staging:iio: drop sw_ring buffer implementation.

Whilst this is IIO's oldest buffer implementation it is messy, poorly
implemented and whilst it works, no one is entirely sure it always will.

New IIO drivers have not been using this for some time and now all remaining
old users have been converted to use the kfifo based alternative.

Clearly a fifo isn't the same as a ring buffer but in many use cases it
really doesn't matter.  We also loose the watershed based poll implementation.
However having poll effectively report data only when the buffer was half
full was at best an 'unusual' use of the interface.

At somepoint in the future we may bring watersheds back on a different
buffer implementation, but then we will think a lot more about how to do
the interface first.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/Kconfig

@@ -12,19 +12,6 @@ config IIO_ST_HWMON
 	  map allows IIO devices to provide  basic hwmon functionality
 	  for those channels specified in the map.
 
-if IIO_BUFFER
-
-config IIO_SW_RING
-       select IIO_TRIGGER
-	tristate "Industrial I/O lock free software ring"
-	help
-	  Example software ring buffer implementation.  The design aim
-	  of this particular realization was to minimize write locking
-	  with the intention that some devices would be able to write
-	  in interrupt context.
-
-endif # IIO_BUFFER
-
 source "drivers/staging/iio/accel/Kconfig"
 source "drivers/staging/iio/adc/Kconfig"
 source "drivers/staging/iio/addac/Kconfig"

drivers/staging/iio/Makefile

@@ -2,8 +2,6 @@
 # Makefile for the industrial I/O core.
 #
 
-obj-$(CONFIG_IIO_SW_RING) += ring_sw.o
-
 obj-$(CONFIG_IIO_SIMPLE_DUMMY) += iio_dummy.o
 iio_dummy-y := iio_simple_dummy.o
 iio_dummy-$(CONFIG_IIO_SIMPLE_DUMMY_EVENTS) += iio_simple_dummy_events.o

drivers/staging/iio/ring_sw.c

@@ -1,366 +0,0 @@
-/* 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 <linux/iio/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 indicate 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)
-{
-	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)
-{
-	struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
-	return iio_store_to_sw_ring(ring, data);
-}
-
-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",
-};
-
-static 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,
-};
-
-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;
-	buf->access = &ring_sw_access_funcs;
-
-	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);
-
-MODULE_DESCRIPTION("Industrial I/O software ring buffer");
-MODULE_LICENSE("GPL");

drivers/staging/iio/ring_sw.h

@@ -1,30 +0,0 @@
-/* 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.
- *
- * This code is deliberately kept separate from the main industrialio I/O core
- * as it is intended that in the future a number of different software ring
- * buffer implementations will exist with different characteristics to suit
- * different applications.
- *
- * This particular one was designed for a data capture application where it was
- * particularly important that no userspace reads would interrupt the capture
- * process. To this end the ring is not locked during a read.
- *
- * Comments on this buffer design welcomed. It's far from efficient and some of
- * my understanding of the effects of scheduling on this are somewhat limited.
- * Frankly, to my mind, this is the current weak point in the industrial I/O
- * patch set.
- */
-
-#ifndef _IIO_RING_SW_H_
-#define _IIO_RING_SW_H_
-#include <linux/iio/buffer.h>
-
-struct iio_buffer *iio_sw_rb_allocate(struct iio_dev *indio_dev);
-void iio_sw_rb_free(struct iio_buffer *ring);
-#endif /* _IIO_RING_SW_H_ */