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 #define SPI_BITBANG_CS_DELAY    100
  28
  29
  30 /*----------------------------------------------------------------------*/
  31
  32 /*
  33  * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
  34  * Use this for GPIO or shift-register level hardware APIs.
  35  *
  36  * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
  37  * to glue code.  These bitbang setup() and cleanup() routines are always
  38  * used, though maybe they're called from controller-aware code.
  39  *
  40  * chipselect() and friends may use spi_device->controller_data and
  41  * controller registers as appropriate.
  42  *
  43  *
  44  * NOTE:  SPI controller pins can often be used as GPIO pins instead,
  45  * which means you could use a bitbang driver either to get hardware
  46  * working quickly, or testing for differences that aren't speed related.
  47  */
  48
  49 struct spi_bitbang_cs {
  50         unsigned        nsecs;  /* (clock cycle time)/2 */
  51         u32             (*txrx_word)(struct spi_device *spi, unsigned nsecs,
  52                                         u32 word, u8 bits, unsigned flags);
  53         unsigned        (*txrx_bufs)(struct spi_device *,
  54                                         u32 (*txrx_word)(
  55                                                 struct spi_device *spi,
  56                                                 unsigned nsecs,
  57                                                 u32 word, u8 bits,
  58                                                 unsigned flags),
  59                                         unsigned, struct spi_transfer *,
  60                                         unsigned);
  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 flags),
  69         unsigned                ns,
  70         struct spi_transfer     *t,
  71         unsigned flags
  72 ) {
  73         unsigned                bits = t->bits_per_word;
  74         unsigned                count = t->len;
  75         const u8                *tx = t->tx_buf;
  76         u8                      *rx = t->rx_buf;
  77
  78         while (likely(count > 0)) {
  79                 u8              word = 0;
  80
  81                 if (tx)
  82                         word = *tx++;
  83                 word = txrx_word(spi, ns, word, bits, flags);
  84                 if (rx)
  85                         *rx++ = word;
  86                 count -= 1;
  87         }
  88         return t->len - count;
  89 }
  90
  91 static unsigned bitbang_txrx_16(
  92         struct spi_device       *spi,
  93         u32                     (*txrx_word)(struct spi_device *spi,
  94                                         unsigned nsecs,
  95                                         u32 word, u8 bits,
  96                                         unsigned flags),
  97         unsigned                ns,
  98         struct spi_transfer     *t,
  99         unsigned flags
 100 ) {
 101         unsigned                bits = t->bits_per_word;
 102         unsigned                count = t->len;
 103         const u16               *tx = t->tx_buf;
 104         u16                     *rx = t->rx_buf;
 105
 106         while (likely(count > 1)) {
 107                 u16             word = 0;
 108
 109                 if (tx)
 110                         word = *tx++;
 111                 word = txrx_word(spi, ns, word, bits, flags);
 112                 if (rx)
 113                         *rx++ = word;
 114                 count -= 2;
 115         }
 116         return t->len - count;
 117 }
 118
 119 static unsigned bitbang_txrx_32(
 120         struct spi_device       *spi,
 121         u32                     (*txrx_word)(struct spi_device *spi,
 122                                         unsigned nsecs,
 123                                         u32 word, u8 bits,
 124                                         unsigned flags),
 125         unsigned                ns,
 126         struct spi_transfer     *t,
 127         unsigned flags
 128 ) {
 129         unsigned                bits = t->bits_per_word;
 130         unsigned                count = t->len;
 131         const u32               *tx = t->tx_buf;
 132         u32                     *rx = t->rx_buf;
 133
 134         while (likely(count > 3)) {
 135                 u32             word = 0;
 136
 137                 if (tx)
 138                         word = *tx++;
 139                 word = txrx_word(spi, ns, word, bits, flags);
 140                 if (rx)
 141                         *rx++ = word;
 142                 count -= 4;
 143         }
 144         return t->len - count;
 145 }
 146
 147 int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 148 {
