 0)
+		return ret;
+
+	return sprintf(buf, "%d\n", (ret >> st->chip_info->left_shift) &
+		       RES_MASK(st->chip_info->bits));
+}
+static IIO_DEV_ATTR_IN_RAW(0, ad7887_scan, 0);
+static IIO_DEV_ATTR_IN_RAW(1, ad7887_scan, 1);
+
+static ssize_t ad7887_show_scale(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	/* Driver currently only support internal vref */
+	struct iio_dev *dev_info = dev_get_drvdata(dev);
+	struct ad7887_state *st = iio_dev_get_devdata(dev_info);
+	/* Corresponds to Vref / 2^(bits) */
+	unsigned int scale_uv = (st->int_vref_mv * 1000) >> st->chip_info->bits;
+
+	return sprintf(buf, "%d.%d\n", scale_uv / 1000, scale_uv % 1000);
+}
+static IIO_DEVICE_ATTR(in_scale, S_IRUGO, ad7887_show_scale, NULL, 0);
+
+static ssize_t ad7887_show_name(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct iio_dev *dev_info = dev_get_drvdata(dev);
+	struct ad7887_state *st = iio_dev_get_devdata(dev_info);
+
+	return sprintf(buf, "%s\n", spi_get_device_id(st->spi)->name);
+}
+static IIO_DEVICE_ATTR(name, S_IRUGO, ad7887_show_name, NULL, 0);
+
+static struct attribute *ad7887_attributes[] = {
+	&iio_dev_attr_in0_raw.dev_attr.attr,
+	&iio_dev_attr_in1_raw.dev_attr.attr,
+	&iio_dev_attr_in_scale.dev_attr.attr,
+	&iio_dev_attr_name.dev_attr.attr,
+	NULL,
+};
+
+static mode_t ad7887_attr_is_visible(struct kobject *kobj,
+				     struct attribute *attr, int n)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct iio_dev *dev_info = dev_get_drvdata(dev);
+	struct ad7887_state *st = iio_dev_get_devdata(dev_info);
+
+	mode_t mode = attr->mode;
+
+	if ((attr == &iio_dev_attr_in1_raw.dev_attr.attr) && !st->en_dual)
+			mode = 0;
+
+	return mode;
+}
+
+static const struct attribute_group ad7887_attribute_group = {
+	.attrs = ad7887_attributes,
+	.is_visible = ad7887_attr_is_visible,
+};
+
+static const struct ad7887_chip_info ad7887_chip_info_tbl[] = {
+	/*
+	 * More devices added in future
+	 */
+	[ID_AD7887] = {
+		.bits = 12,
+		.storagebits = 16,
+		.left_shift = 0,
+		.sign = IIO_SCAN_EL_TYPE_UNSIGNED,
+		.int_vref_mv = 2500,
+	},
+};
+
+static int __devinit ad7887_probe(struct spi_device *spi)
+{
+	struct ad7887_platform_data *pdata = spi->dev.platform_data;
+	struct ad7887_state *st;
+	int ret, voltage_uv = 0;
+
+	st = kzalloc(sizeof(*st), GFP_KERNEL);
+	if (st == NULL) {
+		ret = -ENOMEM;
+		goto error_ret;
+	}
+
+	st->reg = regulator_get(&spi->dev, "vcc");
+	if (!IS_ERR(st->reg)) {
+		ret = regulator_enable(st->reg);
+		if (ret)
+			goto error_put_reg;
+
+		voltage_uv = regulator_get_voltage(st->reg);
+	}
+
+	st->chip_info =
+		&ad7887_chip_info_tbl[spi_get_device_id(spi)->driver_data];
+
+	spi_set_drvdata(spi, st);
+
+	atomic_set(&st->protect_ring, 0);
+	st->spi = spi;
+
+	st->indio_dev = iio_allocate_device();
+	if (st->indio_dev == NULL) {
+		ret = -ENOMEM;
+		goto error_disable_reg;
+	}
+
+	/* Estabilish that the iio_dev is a child of the spi device */
+	st->indio_dev->dev.parent = &spi->dev;
+	st->indio_dev->attrs = &ad7887_attribute_group;
+	st->indio_dev->dev_data = (void *)(st);
+	st->indio_dev->driver_module = THIS_MODULE;
+	st->indio_dev->modes = INDIO_DIRECT_MODE;
+
+	/* Setup default message */
+
+	st->tx_cmd_buf[0] = AD7887_CH_AIN0 | AD7887_PM_MODE4 |
+			    ((pdata && pdata->use_onchip_ref) ?
