drivers/spi/spi_bitbang.c

   1 /*
   2  * spi_bitbang.c - polling/bitbanging SPI master controller driver utilities
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17  */
  18
  19 #include <linux/init.h>
  20 #include <linux/spinlock.h>
  21 #include <linux/workqueue.h>
  22 #include <linux/interrupt.h>
  23 #include <linux/delay.h>
  24 #include <linux/errno.h>
  25 #include <linux/platform_device.h>
  26
  27 #include <linux/spi/spi.h>
  28 #include <linux/spi/spi_bitbang.h>
  29
  30
  31 /*----------------------------------------------------------------------*/
  32
  33 /*
  34  * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
  35  * Use this for GPIO or shift-register level hardware APIs.
  36  *
  37  * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
  38  * to glue code.  These bitbang setup() and cleanup() routines are always
  39  * used, though maybe they're called from controller-aware code.
  40  *
  41  * chipselect() and friends may use use spi_device->controller_data and
  42  * controller registers as appropriate.
  43  *
  44  *
  45  * NOTE:  SPI controller pins can often be used as GPIO pins instead,
  46  * which means you could use a bitbang driver either to get hardware
  47  * working quickly, or testing for differences that aren't speed related.
  48  */
  49
  50 struct spi_bitbang_cs {
  51         unsigned        nsecs;  /* (clock cycle time)/2 */
  52         u32             (*txrx_word)(struct spi_device *spi, unsigned nsecs,
  53                                         u32 word, u8 bits);
  54         unsigned        (*txrx_bufs)(struct spi_device *,
  55                                         u32 (*txrx_word)(
  56                                                 struct spi_device *spi,
  57                                                 unsigned nsecs,
  58                                                 u32 word, u8 bits),
  59                                         unsigned, struct spi_transfer *);
  60 };
  61
  62 static unsigned bitbang_txrx_8(
  63         struct spi_device       *spi,
  64         u32                     (*txrx_word)(struct spi_device *spi,
  65                                         unsigned nsecs,
  66                                         u32 word, u8 bits),
  67         unsigned                ns,
  68         struct spi_transfer     *t
  69 ) {
  70         unsigned                bits = spi->bits_per_word;
  71         unsigned                count = t->len;
  72         const u8                *tx = t->tx_buf;
  73         u8                      *rx = t->rx_buf;
  74
  75         while (likely(count > 0)) {
  76                 u8              word = 0;
  77
  78                 if (tx)
  79                         word = *tx++;
  80                 word = txrx_word(spi, ns, word, bits);
  81                 if (rx)
  82                         *rx++ = word;
  83                 count -= 1;
  84         }
  85         return t->len - count;
  86 }
  87
  88 static unsigned bitbang_txrx_16(
  89         struct spi_device       *spi,
  90         u32                     (*txrx_word)(struct spi_device *spi,
  91                                         unsigned nsecs,
  92                                         u32 word, u8 bits),
  93         unsigned                ns,
  94         struct spi_transfer     *t
  95 ) {
  96         unsigned                bits = spi->bits_per_word;
  97         unsigned                count = t->len;
  98         const u16               *tx = t->tx_buf;
  99         u16                     *rx = t->rx_buf;
 100
 101         while (likely(count > 1)) {
 102                 u16             word = 0;
 103
 104                 if (tx)
 105                         word = *tx++;
 106                 word = txrx_word(spi, ns, word, bits);
 107                 if (rx)
 108                         *rx++ = word;
 109                 count -= 2;
 110         }
 111         return t->len - count;
 112 }
 113
 114 static unsigned bitbang_txrx_32(
 115         struct spi_device       *spi,
 116         u32                     (*txrx_word)(struct spi_device *spi,
 117                                         unsigned nsecs,
 118                                         u32 word, u8 bits),
 119         unsigned                ns,
 120         struct spi_transfer     *t
 121 ) {
 122         unsigned                bits = spi->bits_per_word;
 123         unsigned                count = t->len;
 124         const u32               *tx = t->tx_buf;
 125         u32                     *rx = t->rx_buf;
 126
 127         while (likely(count > 3)) {
 128                 u32             word = 0;
 129
 130                 if (tx)
 131                         word = *tx++;
 132                 word = txrx_word(spi, ns, word, bits);
 133                 if (rx)
 134                         *rx++ = word;
