text: /* The industrial I/O simple minimally locked ring buffer.
   *
   * Copyright (c) 2008 Jonathan Cameron
   *
   * 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.
   */
  
  #include <linux/kernel.h>
  #include <linux/device.h>
  #include <linux/module.h>
  #include <linux/device.h>
  #include <linux/workqueue.h>
  #include "ring_sw.h"
  
  static inline int __iio_init_sw_ring_buffer(struct iio_sw_ring_buffer *ring,
  					    int bytes_per_datum, int length)
  {
  	if ((length == 0) || (bytes_per_datum == 0))
  		return -EINVAL;
  
  	__iio_init_ring_buffer(&ring->buf, bytes_per_datum, length);
  	ring->use_lock = __SPIN_LOCK_UNLOCKED((ring)->use_lock);
  	ring->data = kmalloc(length*ring->buf.bpd, GFP_KERNEL);
  	ring->read_p = 0;
  	ring->write_p = 0;
  	ring->last_written_p = 0;
  	ring->half_p = 0;
  	return ring->data ? 0 : -ENOMEM;
  }
  
  static inline void __iio_free_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
  {
  	kfree(ring->data);
  }
  
  void iio_mark_sw_rb_in_use(struct iio_ring_buffer *r)
  {
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  	spin_lock(&ring->use_lock);
  	ring->use_count++;
  	spin_unlock(&ring->use_lock);
  }
  EXPORT_SYMBOL(iio_mark_sw_rb_in_use);
  
  void iio_unmark_sw_rb_in_use(struct iio_ring_buffer *r)
  {
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  	spin_lock(&ring->use_lock);
  	ring->use_count--;
  	spin_unlock(&ring->use_lock);
  }
  EXPORT_SYMBOL(iio_unmark_sw_rb_in_use);
  
  
  /* Ring buffer related functionality */
  /* Store to ring is typically called in the bh of a data ready interrupt handler
   * in the device driver */
  /* Lock always held if their is a chance this may be called */
  /* Only one of these per ring may run concurrently - enforced by drivers */
  int iio_store_to_sw_ring(struct iio_sw_ring_buffer *ring,
  			 unsigned char *data,
  			 s64 timestamp)
  {
  	int ret = 0;
  	int code;
  	unsigned char *temp_ptr, *change_test_ptr;
  
  	/* initial store */
  	if (unlikely(ring->write_p == 0)) {
  		ring->write_p = ring->data;
  		/* Doesn't actually matter if this is out of the set
  		 * as long as the read pointer is valid before this
  		 * passes it - guaranteed as set later in this function.
  		 */
  		ring->half_p = ring->data - ring->buf.length*ring->buf.bpd/2;
  	}
  	/* Copy data to where ever the current write pointer says */
  	memcpy(ring->write_p, data, ring->buf.bpd);
  	barrier();
  	/* Update the pointer used to get most recent value.
  	 * Always valid as either points to latest or second latest value.
  	 * Before this runs it is null and read attempts fail with -EAGAIN.
  	 */
  	ring->last_written_p = ring->write_p;
  	barrier();
  	/* temp_ptr used to ensure we never have an invalid pointer
  	 * it may be slightly lagging, but never invalid
  	 */
  	temp_ptr = ring->write_p + ring->buf.bpd;
  	/* End of ring, back to the beginning */
  	if (temp_ptr == ring->data + ring->buf.length*ring->buf.bpd)
  		temp_ptr = ring->data;
  	/* Update the write pointer
  	 * always valid as long as this is the only function able to write.
  	 * Care needed with smp systems to ensure more than one ring fill
  	 * is never scheduled.
  	 */
  	ring->write_p = temp_ptr;
  