+			    0 : AD7887_REF_DIS);
+
+	st->xfer[0].rx_buf = &st->data[0];
+	st->xfer[0].tx_buf = &st->tx_cmd_buf[0];
+	st->xfer[0].len = 2;
+
+	spi_message_init(&st->msg[AD7887_CH0]);
+	spi_message_add_tail(&st->xfer[0], &st->msg[AD7887_CH0]);
+
+	if (pdata && pdata->en_dual) {
+		st->tx_cmd_buf[0] |= AD7887_DUAL | AD7887_REF_DIS;
+
+		st->tx_cmd_buf[2] = AD7887_CH_AIN1 | AD7887_DUAL |
+				    AD7887_REF_DIS | AD7887_PM_MODE4;
+		st->tx_cmd_buf[4] = AD7887_CH_AIN0 | AD7887_DUAL |
+				    AD7887_REF_DIS | AD7887_PM_MODE4;
+		st->tx_cmd_buf[6] = AD7887_CH_AIN1 | AD7887_DUAL |
+				    AD7887_REF_DIS | AD7887_PM_MODE4;
+
+		st->xfer[1].rx_buf = &st->data[0];
+		st->xfer[1].tx_buf = &st->tx_cmd_buf[2];
+		st->xfer[1].len = 2;
+
+		st->xfer[2].rx_buf = &st->data[2];
+		st->xfer[2].tx_buf = &st->tx_cmd_buf[4];
+		st->xfer[2].len = 2;
+
+		spi_message_init(&st->msg[AD7887_CH0_CH1]);
+		spi_message_add_tail(&st->xfer[1], &st->msg[AD7887_CH0_CH1]);
+		spi_message_add_tail(&st->xfer[2], &st->msg[AD7887_CH0_CH1]);
+
+		st->xfer[3].rx_buf = &st->data[0];
+		st->xfer[3].tx_buf = &st->tx_cmd_buf[6];
+		st->xfer[3].len = 2;
+
+		spi_message_init(&st->msg[AD7887_CH1]);
+		spi_message_add_tail(&st->xfer[3], &st->msg[AD7887_CH1]);
+
+		st->en_dual = true;
+
+		if (pdata && pdata->vref_mv)
+			st->int_vref_mv = pdata->vref_mv;
+		else if (voltage_uv)
+			st->int_vref_mv = voltage_uv / 1000;
+		else
+			dev_warn(&spi->dev, "reference voltage unspecified\n");
+
+	} else {
+		if (pdata && pdata->vref_mv)
+			st->int_vref_mv = pdata->vref_mv;
+		else if (pdata && pdata->use_onchip_ref)
+			st->int_vref_mv = st->chip_info->int_vref_mv;
+		else
+			dev_warn(&spi->dev, "reference voltage unspecified\n");
+	}
+
+
+	ret = ad7887_register_ring_funcs_and_init(st->indio_dev);
+	if (ret)
+		goto error_free_device;
+
+	ret = iio_device_register(st->indio_dev);
+	if (ret)
+		goto error_free_device;
+
+	ret = iio_ring_buffer_register(st->indio_dev->ring, 0);
+	if (ret)
+		goto error_cleanup_ring;
+	return 0;
+
+error_cleanup_ring:
+	ad7887_ring_cleanup(st->indio_dev);
+	iio_device_unregister(st->indio_dev);
+error_free_device:
+	iio_free_device(st->indio_dev);
+error_disable_reg:
+	if (!IS_ERR(st->reg))
+		regulator_disable(st->reg);
+error_put_reg:
+	if (!IS_ERR(st->reg))
+		regulator_put(st->reg);
+	kfree(st);
+error_ret:
+	return ret;
+}
+
+static int ad7887_remove(struct spi_device *spi)
+{
+	struct ad7887_state *st = spi_get_drvdata(spi);
+	struct iio_dev *indio_dev = st->indio_dev;
+	iio_ring_buffer_unregister(indio_dev->ring);
+	ad7887_ring_cleanup(indio_dev);
+	iio_device_unregister(indio_dev);
+	if (!IS_ERR(st->reg)) {
+		regulator_disable(st->reg);