 135                 count -= 4;
 136         }
 137         return t->len - count;
 138 }
 139
 140 int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 141 {
 142         struct spi_bitbang_cs   *cs = spi->controller_state;
 143         u8                      bits_per_word;
 144         u32                     hz;
 145
 146         if (t) {
 147                 bits_per_word = t->bits_per_word;
 148                 hz = t->speed_hz;
 149         } else {
 150                 bits_per_word = 0;
 151                 hz = 0;
 152         }
 153
 154         /* spi_transfer level calls that work per-word */
 155         if (!bits_per_word)
 156                 bits_per_word = spi->bits_per_word;
 157         if (bits_per_word <= 8)
 158                 cs->txrx_bufs = bitbang_txrx_8;
 159         else if (bits_per_word <= 16)
 160                 cs->txrx_bufs = bitbang_txrx_16;
 161         else if (bits_per_word <= 32)
 162                 cs->txrx_bufs = bitbang_txrx_32;
 163         else
 164                 return -EINVAL;
 165
 166         /* nsecs = (clock period)/2 */
 167         if (!hz)
 168                 hz = spi->max_speed_hz;
 169         if (hz) {
 170                 cs->nsecs = (1000000000/2) / hz;
 171                 if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
 172                         return -EINVAL;
 173         }
 174
 175         return 0;
 176 }
 177 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
 178
 179 /**
 180  * spi_bitbang_setup - default setup for per-word I/O loops
 181  */
 182 int spi_bitbang_setup(struct spi_device *spi)
 183 {
 184         struct spi_bitbang_cs   *cs = spi->controller_state;
 185         struct spi_bitbang      *bitbang;
 186         int                     retval;
 187         unsigned long           flags;
 188
 189         bitbang = spi_master_get_devdata(spi->master);
 190
 191         /* Bitbangers can support SPI_CS_HIGH, SPI_3WIRE, and so on;
 192          * add those to master->flags, and provide the other support.
 193          */
 194         if ((spi->mode & ~(SPI_CPOL|SPI_CPHA|bitbang->flags)) != 0)
 195                 return -EINVAL;
 196
 197         if (!cs) {
 198                 cs = kzalloc(sizeof *cs, GFP_KERNEL);
 199                 if (!cs)
 200                         return -ENOMEM;
 201                 spi->controller_state = cs;
 202         }
 203
 204         if (!spi->bits_per_word)
 205                 spi->bits_per_word = 8;
 206
 207         /* per-word shift register access, in hardware or bitbanging */
 208         cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 209         if (!cs->txrx_word)
 210                 return -EINVAL;
 211
 212         retval = bitbang->setup_transfer(spi, NULL);
 213         if (retval < 0)
 214                 return retval;
 215
 216         dev_dbg(&spi->dev, "%s, mode %d, %u bits/w, %u nsec/bit\n",
 217                         __func__, spi->mode & (SPI_CPOL | SPI_CPHA),
 218                         spi->bits_per_word, 2 * cs->nsecs);
 219
 220         /* NOTE we _need_ to call chipselect() early, ideally with adapter
 221          * setup, unless the hardware defaults cooperate to avoid confusion
 222          * between normal (active low) and inverted chipselects.
 223          */
 224
 225         /* deselect chip (low or high) */
 226         spin_lock_irqsave(&bitbang->lock, flags);
 227         if (!bitbang->busy) {
 228                 bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 229                 ndelay(cs->nsecs);
 230         }
 231         spin_unlock_irqrestore(&bitbang->lock, flags);
 232
 233         return 0;
 234 }
 235 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 236
 237 /**
 238  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 239  */
 240 void spi_bitbang_cleanup(struct spi_device *spi)
 241 {
 242         kfree(spi->controller_state);
 243 }
 244 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 245
 246 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 247 {
 248         struct spi_bitbang_cs   *cs = spi->controller_state;
 249         unsigned                nsecs = cs->nsecs;
 250
 251         return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t);
 252 }
 253
 254 /*----------------------------------------------------------------------*/
 255
 256 /*
 257  * SECOND PART ... simple transfer queue runner.
 258  *
 259  * This costs a task context per controller, running the queue by
 260  * performing each transfer in sequence.  Smarter hardware can queue
 261  * several DMA transfers at once, and process several controller queues
 262  * in parallel; this driver doesn't match such hardware very well.
 263  *
 264  * Drivers can provide word-at-a-time i/o primitives, or provide
 265  * transfer-at-a-time ones to leverage dma or fifo hardware.