 149         struct spi_bitbang_cs   *cs = spi->controller_state;
 150         u8                      bits_per_word;
 151         u32                     hz;
 152
 153         if (t) {
 154                 bits_per_word = t->bits_per_word;
 155                 hz = t->speed_hz;
 156         } else {
 157                 bits_per_word = 0;
 158                 hz = 0;
 159         }
 160
 161         /* spi_transfer level calls that work per-word */
 162         if (!bits_per_word)
 163                 bits_per_word = spi->bits_per_word;
 164         if (bits_per_word <= 8)
 165                 cs->txrx_bufs = bitbang_txrx_8;
 166         else if (bits_per_word <= 16)
 167                 cs->txrx_bufs = bitbang_txrx_16;
 168         else if (bits_per_word <= 32)
 169                 cs->txrx_bufs = bitbang_txrx_32;
 170         else
 171                 return -EINVAL;
 172
 173         /* nsecs = (clock period)/2 */
 174         if (!hz)
 175                 hz = spi->max_speed_hz;
 176         if (hz) {
 177                 cs->nsecs = (1000000000/2) / hz;
 178                 if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
 179                         return -EINVAL;
 180         }
 181
 182         return 0;
 183 }
 184 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
 185
 186 /**
 187  * spi_bitbang_setup - default setup for per-word I/O loops
 188  */
 189 int spi_bitbang_setup(struct spi_device *spi)
 190 {
 191         struct spi_bitbang_cs   *cs = spi->controller_state;
 192         struct spi_bitbang      *bitbang;
 193
 194         bitbang = spi_master_get_devdata(spi->master);
 195
 196         if (!cs) {
 197                 cs = kzalloc(sizeof(*cs), GFP_KERNEL);
 198                 if (!cs)
 199                         return -ENOMEM;
 200                 spi->controller_state = cs;
 201         }
 202
 203         /* per-word shift register access, in hardware or bitbanging */
 204         cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 205         if (!cs->txrx_word)
 206                 return -EINVAL;
 207
 208         if (bitbang->setup_transfer) {
 209                 int retval = bitbang->setup_transfer(spi, NULL);
 210                 if (retval < 0)
 211                         return retval;
 212         }
 213
 214         dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);
 215
 216         /* NOTE we _need_ to call chipselect() early, ideally with adapter
 217          * setup, unless the hardware defaults cooperate to avoid confusion
 218          * between normal (active low) and inverted chipselects.
 219          */
 220
 221         /* deselect chip (low or high) */
 222         mutex_lock(&bitbang->lock);
 223         if (!bitbang->busy) {
 224                 bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 225                 ndelay(cs->nsecs);
 226         }
 227         mutex_unlock(&bitbang->lock);
 228
 229         return 0;
 230 }
 231 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 232
 233 /**
 234  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 235  */
 236 void spi_bitbang_cleanup(struct spi_device *spi)
 237 {
 238         kfree(spi->controller_state);
 239 }
 240 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 241
 242 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 243 {
 244         struct spi_bitbang_cs   *cs = spi->controller_state;
 245         unsigned                nsecs = cs->nsecs;
 246         struct spi_bitbang      *bitbang;
 247
 248         bitbang = spi_master_get_devdata(spi->master);
 249         if (bitbang->set_line_direction) {
 250                 int err;
 251
 252                 err = bitbang->set_line_direction(spi, !!(t->tx_buf));
 253                 if (err < 0)
 254                         return err;
 255         }
 256
 257         if (spi->mode & SPI_3WIRE) {
 258                 unsigned flags;
 259
 260                 flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX;
 261                 return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
 262         }
 263         return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
 264 }
 265
 266 /*----------------------------------------------------------------------*/
 267
 268 /*
 269  * SECOND PART ... simple transfer queue runner.
 270  *
 271  * This costs a task context per controller, running the queue by
 272  * performing each transfer in sequence.  Smarter hardware can queue
 273  * several DMA transfers at once, and process several controller queues
 274  * in parallel; this driver doesn't match such hardware very well.
 275  *
 276  * Drivers can provide word-at-a-time i/o primitives, or provide
 277  * transfer-at-a-time ones to leverage dma or fifo hardware.
