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