  	if (ring->read_p == 0)
  		ring->read_p = ring->data;
  	/* Buffer full - move the read pointer and create / escalate
  	 * ring event */
  	/* Tricky case - if the read pointer moves before we adjust it.
  	 * Handle by not pushing if it has moved - may result in occasional
  	 * unnecessary buffer full events when it wasn't quite true.
  	 */
  	else if (ring->write_p == ring->read_p) {
  		change_test_ptr = ring->read_p;
  		temp_ptr = change_test_ptr + ring->buf.bpd;
  		if (temp_ptr
  		    == ring->data + ring->buf.length*ring->buf.bpd) {
  			temp_ptr = ring->data;
  		}
  		/* We are moving pointer on one because the ring is full.  Any
  		 * change to the read pointer will be this or greater.
  		 */
  		if (change_test_ptr == ring->read_p)
  			ring->read_p = temp_ptr;
  
  		spin_lock(&ring->buf.shared_ev_pointer.lock);
  
  		ret = iio_push_or_escallate_ring_event(&ring->buf,
  						       IIO_EVENT_CODE_RING_100_FULL,
  						       timestamp);
  		spin_unlock(&ring->buf.shared_ev_pointer.lock);
  		if (ret)
  			goto error_ret;
  	}
  	/* investigate if our event barrier has been passed */
  	/* There are definite 'issues' with this and chances of
  	 * simultaneous read */
  	/* Also need to use loop count to ensure this only happens once */
  	ring->half_p += ring->buf.bpd;
  	if (ring->half_p == ring->data + ring->buf.length*ring->buf.bpd)
  		ring->half_p = ring->data;
  	if (ring->half_p == ring->read_p) {
  		spin_lock(&ring->buf.shared_ev_pointer.lock);
  		code = IIO_EVENT_CODE_RING_50_FULL;
  		ret = __iio_push_event(&ring->buf.ev_int,
  				       code,
  				       timestamp,
  				       &ring->buf.shared_ev_pointer);
  		spin_unlock(&ring->buf.shared_ev_pointer.lock);
  	}
  error_ret:
  	return ret;
  }
  
  int iio_rip_sw_rb(struct iio_ring_buffer *r,
  		  size_t count, u8 **data, int *dead_offset)
  {
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  
  	u8 *initial_read_p, *initial_write_p, *current_read_p, *end_read_p;
  	int ret, max_copied;
  	int bytes_to_rip;
  
  	/* A userspace program has probably made an error if it tries to
  	 *  read something that is not a whole number of bpds.
  	 * Return an error.
  	 */
  	if (count % ring->buf.bpd) {
  		ret = -EINVAL;
  		printk(KERN_INFO "Ring buffer read request not whole number of"
  		       "samples: Request bytes %zd, Current bpd %d\n",
  		       count, ring->buf.bpd);
  		goto error_ret;
  	}
  	/* Limit size to whole of ring buffer */
  	bytes_to_rip = min((size_t)(ring->buf.bpd*ring->buf.length), count);
  
  	*data = kmalloc(bytes_to_rip, GFP_KERNEL);
  	if (*data == NULL) {
  		ret = -ENOMEM;
  		goto error_ret;
  	}
  
  	/* build local copy */
  	initial_read_p = ring->read_p;
  	if (unlikely(initial_read_p == 0)) { /* No data here as yet */
  		ret = 0;
  		goto error_free_data_cpy;
  	}
  
  	initial_write_p = ring->write_p;
  
  	/* Need a consistent pair */
  	while ((initial_read_p != ring->read_p)
  	       || (initial_write_p != ring->write_p)) {
  		initial_read_p = ring->read_p;
  		initial_write_p = ring->write_p;
  	}
  	if (initial_write_p == initial_read_p) {
  		/* No new data available.*/
  		ret = 0;
  		goto error_free_data_cpy;
  	}
  
