drivers/spi/spi-bitbang.c

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