swh:1:snp:173f8deb0c56c557784b4fd217e7608ac6197844
Tip revision: d65b4e98d7ea3038b767b70fe8be959b2913f16d authored by Linus Torvalds on 09 February 2012, 03:21:53 UTC
Linux 3.3-rc3
Linux 3.3-rc3
Tip revision: d65b4e9
ring_sw.c
/* 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
* @half_p: half buffer length behind write_p (event generation)
* @update_needed: flag to indicated change in size requested
*
* Note that the first element of all ring buffers must be a
* struct iio_buffer.
**/
struct iio_sw_ring_buffer {
struct iio_buffer buf;
unsigned char *data;
unsigned char *read_p;
unsigned char *write_p;
/* used to act as a point at which to signal an event */
unsigned char *half_p;
int update_needed;
};
#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_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->half_p = NULL;
return ring->data ? 0 : -ENOMEM;
}
static inline void __iio_free_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
{
kfree(ring->data);
}
/* 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.
*/
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_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;
size_t data_available, buffer_size;
/* 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;
}
buffer_size = ring->buf.bytes_per_datum*ring->buf.length;
/* Limit size to whole of ring buffer */
bytes_to_rip = min_t(size_t, buffer_size, 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)
data_available = initial_write_p - initial_read_p;
else
data_available = buffer_size - (initial_read_p - initial_write_p);
if (data_available < bytes_to_rip)
bytes_to_rip = data_available;
if (initial_read_p + bytes_to_rip >= ring->data + buffer_size) {
max_copied = ring->data + buffer_size - initial_read_p;
memcpy(data, initial_read_p, max_copied);
memcpy(data + max_copied, ring->data, bytes_to_rip - max_copied);
end_read_p = ring->data + bytes_to_rip - max_copied;
} else {
memcpy(data, initial_read_p, bytes_to_rip);
end_read_p = initial_read_p + bytes_to_rip;
}
/* 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 = buffer_size - (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 (bytes_to_rip - 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 = bytes_to_rip - 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_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_request_update_sw_rb(struct iio_buffer *r)
{
int ret = 0;
struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
r->stufftoread = false;
if (!ring->update_needed)
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:
return ret;
}
static int iio_get_bytes_per_datum_sw_rb(struct iio_buffer *r)
{
struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
return ring->buf.bytes_per_datum;
}
static int iio_mark_update_needed_sw_rb(struct iio_buffer *r)
{
struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
ring->update_needed = true;
return 0;
}
static int iio_set_bytes_per_datum_sw_rb(struct iio_buffer *r, size_t bpd)
{
if (r->bytes_per_datum != bpd) {
r->bytes_per_datum = bpd;
iio_mark_update_needed_sw_rb(r);
}
return 0;
}
static int iio_get_length_sw_rb(struct iio_buffer *r)
{
return r->length;
}
static int iio_set_length_sw_rb(struct iio_buffer *r, int length)
{
if (r->length != length) {
r->length = length;
iio_mark_update_needed_sw_rb(r);
}
return 0;
}
static IIO_BUFFER_ENABLE_ATTR;
static IIO_BUFFER_LENGTH_ATTR;
/* Standard set of ring buffer attributes */
static struct attribute *iio_ring_attributes[] = {
&dev_attr_length.attr,
&dev_attr_enable.attr,
NULL,
};
static struct attribute_group iio_ring_attribute_group = {
.attrs = iio_ring_attributes,
.name = "buffer",
};
struct iio_buffer *iio_sw_rb_allocate(struct iio_dev *indio_dev)
{
struct iio_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_buffer_init(buf);
buf->attrs = &iio_ring_attribute_group;
return buf;
}
EXPORT_SYMBOL(iio_sw_rb_allocate);
void iio_sw_rb_free(struct iio_buffer *r)
{
kfree(iio_to_sw_ring(r));
}
EXPORT_SYMBOL(iio_sw_rb_free);
const struct iio_buffer_access_funcs ring_sw_access_funcs = {
.store_to = &iio_store_to_sw_rb,
.read_first_n = &iio_read_first_n_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");