  	if (initial_write_p >= initial_read_p + bytes_to_rip) {
  		/* write_p is greater than necessary, all is easy */
  		max_copied = bytes_to_rip;
  		memcpy(*data, initial_read_p, max_copied);
  		end_read_p = initial_read_p + max_copied;
  	} else if (initial_write_p > initial_read_p) {
  		/*not enough data to cpy */
  		max_copied = initial_write_p - initial_read_p;
  		memcpy(*data, initial_read_p, max_copied);
  		end_read_p = initial_write_p;
  	} else {
  		/* going through 'end' of ring buffer */
  		max_copied = ring->data
  			+ ring->buf.length*ring->buf.bpd - initial_read_p;
  		memcpy(*data, initial_read_p, max_copied);
  		/* possible we are done if we align precisely with end */
  		if (max_copied == bytes_to_rip)
  			end_read_p = ring->data;
  		else if (initial_write_p
  			 > ring->data + bytes_to_rip - max_copied) {
  			/* enough data to finish */
  			memcpy(*data + max_copied, ring->data,
  			       bytes_to_rip - max_copied);
  			max_copied = bytes_to_rip;
  			end_read_p = ring->data + (bytes_to_rip - max_copied);
  		} else {  /* not enough data */
  			memcpy(*data + max_copied, ring->data,
  			       initial_write_p - ring->data);
  			max_copied += initial_write_p - ring->data;
  			end_read_p = initial_write_p;
  		}
  	}
  	/* Now to verify which section was cleanly copied - i.e. how far
  	 * read pointer has been pushed */
  	current_read_p = ring->read_p;
  
  	if (initial_read_p <= current_read_p)
  		*dead_offset = current_read_p - initial_read_p;
  	else
  		*dead_offset = ring->buf.length*ring->buf.bpd
  			- (initial_read_p - current_read_p);
  
  	/* possible issue if the initial write has been lapped or indeed
  	 * the point we were reading to has been passed */
  	/* No valid data read.
  	 * In this case the read pointer is already correct having been
  	 * pushed further than we would look. */
  	if (max_copied - *dead_offset < 0) {
  		ret = 0;
  		goto error_free_data_cpy;
  	}
  
  	/* setup the next read position */
  	/* Beware, this may fail due to concurrency fun and games.
  	 *  Possible that sufficient fill commands have run to push the read
  	 * pointer past where we would be after the rip. If this occurs, leave
  	 * it be.
  	 */
  	/* Tricky - deal with loops */
  
  	while (ring->read_p != end_read_p)
  		ring->read_p = end_read_p;
  
  	return max_copied - *dead_offset;
  
  error_free_data_cpy:
  	kfree(*data);
  error_ret:
  	return ret;
  }
  EXPORT_SYMBOL(iio_rip_sw_rb);
  
  int iio_store_to_sw_rb(struct iio_ring_buffer *r, u8 *data, s64 timestamp)
  {
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  	return iio_store_to_sw_ring(ring, data, timestamp);
  }
  EXPORT_SYMBOL(iio_store_to_sw_rb);
  
  int iio_read_last_from_sw_ring(struct iio_sw_ring_buffer *ring,
  			       unsigned char *data)
  {
  	unsigned char *last_written_p_copy;
  
  	iio_mark_sw_rb_in_use(&ring->buf);
  again:
  	barrier();
  	last_written_p_copy = ring->last_written_p;
  	barrier(); /*unnessecary? */
  	/* Check there is anything here */
  	if (last_written_p_copy == 0)
  		return -EAGAIN;
  	memcpy(data, last_written_p_copy, ring->buf.bpd);
  
  	if (unlikely(ring->last_written_p >= last_written_p_copy))
  		goto again;
  
  	iio_unmark_sw_rb_in_use(&ring->buf);
  	return 0;
  }
  
  int iio_read_last_from_sw_rb(struct iio_ring_buffer *r,
  			     unsigned char *data)
  {
  	return iio_read_last_from_sw_ring(iio_to_sw_ring(r), data);
  }
  EXPORT_SYMBOL(iio_read_last_from_sw_rb);
  
