drivers/staging/iio/ring_sw.c

   1 /* The industrial I/O simple minimally locked ring buffer.
   2  *
   3  * Copyright (c) 2008 Jonathan Cameron
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 as published by
   7  * the Free Software Foundation.
   8  */
   9
  10 #include <linux/slab.h>
  11 #include <linux/kernel.h>
  12 #include <linux/module.h>
  13 #include <linux/device.h>
  14 #include <linux/workqueue.h>
  15 #include "ring_sw.h"
  16
  17 static inline int __iio_init_sw_ring_buffer(struct iio_sw_ring_buffer *ring,
  18                                             int bytes_per_datum, int length)
  19 {
  20         if ((length == 0) || (bytes_per_datum == 0))
  21                 return -EINVAL;
  22
  23         __iio_init_ring_buffer(&ring->buf, bytes_per_datum, length);
  24         spin_lock_init(&ring->use_lock);
  25         ring->data = kmalloc(length*ring->buf.bpd, GFP_KERNEL);
  26         ring->read_p = 0;
  27         ring->write_p = 0;
  28         ring->last_written_p = 0;
  29         ring->half_p = 0;
  30         return ring->data ? 0 : -ENOMEM;
  31 }
  32
  33 static inline void __iio_free_sw_ring_buffer(struct iio_sw_ring_buffer *ring)
  34 {
  35         kfree(ring->data);
  36 }
  37
  38 void iio_mark_sw_rb_in_use(struct iio_ring_buffer *r)
  39 {
  40         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  41         spin_lock(&ring->use_lock);
  42         ring->use_count++;
  43         spin_unlock(&ring->use_lock);
  44 }
  45 EXPORT_SYMBOL(iio_mark_sw_rb_in_use);
  46
  47 void iio_unmark_sw_rb_in_use(struct iio_ring_buffer *r)
  48 {
  49         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
  50         spin_lock(&ring->use_lock);
  51         ring->use_count--;
  52         spin_unlock(&ring->use_lock);
  53 }
  54 EXPORT_SYMBOL(iio_unmark_sw_rb_in_use);
  55
  56
  57 /* Ring buffer related functionality */
  58 /* Store to ring is typically called in the bh of a data ready interrupt handler
  59  * in the device driver */
  60 /* Lock always held if their is a chance this may be called */
  61 /* Only one of these per ring may run concurrently - enforced by drivers */
  62 int iio_store_to_sw_ring(struct iio_sw_ring_buffer *ring,
  63                          unsigned char *data,
  64                          s64 timestamp)
  65 {
  66         int ret = 0;
  67         int code;
  68         unsigned char *temp_ptr, *change_test_ptr;
  69
  70         /* initial store */
  71         if (unlikely(ring->write_p == 0)) {
  72                 ring->write_p = ring->data;
  73                 /* Doesn't actually matter if this is out of the set
  74                  * as long as the read pointer is valid before this
  75                  * passes it - guaranteed as set later in this function.
  76                  */
  77                 ring->half_p = ring->data - ring->buf.length*ring->buf.bpd/2;
  78         }
  79         /* Copy data to where ever the current write pointer says */
  80         memcpy(ring->write_p, data, ring->buf.bpd);
  81         barrier();
  82         /* Update the pointer used to get most recent value.
  83          * Always valid as either points to latest or second latest value.
  84          * Before this runs it is null and read attempts fail with -EAGAIN.
  85          */
  86         ring->last_written_p = ring->write_p;
  87         barrier();
  88         /* temp_ptr used to ensure we never have an invalid pointer
  89          * it may be slightly lagging, but never invalid
  90          */
  91         temp_ptr = ring->write_p + ring->buf.bpd;
  92         /* End of ring, back to the beginning */
  93         if (temp_ptr == ring->data + ring->buf.length*ring->buf.bpd)
  94                 temp_ptr = ring->data;
  95         /* Update the write pointer
  96          * always valid as long as this is the only function able to write.
  97          * Care needed with smp systems to ensure more than one ring fill
  98          * is never scheduled.
  99          */
 100         ring->write_p = temp_ptr;
 101
 102         if (ring->read_p == 0)
 103                 ring->read_p = ring->data;
 104         /* Buffer full - move the read pointer and create / escalate
 105          * ring event */
 106         /* Tricky case - if the read pointer moves before we adjust it.