 278  */
 279
 280 static int spi_bitbang_prepare_hardware(struct spi_master *spi)
 281 {
 282         struct spi_bitbang      *bitbang;
 283
 284         bitbang = spi_master_get_devdata(spi);
 285
 286         mutex_lock(&bitbang->lock);
 287         bitbang->busy = 1;
 288         mutex_unlock(&bitbang->lock);
 289
 290         return 0;
 291 }
 292
 293 static int spi_bitbang_transfer_one(struct spi_master *master,
 294                                     struct spi_device *spi,
 295                                     struct spi_transfer *transfer)
 296 {
 297         struct spi_bitbang *bitbang = spi_master_get_devdata(master);
 298         int status = 0;
 299
 300         if (bitbang->setup_transfer) {
 301                 status = bitbang->setup_transfer(spi, transfer);
 302                 if (status < 0)
 303                         goto out;
 304         }
 305
 306         if (transfer->len)
 307                 status = bitbang->txrx_bufs(spi, transfer);
 308
 309         if (status == transfer->len)
 310                 status = 0;
 311         else if (status >= 0)
 312                 status = -EREMOTEIO;
 313
 314 out:
 315         spi_finalize_current_transfer(master);
 316
 317         return status;
 318 }
 319
 320 static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
 321 {
 322         struct spi_bitbang      *bitbang;
 323
 324         bitbang = spi_master_get_devdata(spi);
 325
 326         mutex_lock(&bitbang->lock);
 327         bitbang->busy = 0;
 328         mutex_unlock(&bitbang->lock);
 329
 330         return 0;
 331 }
 332
 333 static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
 334 {
 335         struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master);
 336
 337         /* SPI core provides CS high / low, but bitbang driver
 338          * expects CS active
 339          * spi device driver takes care of handling SPI_CS_HIGH
 340          */
 341         enable = (!!(spi->mode & SPI_CS_HIGH) == enable);
 342
 343         ndelay(SPI_BITBANG_CS_DELAY);
 344         bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
 345                             BITBANG_CS_INACTIVE);
 346         ndelay(SPI_BITBANG_CS_DELAY);
 347 }
 348
 349 /*----------------------------------------------------------------------*/
 350
 351 /**
 352  * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 353  * @bitbang: driver handle
 354  *
 355  * Caller should have zero-initialized all parts of the structure, and then
 356  * provided callbacks for chip selection and I/O loops.  If the master has
 357  * a transfer method, its final step should call spi_bitbang_transfer; or,
 358  * that's the default if the transfer routine is not initialized.  It should
 359  * also set up the bus number and number of chipselects.
 360  *
 361  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 362  * hardware that basically exposes a shift register) or per-spi_transfer
 363  * (which takes better advantage of hardware like fifos or DMA engines).
 364  *
 365  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
 366  * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
 367  * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 368  * routine isn't initialized.
 369  *
 370  * This routine registers the spi_master, which will process requests in a
 371  * dedicated task, keeping IRQs unblocked most of the time.  To stop
 372  * processing those requests, call spi_bitbang_stop().
 373  *
 374  * On success, this routine will take a reference to master. The caller is
 375  * responsible for calling spi_bitbang_stop() to decrement the reference and
 376  * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory
 377  * leak.
 378  */
 379 int spi_bitbang_start(struct spi_bitbang *bitbang)
 380 {
 381         struct spi_master *master = bitbang->master;
 382         int ret;
 383
 384         if (!master || !bitbang->chipselect)
 385                 return -EINVAL;
 386
 387         mutex_init(&bitbang->lock);
 388
 389         if (!master->mode_bits)
 390                 master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
 391
 392         if (master->transfer || master->transfer_one_message)
 393                 return -EINVAL;
 394
 395         master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
 396         master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
 397         master->transfer_one = spi_bitbang_transfer_one;
 398         master->set_cs = spi_bitbang_set_cs;
 399
 400         if (!bitbang->txrx_bufs) {
 401                 bitbang->use_dma = 0;
 402                 bitbang->txrx_bufs = spi_bitbang_bufs;
 403                 if (!master->setup) {
 404                         if (!bitbang->setup_transfer)
 405                                 bitbang->setup_transfer =
 406                                          spi_bitbang_setup_transfer;
 407                         master->setup = spi_bitbang_setup;
 408                         master->cleanup = spi_bitbang_cleanup;
 409                 }
 410         }
 411
 412         /* driver may get busy before register() returns, especially
 413          * if someone registered boardinfo for devices
 414          */
 415         ret = spi_register_master(spi_master_get(master));
 416         if (ret)
 417                 spi_master_put(master);
 418
 419         return ret;
 420 }
 421 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 422
 423 /**
 424  * spi_bitbang_stop - stops the task providing spi communication
 425  */
 426 void spi_bitbang_stop(struct spi_bitbang *bitbang)
 427 {
 428         spi_unregister_master(bitbang->master);
 429 }
 430 EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 431
 432 MODULE_LICENSE("GPL");
 433