368 lines
10 KiB
C
368 lines
10 KiB
C
/* The industrial I/O simple minimally locked ring buffer.
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*
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* Copyright (c) 2008 Jonathan Cameron
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*/
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#include <linux/slab.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/device.h>
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#include <linux/workqueue.h>
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#include <linux/sched.h>
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#include <linux/poll.h>
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#include "ring_sw.h"
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#include "trigger.h"
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/**
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* struct iio_sw_ring_buffer - software ring buffer
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* @buf: generic ring buffer elements
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* @data: the ring buffer memory
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* @read_p: read pointer (oldest available)
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* @write_p: write pointer
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* @half_p: half buffer length behind write_p (event generation)
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* @update_needed: flag to indicated change in size requested
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*
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* Note that the first element of all ring buffers must be a
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* struct iio_buffer.
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**/
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struct iio_sw_ring_buffer {
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struct iio_buffer buf;
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unsigned char *data;
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unsigned char *read_p;
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unsigned char *write_p;
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/* used to act as a point at which to signal an event */
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unsigned char *half_p;
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int update_needed;
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};
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#define iio_to_sw_ring(r) container_of(r, struct iio_sw_ring_buffer, buf)
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static inline int __iio_allocate_sw_ring_buffer(struct iio_sw_ring_buffer *ring,
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int bytes_per_datum, int length)
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{
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if ((length == 0) || (bytes_per_datum == 0))
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return -EINVAL;
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__iio_update_buffer(&ring->buf, bytes_per_datum, length);
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ring->data = kmalloc(length*ring->buf.bytes_per_datum, GFP_ATOMIC);
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ring->read_p = NULL;
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ring->write_p = NULL;
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ring->half_p = NULL;
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return ring->data ? 0 : -ENOMEM;
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}
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static inline void __iio_free_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
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{
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kfree(ring->data);
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}
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/* Ring buffer related functionality */
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/* Store to ring is typically called in the bh of a data ready interrupt handler
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* in the device driver */
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/* Lock always held if their is a chance this may be called */
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/* Only one of these per ring may run concurrently - enforced by drivers */
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static int iio_store_to_sw_ring(struct iio_sw_ring_buffer *ring,
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unsigned char *data, s64 timestamp)
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{
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int ret = 0;
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unsigned char *temp_ptr, *change_test_ptr;
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/* initial store */
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if (unlikely(ring->write_p == NULL)) {
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ring->write_p = ring->data;
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/* Doesn't actually matter if this is out of the set
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* as long as the read pointer is valid before this
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* passes it - guaranteed as set later in this function.
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*/
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ring->half_p = ring->data - ring->buf.length*ring->buf.bytes_per_datum/2;
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}
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/* Copy data to where ever the current write pointer says */
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memcpy(ring->write_p, data, ring->buf.bytes_per_datum);
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barrier();
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/* Update the pointer used to get most recent value.
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* Always valid as either points to latest or second latest value.
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* Before this runs it is null and read attempts fail with -EAGAIN.
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*/
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barrier();
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/* temp_ptr used to ensure we never have an invalid pointer
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* it may be slightly lagging, but never invalid
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*/
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temp_ptr = ring->write_p + ring->buf.bytes_per_datum;
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/* End of ring, back to the beginning */
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if (temp_ptr == ring->data + ring->buf.length*ring->buf.bytes_per_datum)
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temp_ptr = ring->data;
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/* Update the write pointer
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* always valid as long as this is the only function able to write.
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* Care needed with smp systems to ensure more than one ring fill
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* is never scheduled.
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*/
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ring->write_p = temp_ptr;
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if (ring->read_p == NULL)
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ring->read_p = ring->data;
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/* Buffer full - move the read pointer and create / escalate
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* ring event */
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/* Tricky case - if the read pointer moves before we adjust it.
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* Handle by not pushing if it has moved - may result in occasional
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* unnecessary buffer full events when it wasn't quite true.