 107          * Handle by not pushing if it has moved - may result in occasional
 108          * unnecessary buffer full events when it wasn't quite true.
 109          */
 110         else if (ring->write_p == ring->read_p) {
 111                 change_test_ptr = ring->read_p;
 112                 temp_ptr = change_test_ptr + ring->buf.bpd;
 113                 if (temp_ptr
 114                     == ring->data + ring->buf.length*ring->buf.bpd) {
 115                         temp_ptr = ring->data;
 116                 }
 117                 /* We are moving pointer on one because the ring is full.  Any
 118                  * change to the read pointer will be this or greater.
 119                  */
 120                 if (change_test_ptr == ring->read_p)
 121                         ring->read_p = temp_ptr;
 122
 123                 spin_lock(&ring->buf.shared_ev_pointer.lock);
 124
 125                 ret = iio_push_or_escallate_ring_event(&ring->buf,
 126                                                        IIO_EVENT_CODE_RING_100_FULL,
 127                                                        timestamp);
 128                 spin_unlock(&ring->buf.shared_ev_pointer.lock);
 129                 if (ret)
 130                         goto error_ret;
 131         }
 132         /* investigate if our event barrier has been passed */
 133         /* There are definite 'issues' with this and chances of
 134          * simultaneous read */
 135         /* Also need to use loop count to ensure this only happens once */
 136         ring->half_p += ring->buf.bpd;
 137         if (ring->half_p == ring->data + ring->buf.length*ring->buf.bpd)
 138                 ring->half_p = ring->data;
 139         if (ring->half_p == ring->read_p) {
 140                 spin_lock(&ring->buf.shared_ev_pointer.lock);
 141                 code = IIO_EVENT_CODE_RING_50_FULL;
 142                 ret = __iio_push_event(&ring->buf.ev_int,
 143                                        code,
 144                                        timestamp,
 145                                        &ring->buf.shared_ev_pointer);
 146                 spin_unlock(&ring->buf.shared_ev_pointer.lock);
 147         }
 148 error_ret:
 149         return ret;
 150 }
 151
 152 int iio_rip_sw_rb(struct iio_ring_buffer *r,
 153                   size_t count, u8 **data, int *dead_offset)
 154 {
 155         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
 156
 157         u8 *initial_read_p, *initial_write_p, *current_read_p, *end_read_p;
 158         int ret, max_copied;
 159         int bytes_to_rip;
 160
 161         /* A userspace program has probably made an error if it tries to
 162          *  read something that is not a whole number of bpds.
 163          * Return an error.
 164          */
 165         if (count % ring->buf.bpd) {
 166                 ret = -EINVAL;
 167                 printk(KERN_INFO "Ring buffer read request not whole number of"
 168                        "samples: Request bytes %zd, Current bpd %d\n",
 169                        count, ring->buf.bpd);
 170                 goto error_ret;
 171         }
 172         /* Limit size to whole of ring buffer */
 173         bytes_to_rip = min((size_t)(ring->buf.bpd*ring->buf.length), count);
 174
 175         *data = kmalloc(bytes_to_rip, GFP_KERNEL);
 176         if (*data == NULL) {
 177                 ret = -ENOMEM;
 178                 goto error_ret;
 179         }
 180
 181         /* build local copy */
 182         initial_read_p = ring->read_p;
 183         if (unlikely(initial_read_p == 0)) { /* No data here as yet */
 184                 ret = 0;
 185                 goto error_free_data_cpy;
 186         }
 187
 188         initial_write_p = ring->write_p;
 189
 190         /* Need a consistent pair */
 191         while ((initial_read_p != ring->read_p)
 192                || (initial_write_p != ring->write_p)) {
 193                 initial_read_p = ring->read_p;
 194                 initial_write_p = ring->write_p;
 195         }
 196         if (initial_write_p == initial_read_p) {
 197                 /* No new data available.*/
 198                 ret = 0;
 199                 goto error_free_data_cpy;
 200         }
 201
 202         if (initial_write_p >= initial_read_p + bytes_to_rip) {
