Staging: IIO: VTI sca3000 series accelerometer driver (spi)

Example of how a device with a hardware ring buffer is
handled within IIO.

Changes since V2:
* Moved to new registration functions giving much cleaner
  interface.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 331 insertions, 0 deletions

diff --git a/drivers/staging/iio/accel/sca3000_ring.c b/drivers/staging/iio/accel/sca3000_ring.c
new file mode 100644
index 000000000000..b01876d1dbc6
--- /dev/null
+++ b/drivers/staging/iio/accel/sca3000_ring.c
@@ -0,0 +1,331 @@
+/*
+ * sca3000_ring.c -- support VTI sca3000 series accelerometers via SPI
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * Copyright (c) 2009 Jonathan Cameron <jic23@cam.ac.uk>
+ *
+ */
+
+#include <linux/interrupt.h>
+#include <linux/gpio.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/spi/spi.h>
+#include <linux/sysfs.h>
+
+#include "../iio.h"
+#include "../sysfs.h"
+#include "../ring_generic.h"
+#include "../ring_hw.h"
+#include "accel.h"
+#include "sca3000.h"
+
+/* RFC / future work
+ *
+ * The internal ring buffer doesn't actually change what it holds depending
+ * on which signals are enabled etc, merely whether you can read them.
+ * As such the scan mode selection is somewhat different than for a software
+ * ring buffer and changing it actually covers any data already in the buffer.
+ * Currently scan elements aren't configured so it doesn't matter.
+ */
+
+/**
+ * sca3000_rip_hw_rb() - main ring access function, pulls data from ring
+ * @r:			the ring
+ * @count:		number of samples to try and pull
+ * @data:		output the actual samples pulled from the hw ring
+ * @dead_offset:	cheating a bit here: Set to 1 so as to allow for the
+ *			leading byte used in bus comms.
+ *
+ * Currently does not provide timestamps.  As the hardware doesn't add them they
+ * can only be inferred aproximately from ring buffer events such as 50% full
+ * and knowledge of when buffer was last emptied.  This is left to userspace.
+ **/
+static int sca3000_rip_hw_rb(struct iio_ring_buffer *r,
+			     size_t count, u8 **data, int *dead_offset)
+{
+	struct iio_hw_ring_buffer *hw_ring = iio_to_hw_ring_buf(r);
+	struct iio_dev *indio_dev = hw_ring->private;
+	struct sca3000_state *st = indio_dev->dev_data;
+	u8 *rx;
+	int ret, num_available, num_read = 0;
+	int bytes_per_sample = 1;
+
+	if (st->bpse == 11)
+		bytes_per_sample = 2;
+
+	mutex_lock(&st->lock);
+	/* Check how much data is available:
+	 * RFC: Implement an ioctl to not bother checking whether there
+	 * is enough data in the ring?  Afterall, if we are responding
+	 * to an interrupt we have a minimum content guaranteed so it
+	 * seems slight silly to waste time checking it is there.
+	 */
+	ret = sca3000_read_data(st,
+				SCA3000_REG_ADDR_BUF_COUNT,
+				&rx, 1);
+	if (ret)
+		goto error_ret;
+	else
+		num_available = rx[1];
+	/* num_available is the total number of samples available
+	 * i.e. number of time points * number of channels.