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*/
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else if (ring->write_p == ring->read_p) {
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change_test_ptr = ring->read_p;
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temp_ptr = change_test_ptr + ring->buf.bytes_per_datum;
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if (temp_ptr
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== ring->data + ring->buf.length*ring->buf.bytes_per_datum) {
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temp_ptr = ring->data;
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}
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/* We are moving pointer on one because the ring is full. Any
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* change to the read pointer will be this or greater.
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*/
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if (change_test_ptr == ring->read_p)
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ring->read_p = temp_ptr;
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}
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/* investigate if our event barrier has been passed */
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/* There are definite 'issues' with this and chances of
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* simultaneous read */
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/* Also need to use loop count to ensure this only happens once */
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ring->half_p += ring->buf.bytes_per_datum;
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if (ring->half_p == ring->data + ring->buf.length*ring->buf.bytes_per_datum)
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ring->half_p = ring->data;
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if (ring->half_p == ring->read_p) {
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ring->buf.stufftoread = true;
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wake_up_interruptible(&ring->buf.pollq);
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}
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return ret;
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}
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static int iio_read_first_n_sw_rb(struct iio_buffer *r,
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size_t n, char __user *buf)
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{
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struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
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u8 *initial_read_p, *initial_write_p, *current_read_p, *end_read_p;
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u8 *data;
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int ret, max_copied, bytes_to_rip, dead_offset;
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size_t data_available, buffer_size;
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/* A userspace program has probably made an error if it tries to
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* read something that is not a whole number of bpds.
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* Return an error.
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*/
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if (n % ring->buf.bytes_per_datum) {
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ret = -EINVAL;
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printk(KERN_INFO "Ring buffer read request not whole number of"
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"samples: Request bytes %zd, Current bytes per datum %d\n",
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n, ring->buf.bytes_per_datum);
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goto error_ret;
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}
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buffer_size = ring->buf.bytes_per_datum*ring->buf.length;
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/* Limit size to whole of ring buffer */
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bytes_to_rip = min_t(size_t, buffer_size, n);
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data = kmalloc(bytes_to_rip, GFP_KERNEL);
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if (data == NULL) {
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ret = -ENOMEM;
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goto error_ret;
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}
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/* build local copy */
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initial_read_p = ring->read_p;
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if (unlikely(initial_read_p == NULL)) { /* No data here as yet */
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ret = 0;
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goto error_free_data_cpy;
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}
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initial_write_p = ring->write_p;
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/* Need a consistent pair */
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while ((initial_read_p != ring->read_p)
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|| (initial_write_p != ring->write_p)) {
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initial_read_p = ring->read_p;
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initial_write_p = ring->write_p;
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}
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if (initial_write_p == initial_read_p) {
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/* No new data available.*/
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ret = 0;
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goto error_free_data_cpy;
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}
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if (initial_write_p >= initial_read_p)
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data_available = initial_write_p - initial_read_p;
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else
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data_available = buffer_size - (initial_read_p - initial_write_p);
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if (data_available < bytes_to_rip)
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bytes_to_rip = data_available;
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if (initial_read_p + bytes_to_rip >= ring->data + buffer_size) {
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max_copied = ring->data + buffer_size - initial_read_p;
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memcpy(data, initial_read_p, max_copied);
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memcpy(data + max_copied, ring->data, bytes_to_rip - max_copied);
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end_read_p = ring->data + bytes_to_rip - max_copied;
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} else {
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memcpy(data, initial_read_p, bytes_to_rip);
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end_read_p = initial_read_p + bytes_to_rip;
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}
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/* Now to verify which section was cleanly copied - i.e. how far
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* read pointer has been pushed */
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current_read_p = ring->read_p;
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if (initial_read_p <= current_read_p)
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dead_offset = current_read_p - initial_read_p;
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else
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dead_offset = buffer_size - (initial_read_p - current_read_p);
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/* possible issue if the initial write has been lapped or indeed
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* the point we were reading to has been passed */
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/* No valid data read.
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* In this case the read pointer is already correct having been
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* pushed further than we would look. */
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if (bytes_to_rip - dead_offset < 0) {
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ret = 0;
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goto error_free_data_cpy;
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}
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/* setup the next read position */
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/* Beware, this may fail due to concurrency fun and games.