+		regulator_put(st->reg);
+	}
+	kfree(st);
+	return 0;
+}
+
+static const struct spi_device_id ad7887_id[] = {
+	{"ad7887", ID_AD7887},
+	{}
+};
+
+static struct spi_driver ad7887_driver = {
+	.driver = {
+		.name	= "ad7887",
+		.bus	= &spi_bus_type,
+		.owner	= THIS_MODULE,
+	},
+	.probe		= ad7887_probe,
+	.remove		= __devexit_p(ad7887_remove),
+	.id_table	= ad7887_id,
+};
+
+static int __init ad7887_init(void)
+{
+	return spi_register_driver(&ad7887_driver);
+}
+module_init(ad7887_init);
+
+static void __exit ad7887_exit(void)
+{
+	spi_unregister_driver(&ad7887_driver);
+}
+module_exit(ad7887_exit);
+
+MODULE_AUTHOR("Michael Hennerich <hennerich@blackfin.uclinux.org>");
+MODULE_DESCRIPTION("Analog Devices AD7887 ADC");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("spi:ad7887");
diff --git a/drivers/staging/iio/adc/ad7887_ring.c b/drivers/staging/iio/adc/ad7887_ring.c
new file mode 100644
index 0000000..6b9cb1f
--- /dev/null
+++ b/drivers/staging/iio/adc/ad7887_ring.c
@@ -0,0 +1,266 @@
+/*
+ * Copyright 2010 Analog Devices Inc.
+ * Copyright (C) 2008 Jonathan Cameron
+ *
+ * Licensed under the GPL-2 or later.
+ *
+ * ad7887_ring.c
+ */
+
+#include <linux/interrupt.h>
+#include <linux/gpio.h>
+#include <linux/workqueue.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+#include <linux/list.h>
+#include <linux/spi/spi.h>
+
+#include "../iio.h"
+#include "../ring_generic.h"
+#include "../ring_sw.h"
+#include "../trigger.h"
+#include "../sysfs.h"
+
+#include "ad7887.h"
+
+static IIO_SCAN_EL_C(in0, 0, 0, NULL);
+static IIO_SCAN_EL_C(in1, 1, 0, NULL);
+
+static ssize_t ad7887_show_type(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct iio_ring_buffer *ring = dev_get_drvdata(dev);
+	struct iio_dev *indio_dev = ring->indio_dev;
+	struct ad7887_state *st = indio_dev->dev_data;
+
+	return sprintf(buf, "%c%d/%d>>%d\n", st->chip_info->sign,
+		       st->chip_info->bits, st->chip_info->storagebits,
+		       st->chip_info->left_shift);
+}
+static IIO_DEVICE_ATTR(in_type, S_IRUGO, ad7887_show_type, NULL, 0);
+
+static struct attribute *ad7887_scan_el_attrs[] = {
+	&iio_scan_el_in0.dev_attr.attr,
+	&iio_const_attr_in0_index.dev_attr.attr,
+	&iio_scan_el_in1.dev_attr.attr,
+	&iio_const_attr_in1_index.dev_attr.attr,
+	&iio_dev_attr_in_type.dev_attr.attr,
+	NULL,
+};
+
+static mode_t ad7887_scan_el_attr_is_visible(struct kobject *kobj,
+				     struct attribute *attr, int n)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct iio_ring_buffer *ring = dev_get_drvdata(dev);
+	struct iio_dev *indio_dev = ring->indio_dev;
+	struct ad7887_state *st = indio_dev->dev_data;
+
+	mode_t mode = attr->mode;