 203                 /* write_p is greater than necessary, all is easy */
 204                 max_copied = bytes_to_rip;
 205                 memcpy(*data, initial_read_p, max_copied);
 206                 end_read_p = initial_read_p + max_copied;
 207         } else if (initial_write_p > initial_read_p) {
 208                 /*not enough data to cpy */
 209                 max_copied = initial_write_p - initial_read_p;
 210                 memcpy(*data, initial_read_p, max_copied);
 211                 end_read_p = initial_write_p;
 212         } else {
 213                 /* going through 'end' of ring buffer */
 214                 max_copied = ring->data
 215                         + ring->buf.length*ring->buf.bpd - initial_read_p;
 216                 memcpy(*data, initial_read_p, max_copied);
 217                 /* possible we are done if we align precisely with end */
 218                 if (max_copied == bytes_to_rip)
 219                         end_read_p = ring->data;
 220                 else if (initial_write_p
 221                          > ring->data + bytes_to_rip - max_copied) {
 222                         /* enough data to finish */
 223                         memcpy(*data + max_copied, ring->data,
 224                                bytes_to_rip - max_copied);
 225                         max_copied = bytes_to_rip;
 226                         end_read_p = ring->data + (bytes_to_rip - max_copied);
 227                 } else {  /* not enough data */
 228                         memcpy(*data + max_copied, ring->data,
 229                                initial_write_p - ring->data);
 230                         max_copied += initial_write_p - ring->data;
 231                         end_read_p = initial_write_p;
 232                 }
 233         }
 234         /* Now to verify which section was cleanly copied - i.e. how far
 235          * read pointer has been pushed */
 236         current_read_p = ring->read_p;
 237
 238         if (initial_read_p <= current_read_p)
 239                 *dead_offset = current_read_p - initial_read_p;
 240         else
 241                 *dead_offset = ring->buf.length*ring->buf.bpd
 242                         - (initial_read_p - current_read_p);
 243
 244         /* possible issue if the initial write has been lapped or indeed
 245          * the point we were reading to has been passed */
 246         /* No valid data read.
 247          * In this case the read pointer is already correct having been
 248          * pushed further than we would look. */
 249         if (max_copied - *dead_offset < 0) {
 250                 ret = 0;
 251                 goto error_free_data_cpy;
 252         }
 253
 254         /* setup the next read position */
 255         /* Beware, this may fail due to concurrency fun and games.
 256          *  Possible that sufficient fill commands have run to push the read
 257          * pointer past where we would be after the rip. If this occurs, leave
 258          * it be.
 259          */
 260         /* Tricky - deal with loops */
 261
 262         while (ring->read_p != end_read_p)
 263                 ring->read_p = end_read_p;
 264
 265         return max_copied - *dead_offset;
 266
 267 error_free_data_cpy:
 268         kfree(*data);
 269 error_ret:
 270         return ret;
 271 }
 272 EXPORT_SYMBOL(iio_rip_sw_rb);
 273
 274 int iio_store_to_sw_rb(struct iio_ring_buffer *r, u8 *data, s64 timestamp)
 275 {
 276         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
 277         return iio_store_to_sw_ring(ring, data, timestamp);
 278 }
 279 EXPORT_SYMBOL(iio_store_to_sw_rb);
 280
 281 int iio_read_last_from_sw_ring(struct iio_sw_ring_buffer *ring,
 282                                unsigned char *data)
 283 {
 284         unsigned char *last_written_p_copy;
 285
 286         iio_mark_sw_rb_in_use(&ring->buf);
 287 again:
 288         barrier();
 289         last_written_p_copy = ring->last_written_p;
 290         barrier(); /*unnessecary? */
 291         /* Check there is anything here */
 292         if (last_written_p_copy == 0)
 293                 return -EAGAIN;
 294         memcpy(data, last_written_p_copy, ring->buf.bpd);
 295
 296         if (unlikely(ring->last_written_p != last_written_p_copy))