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* Possible that sufficient fill commands have run to push the read
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* pointer past where we would be after the rip. If this occurs, leave
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* it be.
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*/
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/* Tricky - deal with loops */
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while (ring->read_p != end_read_p)
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ring->read_p = end_read_p;
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ret = bytes_to_rip - dead_offset;
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if (copy_to_user(buf, data + dead_offset, ret)) {
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ret = -EFAULT;
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goto error_free_data_cpy;
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}
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if (bytes_to_rip >= ring->buf.length*ring->buf.bytes_per_datum/2)
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ring->buf.stufftoread = 0;
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error_free_data_cpy:
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kfree(data);
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error_ret:
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return ret;
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}
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static int iio_store_to_sw_rb(struct iio_buffer *r,
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u8 *data,
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s64 timestamp)
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{
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struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
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return iio_store_to_sw_ring(ring, data, timestamp);
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}
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static int iio_request_update_sw_rb(struct iio_buffer *r)
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{
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int ret = 0;
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struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
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r->stufftoread = false;
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if (!ring->update_needed)
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goto error_ret;
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__iio_free_sw_ring_buffer(ring);
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ret = __iio_allocate_sw_ring_buffer(ring, ring->buf.bytes_per_datum,
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ring->buf.length);
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error_ret:
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return ret;
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}
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static int iio_get_bytes_per_datum_sw_rb(struct iio_buffer *r)
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{
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struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
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return ring->buf.bytes_per_datum;
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}
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static int iio_mark_update_needed_sw_rb(struct iio_buffer *r)
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{
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struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
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ring->update_needed = true;
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return 0;
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}
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static int iio_set_bytes_per_datum_sw_rb(struct iio_buffer *r, size_t bpd)
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{
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if (r->bytes_per_datum != bpd) {
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r->bytes_per_datum = bpd;
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iio_mark_update_needed_sw_rb(r);
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}
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return 0;
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}
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static int iio_get_length_sw_rb(struct iio_buffer *r)
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{
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return r->length;
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}
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static int iio_set_length_sw_rb(struct iio_buffer *r, int length)
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{
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if (r->length != length) {
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r->length = length;
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iio_mark_update_needed_sw_rb(r);
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}
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return 0;
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}
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static IIO_BUFFER_ENABLE_ATTR;
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static IIO_BUFFER_LENGTH_ATTR;
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/* Standard set of ring buffer attributes */
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static struct attribute *iio_ring_attributes[] = {
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&dev_attr_length.attr,
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&dev_attr_enable.attr,
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NULL,
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};
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static struct attribute_group iio_ring_attribute_group = {
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.attrs = iio_ring_attributes,
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.name = "buffer",
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};
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static const struct iio_buffer_access_funcs ring_sw_access_funcs = {
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.store_to = &iio_store_to_sw_rb,
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.read_first_n = &iio_read_first_n_sw_rb,
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.request_update = &iio_request_update_sw_rb,
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.get_bytes_per_datum = &iio_get_bytes_per_datum_sw_rb,
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.set_bytes_per_datum = &iio_set_bytes_per_datum_sw_rb,
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.get_length = &iio_get_length_sw_rb,
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.set_length = &iio_set_length_sw_rb,
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};
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struct iio_buffer *iio_sw_rb_allocate(struct iio_dev *indio_dev)
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{
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struct iio_buffer *buf;
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struct iio_sw_ring_buffer *ring;
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ring = kzalloc(sizeof *ring, GFP_KERNEL);
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if (!ring)
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return NULL;
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ring->update_needed = true;
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buf = &ring->buf;
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iio_buffer_init(buf);
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buf->attrs = &iio_ring_attribute_group;
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buf->access = &ring_sw_access_funcs;
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return buf;
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}
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EXPORT_SYMBOL(iio_sw_rb_allocate);
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void iio_sw_rb_free(struct iio_buffer *r)
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{
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kfree(iio_to_sw_ring(r));
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}
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EXPORT_SYMBOL(iio_sw_rb_free);
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MODULE_DESCRIPTION("Industrialio I/O software ring buffer");
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MODULE_LICENSE("GPL");
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