iio: accel: kxsd9: Add triggered buffer handling

As is custom with all modern sensors, add a clever burst mode
that will just stream out values from the sensor and provide it
to userspace to do the proper offsetting and scaling.

This is the result when tested with an HRTimer trigger:

$ generic_buffer -a -c 10 -n kxsd9 -t foo
/sys/bus/iio/devices/iio:device1 foo
0.371318 0.718680 9.869872 1795.000000 97545896129
-0.586922 0.179670 9.378775 2398.000000 97555864721
-0.299450 0.179670 10.348992 2672.000000 97565874055
0.371318 0.335384 11.103606 2816.000000 97575883240
0.179670 0.574944 10.540640 2847.000000 97585862351
0.335384 0.754614 9.953718 2840.000000 97595872425
0.179670 0.754614 10.732288 2879.000000 97605882351
0.000000 0.754614 10.348992 2872.000000 97615891832
-0.730658 0.574944 9.570422 2831.000000 97625871536
0.000000 1.137910 10.732288 2872.000000 97635881610

Columns shown are x, y, z acceleration, so a positive acceleration
of ~9.81 (shaky due to bad calibration) along the z axis. The
fourth column is the AUX IN which is floating on this system,
it seems to float up to the 2.85V VDD voltage.

To be able to cleanup the triggered buffer, we need to add .remove()
callbacks to the I2C and SPI subdrivers and call back into an
exported .remove() callback in the core.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/accel/Kconfig

@@ -119,6 +119,8 @@ config IIO_ST_ACCEL_SPI_3AXIS
 
 config KXSD9
 	tristate "Kionix KXSD9 Accelerometer Driver"
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
 	help
 	  Say yes here to build support for the Kionix KXSD9 accelerometer.
 	  It can be accessed using an (optional) SPI or I2C interface.

drivers/iio/accel/kxsd9.c

@@ -12,8 +12,6 @@
  * I have a suitable wire made up.
  *
  * TODO:	Support the motion detector
- *		Uses register address incrementing so could have a
- *		heavily optimized ring buffer access function.
  */
 
 #include <linux/device.h>
@@ -24,6 +22,9 @@
 #include <linux/regmap.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
 
 #include "kxsd9.h"
 
@@ -41,9 +42,11 @@
 
 /**
  * struct kxsd9_state - device related storage
+ * @dev: pointer to the parent device
  * @map: regmap to the device
  */
 struct kxsd9_state {
+	struct device *dev;
 	struct regmap *map;
 };
 
@@ -155,7 +158,35 @@ static int kxsd9_read_raw(struct iio_dev *indio_dev,
 error_ret:
 	return ret;
 };
-#define KXSD9_ACCEL_CHAN(axis)						\
+
+static irqreturn_t kxsd9_trigger_handler(int irq, void *p)
+{
+	const struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct kxsd9_state *st = iio_priv(indio_dev);
+	int ret;
+	/* 4 * 16bit values AND timestamp */
+	__be16 hw_values[8];
+
+	ret = regmap_bulk_read(st->map,
+			       KXSD9_REG_X,
+			       &hw_values,
+			       8);
+	if (ret) {
+		dev_err(st->dev,
+			"error reading data\n");
+		return ret;
+	}
+
+	iio_push_to_buffers_with_timestamp(indio_dev,
+					   hw_values,
+					   iio_get_time_ns(indio_dev));
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
+#define KXSD9_ACCEL_CHAN(axis, index)						\
 	{								\
 		.type = IIO_ACCEL,					\
 		.modified = 1,						\
@@ -164,16 +195,35 @@ static int kxsd9_read_raw(struct iio_dev *indio_dev,
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
 					BIT(IIO_CHAN_INFO_OFFSET),	\
 		.address = KXSD9_REG_##axis,				\
+		.scan_index = index,					\
+		.scan_type = {                                          \
+			.sign = 'u',					\
+			.realbits = 12,					\
+			.storagebits = 16,				\
+			.shift = 4,					\
+			.endianness = IIO_BE,				\
+		},							\
 	}
 
 static const struct iio_chan_spec kxsd9_channels[] = {
-	KXSD9_ACCEL_CHAN(X), KXSD9_ACCEL_CHAN(Y), KXSD9_ACCEL_CHAN(Z),
+	KXSD9_ACCEL_CHAN(X, 0),
+	KXSD9_ACCEL_CHAN(Y, 1),
+	KXSD9_ACCEL_CHAN(Z, 2),
 	{
 		.type = IIO_VOLTAGE,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
 		.indexed = 1,
 		.address = KXSD9_REG_AUX,
-	}
+		.scan_index = 3,
+		.scan_type = {
+			.sign = 'u',
+			.realbits = 12,
+			.storagebits = 16,
+			.shift = 4,
+			.endianness = IIO_BE,
+		},
+	},
+	IIO_CHAN_SOFT_TIMESTAMP(4),
 };
 
 static const struct attribute_group kxsd9_attribute_group = {
@@ -197,6 +247,9 @@ static const struct iio_info kxsd9_info = {
 	.driver_module = THIS_MODULE,
 };
 
+/* Four channels apart from timestamp, scan mask = 0x0f */
+static const unsigned long kxsd9_scan_masks[] = { 0xf, 0 };
+
 int kxsd9_common_probe(struct device *parent,
 		       struct regmap *map,
 		       const char *name)
@@ -210,6 +263,7 @@ int kxsd9_common_probe(struct device *parent,
 		return -ENOMEM;
 
 	st = iio_priv(indio_dev);
+	st->dev = parent;
 	st->map = map;
 
 	indio_dev->channels = kxsd9_channels;
@@ -218,16 +272,31 @@ int kxsd9_common_probe(struct device *parent,
 	indio_dev->dev.parent = parent;
 	indio_dev->info = &kxsd9_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->available_scan_masks = kxsd9_scan_masks;
 
 	kxsd9_power_up(st);
 
+	ret = iio_triggered_buffer_setup(indio_dev,
+					 iio_pollfunc_store_time,
+					 kxsd9_trigger_handler,
+					 NULL);
+	if (ret) {
+		dev_err(parent, "triggered buffer setup failed\n");
+		return ret;
+	}
+
 	ret = iio_device_register(indio_dev);
 	if (ret)
-		return ret;
+		goto err_cleanup_buffer;
 
 	dev_set_drvdata(parent, indio_dev);
 
 	return 0;
+
+err_cleanup_buffer:
+	iio_triggered_buffer_cleanup(indio_dev);
+
+	return ret;
 }
 EXPORT_SYMBOL(kxsd9_common_probe);
 
@@ -235,6 +304,7 @@ int kxsd9_common_remove(struct device *parent)
 {
 	struct iio_dev *indio_dev = dev_get_drvdata(parent);
 
+	iio_triggered_buffer_cleanup(indio_dev);
 	iio_device_unregister(indio_dev);
 
 	return 0;