+	 */
+	kfree(rx);
+	if (count > num_available * bytes_per_sample)
+		num_read = num_available*bytes_per_sample;
+	else
+		num_read = count - (count % (bytes_per_sample));
+
+	/* Avoid the read request byte */
+	*dead_offset = 1;
+	ret = sca3000_read_data(st,
+				SCA3000_REG_ADDR_RING_OUT,
+				data, num_read);
+error_ret:
+	mutex_unlock(&st->lock);
+
+	return ret ? ret : num_read;
+}
+
+/* This is only valid with all 3 elements enabled */
+static int sca3000_ring_get_length(struct iio_ring_buffer *r)
+{
+	return 64;
+}
+
+/* only valid if resolution is kept at 11bits */
+static int sca3000_ring_get_bpd(struct iio_ring_buffer *r)
+{
+	return 6;
+}
+static void sca3000_ring_release(struct device *dev)
+{
+	struct iio_ring_buffer *r = to_iio_ring_buffer(dev);
+	kfree(iio_to_hw_ring_buf(r));
+}
+
+static IIO_RING_ENABLE_ATTR;
+static IIO_RING_BPS_ATTR;
+static IIO_RING_LENGTH_ATTR;
+
+/**
+ * sca3000_show_ring_bpse() -sysfs function to query bits per sample from ring
+ * @dev: ring buffer device
+ * @attr: this device attribute
+ * @buf: buffer to write to
+ **/
+static ssize_t sca3000_show_ring_bpse(struct device *dev,
+				      struct device_attribute *attr,
+				      char *buf)
+{
+	int len = 0, ret;
+	u8 *rx;
+	struct iio_ring_buffer *r = dev_get_drvdata(dev);
+	struct sca3000_state *st = r->indio_dev->dev_data;
+
+	mutex_lock(&st->lock);
+	ret = sca3000_read_data(st, SCA3000_REG_ADDR_MODE, &rx, 1);
+	if (ret)
+		goto error_ret;
+	len = sprintf(buf, "%d\n", (rx[1] & SCA3000_RING_BUF_8BIT) ? 8 : 11);
+	kfree(rx);
+error_ret:
+	mutex_unlock(&st->lock);
+
+	return ret ? ret : len;
+}
+
+/**
+ * sca3000_store_ring_bpse() - bits per scan element
+ * @dev: ring buffer device
+ * @attr: attribute called from
+ * @buf: input from userspace
+ * @len: length of input
+ **/
+static ssize_t sca3000_store_ring_bpse(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t len)
+{
+	struct iio_ring_buffer *r = dev_get_drvdata(dev);
+	struct sca3000_state *st = r->indio_dev->dev_data;
+	int ret;
+	u8 *rx;
+	long val;
+	ret = strict_strtol(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	mutex_lock(&st->lock);
+
+	ret = sca3000_read_data(st, SCA3000_REG_ADDR_MODE, &rx, 1);
+	if (!ret)
+		switch (val) {
+		case 8:
+			ret = sca3000_write_reg(st, SCA3000_REG_ADDR_MODE,
+						rx[1] | SCA3000_RING_BUF_8BIT);
+			st->bpse = 8;
+			break;
+		case 11:
+			ret = sca3000_write_reg(st, SCA3000_REG_ADDR_MODE,
+						rx[1] & ~SCA3000_RING_BUF_8BIT);
+			st->bpse = 11;
+			break;
+		default:
+			ret = -EINVAL;
+			break;
+		}
+	mutex_unlock(&st->lock);
+
+	return ret ? ret : len;
+}
+
+static IIO_CONST_ATTR(bpse_available, "8 11");
+
+static IIO_DEV_ATTR_BPSE(S_IRUGO | S_IWUSR,
+			      sca3000_show_ring_bpse,
+			      sca3000_store_ring_bpse);
+
+/*
+ * Ring buffer attributes
+ * This device is a bit unusual in that the sampling frequency and bpse
+ * only apply to the ring buffer.  At all times full rate and accuracy
+ * is available via direct reading from registers.
