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