 297                 goto again;
 298
 299         iio_unmark_sw_rb_in_use(&ring->buf);
 300         return 0;
 301 }
 302
 303 int iio_read_last_from_sw_rb(struct iio_ring_buffer *r,
 304                              unsigned char *data)
 305 {
 306         return iio_read_last_from_sw_ring(iio_to_sw_ring(r), data);
 307 }
 308 EXPORT_SYMBOL(iio_read_last_from_sw_rb);
 309
 310 int iio_request_update_sw_rb(struct iio_ring_buffer *r)
 311 {
 312         int ret = 0;
 313         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
 314
 315         spin_lock(&ring->use_lock);
 316         if (!ring->update_needed)
 317                 goto error_ret;
 318         if (ring->use_count) {
 319                 ret = -EAGAIN;
 320                 goto error_ret;
 321         }
 322         __iio_free_sw_ring_buffer(ring);
 323         ret = __iio_init_sw_ring_buffer(ring, ring->buf.bpd, ring->buf.length);
 324 error_ret:
 325         spin_unlock(&ring->use_lock);
 326         return ret;
 327 }
 328 EXPORT_SYMBOL(iio_request_update_sw_rb);
 329
 330 int iio_get_bpd_sw_rb(struct iio_ring_buffer *r)
 331 {
 332         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
 333         return ring->buf.bpd;
 334 }
 335 EXPORT_SYMBOL(iio_get_bpd_sw_rb);
 336
 337 int iio_set_bpd_sw_rb(struct iio_ring_buffer *r, size_t bpd)
 338 {
 339         if (r->bpd != bpd) {
 340                 r->bpd = bpd;
 341                 if (r->access.mark_param_change)
 342                         r->access.mark_param_change(r);
 343         }
 344         return 0;
 345 }
 346 EXPORT_SYMBOL(iio_set_bpd_sw_rb);
 347
 348 int iio_get_length_sw_rb(struct iio_ring_buffer *r)
 349 {
 350         return r->length;
 351 }
 352 EXPORT_SYMBOL(iio_get_length_sw_rb);
 353
 354 int iio_set_length_sw_rb(struct iio_ring_buffer *r, int length)
 355 {
 356         if (r->length != length) {
 357                 r->length = length;
 358                 if (r->access.mark_param_change)
 359                         r->access.mark_param_change(r);
 360         }
 361         return 0;
 362 }
 363 EXPORT_SYMBOL(iio_set_length_sw_rb);
 364
 365 int iio_mark_update_needed_sw_rb(struct iio_ring_buffer *r)
 366 {
 367         struct iio_sw_ring_buffer *ring = iio_to_sw_ring(r);
 368         ring->update_needed = true;
 369         return 0;
 370 }
 371 EXPORT_SYMBOL(iio_mark_update_needed_sw_rb);
 372
 373 static void iio_sw_rb_release(struct device *dev)
 374 {
 375         struct iio_ring_buffer *r = to_iio_ring_buffer(dev);
 376         kfree(iio_to_sw_ring(r));
 377 }
 378
 379 static IIO_RING_ENABLE_ATTR;
 380 static IIO_RING_BPS_ATTR;
 381 static IIO_RING_LENGTH_ATTR;
 382
 383 /* Standard set of ring buffer attributes */
 384 static struct attribute *iio_ring_attributes[] = {
 385         &dev_attr_length.attr,
 386         &dev_attr_bps.attr,
 387         &dev_attr_ring_enable.attr,
 388         NULL,
 389 };
 390
 391 static struct attribute_group iio_ring_attribute_group = {
 392         .attrs = iio_ring_attributes,
 393 };
 394
 395 static const struct attribute_group *iio_ring_attribute_groups[] = {
 396         &iio_ring_attribute_group,
 397         NULL
 398 };
 399
 400 static struct device_type iio_sw_ring_type = {
 401         .release = iio_sw_rb_release,
 402         .groups = iio_ring_attribute_groups,
 403 };
 404
 405 struct iio_ring_buffer *iio_sw_rb_allocate(struct iio_dev *indio_dev)
 406 {
 407         struct iio_ring_buffer *buf;
 408         struct iio_sw_ring_buffer *ring;
 409
 410         ring = kzalloc(sizeof *ring, GFP_KERNEL);
 411         if (!ring)
 412                 return 0;
 413         buf = &ring->buf;
 414
 415         iio_ring_buffer_init(buf, indio_dev);
 416         buf->dev.type = &iio_sw_ring_type;
 417         device_initialize(&buf->dev);
 418         buf->dev.parent = &indio_dev->dev;
 419         buf->dev.class = &iio_class;
 420         dev_set_drvdata(&buf->dev, (void *)buf);
 421
 422         return buf;
 423 }
 424 EXPORT_SYMBOL(iio_sw_rb_allocate);
 425
 426 void iio_sw_rb_free(struct iio_ring_buffer *r)
 427 {
 428         if (r)
 429                 iio_put_ring_buffer(r);
 430 }
 431 EXPORT_SYMBOL(iio_sw_rb_free);
 432 MODULE_DESCRIPTION("Industrialio I/O software ring buffer");
 433 MODULE_LICENSE("GPL");