 266  */
 267 static void bitbang_work(struct work_struct *work)
 268 {
 269         struct spi_bitbang      *bitbang =
 270                 container_of(work, struct spi_bitbang, work);
 271         unsigned long           flags;
 272
 273         spin_lock_irqsave(&bitbang->lock, flags);
 274         bitbang->busy = 1;
 275         while (!list_empty(&bitbang->queue)) {
 276                 struct spi_message      *m;
 277                 struct spi_device       *spi;
 278                 unsigned                nsecs;
 279                 struct spi_transfer     *t = NULL;
 280                 unsigned                tmp;
 281                 unsigned                cs_change;
 282                 int                     status;
 283                 int                     (*setup_transfer)(struct spi_device *,
 284                                                 struct spi_transfer *);
 285
 286                 m = container_of(bitbang->queue.next, struct spi_message,
 287                                 queue);
 288                 list_del_init(&m->queue);
 289                 spin_unlock_irqrestore(&bitbang->lock, flags);
 290
 291                 /* FIXME this is made-up ... the correct value is known to
 292                  * word-at-a-time bitbang code, and presumably chipselect()
 293                  * should enforce these requirements too?
 294                  */
 295                 nsecs = 100;
 296
 297                 spi = m->spi;
 298                 tmp = 0;
 299                 cs_change = 1;
 300                 status = 0;
 301                 setup_transfer = NULL;
 302
 303                 list_for_each_entry (t, &m->transfers, transfer_list) {
 304
 305                         /* override or restore speed and wordsize */
 306                         if (t->speed_hz || t->bits_per_word) {
 307                                 setup_transfer = bitbang->setup_transfer;
 308                                 if (!setup_transfer) {
 309                                         status = -ENOPROTOOPT;
 310                                         break;
 311                                 }
 312                         }
 313                         if (setup_transfer) {
 314                                 status = setup_transfer(spi, t);
 315                                 if (status < 0)
 316                                         break;
 317                         }
 318
 319                         /* set up default clock polarity, and activate chip;
 320                          * this implicitly updates clock and spi modes as
 321                          * previously recorded for this device via setup().
 322                          * (and also deselects any other chip that might be
 323                          * selected ...)
 324                          */
 325                         if (cs_change) {
 326                                 bitbang->chipselect(spi, BITBANG_CS_ACTIVE);
 327                                 ndelay(nsecs);
 328                         }
 329                         cs_change = t->cs_change;
 330                         if (!t->tx_buf && !t->rx_buf && t->len) {
 331                                 status = -EINVAL;
 332                                 break;
 333                         }
 334
 335                         /* transfer data.  the lower level code handles any
 336                          * new dma mappings it needs. our caller always gave
 337                          * us dma-safe buffers.
 338                          */
 339                         if (t->len) {
 340                                 /* REVISIT dma API still needs a designated
 341                                  * DMA_ADDR_INVALID; ~0 might be better.
 342                                  */
 343                                 if (!m->is_dma_mapped)
 344                                         t->rx_dma = t->tx_dma = 0;
 345                                 status = bitbang->txrx_bufs(spi, t);
 346                         }
 347                         if (status > 0)
 348                                 m->actual_length += status;
 349                         if (status != t->len) {
 350                                 /* always report some kind of error */
 351                                 if (status >= 0)
 352                                         status = -EREMOTEIO;
 353                                 break;
 354                         }
 355                         status = 0;
 356
 357                         /* protocol tweaks before next transfer */
 358                         if (t->delay_usecs)
 359                                 udelay(t->delay_usecs);
 360
 361                         if (!cs_change)
 362                                 continue;
 363                         if (t->transfer_list.next == &m->transfers)
 364                                 break;
 365
 366                         /* sometimes a short mid-message deselect of the chip
 367                          * may be needed to terminate a mode or command
 368                          */
 369                         ndelay(nsecs);
 370                         bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 371                         ndelay(nsecs);
 372                 }
 373
 374                 m->status = status;
 375                 m->complete(m->context);
 376
 377                 /* restore speed and wordsize */
 378                 if (setup_transfer)
 379                         setup_transfer(spi, NULL);
 380
 381                 /* normally deactivate chipselect ... unless no error and
 382                  * cs_change has hinted that the next message will probably
 383                  * be for this chip too.