+
+	if ((attr == &iio_scan_el_in1.dev_attr.attr) ||
+		(attr == &iio_const_attr_in1_index.dev_attr.attr))
+		if (!st->en_dual)
+			mode = 0;
+
+	return mode;
+}
+
+static struct attribute_group ad7887_scan_el_group = {
+	.name = "scan_elements",
+	.attrs = ad7887_scan_el_attrs,
+	.is_visible = ad7887_scan_el_attr_is_visible,
+};
+
+int ad7887_scan_from_ring(struct ad7887_state *st, long mask)
+{
+	struct iio_ring_buffer *ring = st->indio_dev->ring;
+	int count = 0, ret;
+	u16 *ring_data;
+
+	if (!(ring->scan_mask & mask)) {
+		ret = -EBUSY;
+		goto error_ret;
+	}
+
+	ring_data = kmalloc(ring->access.get_bytes_per_datum(ring), GFP_KERNEL);
+	if (ring_data == NULL) {
+		ret = -ENOMEM;
+		goto error_ret;
+	}
+	ret = ring->access.read_last(ring, (u8 *) ring_data);
+	if (ret)
+		goto error_free_ring_data;
+
+	/* for single channel scan the result is stored with zero offset */
+	if ((ring->scan_mask == ((1 << 1) | (1 << 0))) && (mask == (1 << 1)))
+		count = 1;
+
+	ret = be16_to_cpu(ring_data[count]);
+
+error_free_ring_data:
+	kfree(ring_data);
+error_ret:
+	return ret;
+}
+
+/**
+ * ad7887_ring_preenable() setup the parameters of the ring before enabling
+ *
+ * The complex nature of the setting of the nuber of bytes per datum is due
+ * to this driver currently ensuring that the timestamp is stored at an 8
+ * byte boundary.
+ **/
+static int ad7887_ring_preenable(struct iio_dev *indio_dev)
+{
+	struct ad7887_state *st = indio_dev->dev_data;
+	struct iio_ring_buffer *ring = indio_dev->ring;
+	size_t d_size;
+
+	if (indio_dev->ring->access.set_bytes_per_datum) {
+		d_size = st->chip_info->storagebits / 8 + sizeof(s64);
+		if (d_size % 8)
+			d_size += 8 - (d_size % 8);
+		indio_dev->ring->access.set_bytes_per_datum(indio_dev->ring,
+							    d_size);
+	}
+
+	switch (ring->scan_mask) {
+	case (1 << 0):
+		st->ring_msg = &st->msg[AD7887_CH0];
+		break;
+	case (1 << 1):
+		st->ring_msg = &st->msg[AD7887_CH1];
+		/* Dummy read: push CH1 setting down to hardware */
+		spi_sync(st->spi, st->ring_msg);
+		break;
+	case ((1 << 1) | (1 << 0)):
+		st->ring_msg = &st->msg[AD7887_CH0_CH1];
+		break;
+	}
+
+	return 0;
+}
+
+static int ad7887_ring_postdisable(struct iio_dev *indio_dev)
+{
+	struct ad7887_state *st = indio_dev->dev_data;
+
+	/* dummy read: restore default CH0 settin */
+	return spi_sync(st->spi, &st->msg[AD7887_CH0]);
+}
+
+/**
+ * ad7887_poll_func_th() th of trigger launched polling to ring buffer
+ *
+ * As sampling only occurs on spi comms occuring, leave timestamping until
+ * then.  Some triggers will generate their own time stamp.  Currently
+ * there is no way of notifying them when no one cares.
