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