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