+ */
+static struct attribute *iio_ring_attributes[] = {
+	&dev_attr_length.attr,
+	&dev_attr_bps.attr,
+	&dev_attr_ring_enable.attr,
+	&iio_dev_attr_bpse.dev_attr.attr,
+	&iio_const_attr_bpse_available.dev_attr.attr,
+	NULL,
+};
+
+static struct attribute_group sca3000_ring_attr = {
+	.attrs = iio_ring_attributes,
+};
+
+static struct attribute_group *sca3000_ring_attr_groups[] = {
+	&sca3000_ring_attr,
+	NULL
+};
+
+static struct device_type sca3000_ring_type = {
+	.release = sca3000_ring_release,
+	.groups = sca3000_ring_attr_groups,
+};
+
+static struct iio_ring_buffer *sca3000_rb_allocate(struct iio_dev *indio_dev)
+{
+	struct iio_ring_buffer *buf;
+	struct iio_hw_ring_buffer *ring;
+
+	ring = kzalloc(sizeof *ring, GFP_KERNEL);
+	if (!ring)
+		return 0;
+	ring->private = indio_dev;
+	buf = &ring->buf;
+	iio_ring_buffer_init(buf, indio_dev);
+	buf->dev.type = &sca3000_ring_type;
+	device_initialize(&buf->dev);
+	buf->dev.parent = &indio_dev->dev;
+	dev_set_drvdata(&buf->dev, (void *)buf);
+
+	return buf;
+}
+
+static inline void sca3000_rb_free(struct iio_ring_buffer *r)
+{
+	if (r)
+		iio_put_ring_buffer(r);
+}
+
+int sca3000_configure_ring(struct iio_dev *indio_dev)
+{
+	indio_dev->ring = sca3000_rb_allocate(indio_dev);
+	if (indio_dev->ring == NULL)
+		return -ENOMEM;
+	indio_dev->modes |= INDIO_RING_HARDWARE_BUFFER;
+
+	indio_dev->ring->access.rip_lots = &sca3000_rip_hw_rb;
+	indio_dev->ring->access.get_length = &sca3000_ring_get_length;
+	indio_dev->ring->access.get_bpd = &sca3000_ring_get_bpd;
+
+	return 0;
+}
+
+void sca3000_unconfigure_ring(struct iio_dev *indio_dev)
+{
+	sca3000_rb_free(indio_dev->ring);
+}
+
+static inline
+int __sca3000_hw_ring_state_set(struct iio_dev *indio_dev, bool state)
+{
+	struct sca3000_state *st = indio_dev->dev_data;
+	int ret;
+	u8 *rx;
+
+	mutex_lock(&st->lock);
+	ret = sca3000_read_data(st, SCA3000_REG_ADDR_MODE, &rx, 1);
+	if (ret)
+		goto error_ret;
+	if (state) {
+		printk(KERN_INFO "supposedly enabling ring buffer\n");
+		ret = sca3000_write_reg(st,
+					SCA3000_REG_ADDR_MODE,
+					(rx[1] | SCA3000_RING_BUF_ENABLE));
+	} else
+		ret = sca3000_write_reg(st,
+					SCA3000_REG_ADDR_MODE,
+					(rx[1] & ~SCA3000_RING_BUF_ENABLE));
+	kfree(rx);
+error_ret:
+	mutex_unlock(&st->lock);
+
+	return ret;
+}
+/**
+ * sca3000_hw_ring_preenable() hw ring buffer preenable function
+ *
+ * Very simple enable function as the chip will allows normal reads
+ * during ring buffer operation so as long as it is indeed running
+ * before we notify the core, the precise ordering does not matter.
+ **/
+static int sca3000_hw_ring_preenable(struct iio_dev *indio_dev)
+{
+	return __sca3000_hw_ring_state_set(indio_dev, 1);
+}
+
+static int sca3000_hw_ring_postdisable(struct iio_dev *indio_dev)
+{
+	return __sca3000_hw_ring_state_set(indio_dev, 0);
+}
+
+void sca3000_register_ring_funcs(struct iio_dev *indio_dev)
+{
+	indio_dev->ring->preenable = &sca3000_hw_ring_preenable;
+	indio_dev->ring->postdisable = &sca3000_hw_ring_postdisable;
+}
+
+/**
+ * sca3000_ring_int_process() ring specific interrupt handling.
+ *
+ * This is only split from the main interrupt handler so as to
+ * reduce the amount of code if the ring buffer is not enabled.
+ **/
+void sca3000_ring_int_process(u8 val, struct iio_ring_buffer *ring)
+{
+	if (val & SCA3000_INT_STATUS_THREE_QUARTERS)
+		iio_push_or_escallate_ring_event(ring,
+						 IIO_EVENT_CODE_RING_75_FULL,
+						 0);
+	else if (val & SCA3000_INT_STATUS_HALF)
+		iio_push_ring_event(ring,
+				    IIO_EVENT_CODE_RING_50_FULL, 0);
+}