/* 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/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/workqueue.h>
#include <linux/sched.h>
#include <linux/poll.h>
#include "ring_sw.h"
#include "trigger.h"
/**
* struct iio_sw_ring_buffer - software ring buffer
* @buf: generic ring buffer elements
* @data: the ring buffer memory
* @read_p: read pointer (oldest available)
* @write_p: write pointer
* @last_written_p: read pointer (newest available)
* @half_p: half buffer length behind write_p (event generation)
* @use_count: reference count to prevent resizing when in use
* @update_needed: flag to indicated change in size requested
* @use_lock: lock to prevent change in size when in use
*
* Note that the first element of all ring buffers must be a
* struct iio_ring_buffer.
**/
struct iio_sw_ring_buffer {
struct iio_ring_buffer buf;
unsigned char *data;
unsigned char *read_p;
unsigned char *write_p;
unsigned char *last_written_p;
/* used to act as a point at which to signal an event */
unsigned char *half_p;
int use_count;
int update_needed;
spinlock_t use_lock;
};
#define iio_to_sw_ring(r) container_of(r, struct iio_sw_ring_buffer, buf)
static inline int __iio_allocate_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_update_ring_buffer(&ring->buf, bytes_per_datum, length);
ring->data = kmalloc(length*ring->buf.bytes_per_datum, GFP_ATOMIC);
ring->read_p = NULL;
ring->write_p = NULL;
ring->last_written_p = NULL;
ring->half_p = NULL;
return ring->data ? 0 : -ENOMEM;
}
static inline void __iio_init_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
{
spin_lock_init(&ring->use_lock);
}
static inline void __iio_free_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
{
kfree(ring->data);
}
static 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);
}
static 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);
}
/* 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 */
static int iio_store_to_sw_ring(struct iio_sw_ring_buffer *ring,
unsigned char *data, s64 timestamp)
{
int ret = 0;
unsigned char *temp_ptr, *change_test_ptr;
/* initial store */
if (unlikely(ring->write_p == NULL)) {
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.bytes_per_datum/2;
}
/* Copy data to where ever the current write pointer says */
memcpy(ring->write_p, data, ring->buf.bytes_per_datum);
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.bytes_per_datum;
/* End of ring, back to the beginning */
if (temp_ptr == ring->data + ring->buf.length*ring->buf.bytes_per_datum)
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 == NULL)
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.bytes_per_datum;
if (temp_ptr
== ring->data + ring->buf.length*ring->buf.bytes_per_datum) {
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;
}
/* 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.bytes_per_datum;
if (ring->half_p == ring->data + ring->buf.length*ring->buf.bytes_per_datum)
ring->half_p = ring->data;
if (ring->half_p == ring->read_p) {
ring->buf.stufftoread = true;
wake_up_interruptible(&ring->buf.pollq);
}
return ret;
}
static int iio_read_first_n_sw_rb(struct iio_ring_buffer *r,
size_t n, char __user *buf)
{
struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
u8 *initial_read_p, *initial_write_p, *current_read_p, *end_read_p;
u8 *data;
int ret, max_copied, bytes_to_rip, dead_offset;
/* 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 (n % ring->buf.bytes_per_datum) {
ret = -EINVAL;
printk(KERN_INFO "Ring buffer read request not whole number of"
"samples: Request bytes %zd, Current bytes per datum %d\n",
n, ring->buf.bytes_per_datum);
goto error_ret;
}
/* Limit size to whole of ring buffer */
bytes_to_rip = min((size_t)(ring->buf.bytes_per_datum*ring->buf.length),
n);
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 == NULL)) { /* 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.bytes_per_datum - 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.bytes_per_datum
- (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;
ret = max_copied - dead_offset;
if (copy_to_user(buf, data + dead_offset, ret)) {
ret = -EFAULT;
goto error_free_data_cpy;
}
if (bytes_to_rip >= ring->buf.length*ring->buf.bytes_per_datum/2)
ring->buf.stufftoread = 0;
error_free_data_cpy:
kfree(data);
error_ret:
return ret;
}
static 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);
}
static 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 == NULL)
return -EAGAIN;
memcpy(data, last_written_p_copy, ring->buf.bytes_per_datum);
if (unlikely(ring->last_written_p != last_written_p_copy))
goto again;
iio_unmark_sw_rb_in_use(&ring->buf);
return 0;
}
static 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);
}
static 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);
r->stufftoread = false;
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_allocate_sw_ring_buffer(ring, ring->buf.bytes_per_datum,
ring->buf.length);
error_ret:
spin_unlock(&ring->use_lock);
return ret;
}
static int iio_get_bytes_per_datum_sw_rb(struct iio_ring_buffer *r)
{
struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
return ring->buf.bytes_per_datum;
}
static int iio_set_bytes_per_datum_sw_rb(struct iio_ring_buffer *r, size_t bpd)
{
if (r->bytes_per_datum != bpd) {
r->bytes_per_datum = bpd;
if (r->access->mark_param_change)
r->access->mark_param_change(r);
}
return 0;
}
static int iio_get_length_sw_rb(struct iio_ring_buffer *r)
{
return r->length;
}
static 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;
}
static 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;
}
static void iio_sw_rb_release(struct device *dev)
{
struct iio_ring_buffer *r = to_iio_ring_buffer(dev);
iio_ring_access_release(&r->dev);
kfree(iio_to_sw_ring(r));
}
static IIO_RING_ENABLE_ATTR;
static IIO_RING_BYTES_PER_DATUM_ATTR;
static IIO_RING_LENGTH_ATTR;
/* Standard set of ring buffer attributes */
static struct attribute *iio_ring_attributes[] = {
&dev_attr_length.attr,
&dev_attr_bytes_per_datum.attr,
&dev_attr_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 NULL;
ring->update_needed = true;
buf = &ring->buf;
iio_ring_buffer_init(buf, indio_dev);
__iio_init_sw_ring_buffer(ring);
buf->dev.type = &iio_sw_ring_type;
buf->dev.parent = &indio_dev->dev;
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);
const struct iio_ring_access_funcs ring_sw_access_funcs = {
.mark_in_use = &iio_mark_sw_rb_in_use,
.unmark_in_use = &iio_unmark_sw_rb_in_use,
.store_to = &iio_store_to_sw_rb,
.read_last = &iio_read_last_from_sw_rb,
.read_first_n = &iio_read_first_n_sw_rb,
.mark_param_change = &iio_mark_update_needed_sw_rb,
.request_update = &iio_request_update_sw_rb,
.get_bytes_per_datum = &iio_get_bytes_per_datum_sw_rb,
.set_bytes_per_datum = &iio_set_bytes_per_datum_sw_rb,
.get_length = &iio_get_length_sw_rb,
.set_length = &iio_set_length_sw_rb,
};
EXPORT_SYMBOL(ring_sw_access_funcs);
MODULE_DESCRIPTION("Industrialio I/O software ring buffer");
MODULE_LICENSE("GPL");
