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