  int iio_request_update_sw_rb(struct iio_ring_buffer *r)
  {
  	int ret = 0;
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  
  	spin_lock(&ring->use_lock);
  	if (!ring->update_needed)
  		goto error_ret;
  	if (ring->use_count) {
  		ret = -EAGAIN;
  		goto error_ret;
  	}
  	__iio_free_sw_ring_buffer(ring);
  	ret = __iio_init_sw_ring_buffer(ring, ring->buf.bpd, ring->buf.length);
  error_ret:
  	spin_unlock(&ring->use_lock);
  	return ret;
  }
  EXPORT_SYMBOL(iio_request_update_sw_rb);
  
  int iio_get_bpd_sw_rb(struct iio_ring_buffer *r)
  {
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  	return ring->buf.bpd;
  }
  EXPORT_SYMBOL(iio_get_bpd_sw_rb);
  
  int iio_set_bpd_sw_rb(struct iio_ring_buffer *r, size_t bpd)
  {
  	if (r->bpd != bpd) {
  		r->bpd = bpd;
  		if (r->access.mark_param_change)
  			r->access.mark_param_change(r);
  	}
  	return 0;
  }
  EXPORT_SYMBOL(iio_set_bpd_sw_rb);
  
  int iio_get_length_sw_rb(struct iio_ring_buffer *r)
  {
  	return r->length;
  }
  EXPORT_SYMBOL(iio_get_length_sw_rb);
  
  int iio_set_length_sw_rb(struct iio_ring_buffer *r, int length)
  {
  	if (r->length != length) {
  		r->length = length;
  		if (r->access.mark_param_change)
  			r->access.mark_param_change(r);
  	}
  	return 0;
  }
  EXPORT_SYMBOL(iio_set_length_sw_rb);
  
  int iio_mark_update_needed_sw_rb(struct iio_ring_buffer *r)
  {
  	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  	ring->update_needed = true;
  	return 0;
  }
  EXPORT_SYMBOL(iio_mark_update_needed_sw_rb);
  
  static void iio_sw_rb_release(struct device *dev)
  {
  	struct iio_ring_buffer *r = to_iio_ring_buffer(dev);
  	kfree(iio_to_sw_ring(r));
  }
  
  static IIO_RING_ENABLE_ATTR;
  static IIO_RING_BPS_ATTR;
  static IIO_RING_LENGTH_ATTR;
  
  /* Standard set of ring buffer attributes */
  static struct attribute *iio_ring_attributes[] = {
  	&dev_attr_length.attr,
  	&dev_attr_bps.attr,
  	&dev_attr_ring_enable.attr,
  	NULL,
  };
  
  static struct attribute_group iio_ring_attribute_group = {
  	.attrs = iio_ring_attributes,
  };
  
  static const struct attribute_group *iio_ring_attribute_groups[] = {
  	&iio_ring_attribute_group,
  	NULL
  };
  
  static struct device_type iio_sw_ring_type = {
  	.release = iio_sw_rb_release,
  	.groups = iio_ring_attribute_groups,
  };
  
  struct iio_ring_buffer *iio_sw_rb_allocate(struct iio_dev *indio_dev)
  {
  	struct iio_ring_buffer *buf;
  	struct iio_sw_ring_buffer *ring;
  
  	ring = kzalloc(sizeof *ring, GFP_KERNEL);
  	if (!ring)
  		return 0;
  	buf = &ring->buf;
  
  	iio_ring_buffer_init(buf, indio_dev);
  	buf->dev.type = &iio_sw_ring_type;
  	device_initialize(&buf->dev);
  	buf->dev.parent = &indio_dev->dev;
  	buf->dev.class = &iio_class;
  	dev_set_drvdata(&buf->dev, (void *)buf);
  
  	return buf;
  }
  EXPORT_SYMBOL(iio_sw_rb_allocate);
  
  void iio_sw_rb_free(struct iio_ring_buffer *r)
  {
  	if (r)
  		iio_put_ring_buffer(r);
  }
  EXPORT_SYMBOL(iio_sw_rb_free);
  MODULE_DESCRIPTION("Industrialio I/O software ring buffer");
  MODULE_LICENSE("GPL");
  