 384                  */
 385                 if (!(status == 0 && cs_change)) {
 386                         ndelay(nsecs);
 387                         bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 388                         ndelay(nsecs);
 389                 }
 390
 391                 spin_lock_irqsave(&bitbang->lock, flags);
 392         }
 393         bitbang->busy = 0;
 394         spin_unlock_irqrestore(&bitbang->lock, flags);
 395 }
 396
 397 /**
 398  * spi_bitbang_transfer - default submit to transfer queue
 399  */
 400 int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m)
 401 {
 402         struct spi_bitbang      *bitbang;
 403         unsigned long           flags;
 404         int                     status = 0;
 405
 406         m->actual_length = 0;
 407         m->status = -EINPROGRESS;
 408
 409         bitbang = spi_master_get_devdata(spi->master);
 410
 411         spin_lock_irqsave(&bitbang->lock, flags);
 412         if (!spi->max_speed_hz)
 413                 status = -ENETDOWN;
 414         else {
 415                 list_add_tail(&m->queue, &bitbang->queue);
 416                 queue_work(bitbang->workqueue, &bitbang->work);
 417         }
 418         spin_unlock_irqrestore(&bitbang->lock, flags);
 419
 420         return status;
 421 }
 422 EXPORT_SYMBOL_GPL(spi_bitbang_transfer);
 423
 424 /*----------------------------------------------------------------------*/
 425
 426 /**
 427  * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 428  * @bitbang: driver handle
 429  *
 430  * Caller should have zero-initialized all parts of the structure, and then
 431  * provided callbacks for chip selection and I/O loops.  If the master has
 432  * a transfer method, its final step should call spi_bitbang_transfer; or,
 433  * that's the default if the transfer routine is not initialized.  It should
 434  * also set up the bus number and number of chipselects.
 435  *
 436  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 437  * hardware that basically exposes a shift register) or per-spi_transfer
 438  * (which takes better advantage of hardware like fifos or DMA engines).
 439  *
 440  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
 441  * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
 442  * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 443  * routine isn't initialized.
 444  *
 445  * This routine registers the spi_master, which will process requests in a
 446  * dedicated task, keeping IRQs unblocked most of the time.  To stop
 447  * processing those requests, call spi_bitbang_stop().
 448  */
 449 int spi_bitbang_start(struct spi_bitbang *bitbang)
 450 {
 451         int     status;
 452
 453         if (!bitbang->master || !bitbang->chipselect)
 454                 return -EINVAL;
 455
 456         INIT_WORK(&bitbang->work, bitbang_work);
 457         spin_lock_init(&bitbang->lock);
 458         INIT_LIST_HEAD(&bitbang->queue);
 459
 460         if (!bitbang->master->transfer)
 461                 bitbang->master->transfer = spi_bitbang_transfer;
 462         if (!bitbang->txrx_bufs) {
 463                 bitbang->use_dma = 0;
 464                 bitbang->txrx_bufs = spi_bitbang_bufs;
 465                 if (!bitbang->master->setup) {
 466                         if (!bitbang->setup_transfer)
 467                                 bitbang->setup_transfer =
 468                                          spi_bitbang_setup_transfer;
 469                         bitbang->master->setup = spi_bitbang_setup;
 470                         bitbang->master->cleanup = spi_bitbang_cleanup;
 471                 }
 472         } else if (!bitbang->master->setup)
 473                 return -EINVAL;
 474
 475         /* this task is the only thing to touch the SPI bits */
 476         bitbang->busy = 0;
 477         bitbang->workqueue = create_singlethread_workqueue(
 478                         dev_name(bitbang->master->dev.parent));
 479         if (bitbang->workqueue == NULL) {
 480                 status = -EBUSY;
 481                 goto err1;
 482         }
 483
 484         /* driver may get busy before register() returns, especially
 485          * if someone registered boardinfo for devices
 486          */
 487         status = spi_register_master(bitbang->master);
 488         if (status < 0)
 489                 goto err2;
 490
 491         return status;
 492
 493 err2:
 494         destroy_workqueue(bitbang->workqueue);
 495 err1:
 496         return status;
 497 }
 498 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 499
 500 /**
 501  * spi_bitbang_stop - stops the task providing spi communication
 502  */
 503 int spi_bitbang_stop(struct spi_bitbang *bitbang)
 504 {
 505         spi_unregister_master(bitbang->master);
 506
 507         WARN_ON(!list_empty(&bitbang->queue));
 508
 509         destroy_workqueue(bitbang->workqueue);
 510
 511         return 0;
 512 }
 513 EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 514
 515 MODULE_LICENSE("GPL");
 516