+ **/
+static void ad7887_poll_func_th(struct iio_dev *indio_dev, s64 time)
+{
+	struct ad7887_state *st = indio_dev->dev_data;
+
+	schedule_work(&st->poll_work);
+	return;
+}
+/**
+ * ad7887_poll_bh_to_ring() bh of trigger launched polling to ring buffer
+ * @work_s:	the work struct through which this was scheduled
+ *
+ * Currently there is no option in this driver to disable the saving of
+ * timestamps within the ring.
+ * I think the one copy of this at a time was to avoid problems if the
+ * trigger was set far too high and the reads then locked up the computer.
+ **/
+static void ad7887_poll_bh_to_ring(struct work_struct *work_s)
+{
+	struct ad7887_state *st = container_of(work_s, struct ad7887_state,
+						  poll_work);
+	struct iio_dev *indio_dev = st->indio_dev;
+	struct iio_sw_ring_buffer *sw_ring = iio_to_sw_ring(indio_dev->ring);
+	struct iio_ring_buffer *ring = indio_dev->ring;
+	s64 time_ns;
+	__u8 *buf;
+	int b_sent;
+	size_t d_size;
+
+	unsigned int bytes = ring->scan_count * st->chip_info->storagebits / 8;
+
+	/* Ensure the timestamp is 8 byte aligned */
+	d_size = bytes + sizeof(s64);
+	if (d_size % sizeof(s64))
+		d_size += sizeof(s64) - (d_size % sizeof(s64));
+
+	/* Ensure only one copy of this function running at a time */
+	if (atomic_inc_return(&st->protect_ring) > 1)
+		return;
+
+	buf = kzalloc(d_size, GFP_KERNEL);
+	if (buf == NULL)
+		return;
+
+	b_sent = spi_sync(st->spi, st->ring_msg);
+	if (b_sent)
+		goto done;
+
+	time_ns = iio_get_time_ns();
+
+	memcpy(buf, st->data, bytes);
+	memcpy(buf + d_size - sizeof(s64), &time_ns, sizeof(time_ns));
+
+	indio_dev->ring->access.store_to(&sw_ring->buf, buf, time_ns);
+done:
+	kfree(buf);
+	atomic_dec(&st->protect_ring);
+}
+
+int ad7887_register_ring_funcs_and_init(struct iio_dev *indio_dev)
+{
+	struct ad7887_state *st = indio_dev->dev_data;
+	int ret;
+
+	indio_dev->ring = iio_sw_rb_allocate(indio_dev);
+	if (!indio_dev->ring) {
+		ret = -ENOMEM;
+		goto error_ret;
+	}
+	/* Effectively select the ring buffer implementation */
+	iio_ring_sw_register_funcs(&indio_dev->ring->access);
+	ret = iio_alloc_pollfunc(indio_dev, NULL, &ad7887_poll_func_th);
+	if (ret)
+		goto error_deallocate_sw_rb;
+
+	/* Ring buffer functions - here trigger setup related */
+
+	indio_dev->ring->preenable = &ad7887_ring_preenable;
+	indio_dev->ring->postenable = &iio_triggered_ring_postenable;
+	indio_dev->ring->predisable = &iio_triggered_ring_predisable;
+	indio_dev->ring->postdisable = &ad7887_ring_postdisable;
+	indio_dev->ring->scan_el_attrs = &ad7887_scan_el_group;
+
+	INIT_WORK(&st->poll_work, &ad7887_poll_bh_to_ring);
+
+	/* Flag that polled ring buffering is possible */
+	indio_dev->modes |= INDIO_RING_TRIGGERED;
+	return 0;
+error_deallocate_sw_rb:
+	iio_sw_rb_free(indio_dev->ring);
+error_ret:
+	return ret;
+}
+
+void ad7887_ring_cleanup(struct iio_dev *indio_dev)
+{
+	/* ensure that the trigger has been detached */
+	if (indio_dev->trig) {
+		iio_put_trigger(indio_dev->trig);
+		iio_trigger_dettach_poll_func(indio_dev->trig,
+					      indio_dev->pollfunc);
+	}
+	kfree(indio_dev->pollfunc);
+	iio_sw_rb_free(indio_dev->ring);
+}