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         return 0;
 217 }
 218 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 219
 220 /**
 221  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 222  */
 223 void spi_bitbang_cleanup(struct spi_device *spi)
 224 {
 225         kfree(spi->controller_state);
 226 }
 227 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 228
 229 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 230 {
 231         struct spi_bitbang_cs   *cs = spi->controller_state;
 232         unsigned                nsecs = cs->nsecs;
 233         struct spi_bitbang      *bitbang;
 234
 235         bitbang = spi_master_get_devdata(spi->master);
 236         if (bitbang->set_line_direction) {
 237                 int err;
 238
 239                 err = bitbang->set_line_direction(spi, !!(t->tx_buf));
 240                 if (err < 0)
 241                         return err;
 242         }
 243
 244         if (spi->mode & SPI_3WIRE) {
 245                 unsigned flags;
 246
 247                 flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX;
 248                 return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
 249         }
 250         return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
 251 }
 252
 253 /*----------------------------------------------------------------------*/
 254
 255 /*
 256  * SECOND PART ... simple transfer queue runner.
 257  *
 258  * This costs a task context per controller, running the queue by
 259  * performing each transfer in sequence.  Smarter hardware can queue
 260  * several DMA transfers at once, and process several controller queues
 261  * in parallel; this driver doesn't match such hardware very well.
 262  *
 263  * Drivers can provide word-at-a-time i/o primitives, or provide
 264  * transfer-at-a-time ones to leverage dma or fifo hardware.
 265  */
 266
 267 static int spi_bitbang_prepare_hardware(struct spi_master *spi)
 268 {
 269         struct spi_bitbang      *bitbang;
 270
 271         bitbang = spi_master_get_devdata(spi);
 272
 273         mutex_lock(&bitbang->lock);
 274         bitbang->busy = 1;
 275         mutex_unlock(&bitbang->lock);
 276
 277         return 0;
 278 }
 279
 280 static int spi_bitbang_transfer_one(struct spi_master *master,
 281                                     struct spi_device *spi,
 282                                     struct spi_transfer *transfer)
 283 {
 284         struct spi_bitbang *bitbang = spi_master_get_devdata(master);
 285         int status = 0;
 286
 287         if (bitbang->setup_transfer) {
 288                 status = bitbang->setup_transfer(spi, transfer);
 289                 if (status < 0)
 290                         goto out;
 291         }
 292
 293         if (transfer->len)
 294                 status = bitbang->txrx_bufs(spi, transfer);
 295
 296         if (status == transfer->len)
 297                 status = 0;
 298         else if (status >= 0)
 299                 status = -EREMOTEIO;
 300
 301 out:
 302         spi_finalize_current_transfer(master);
 303
 304         return status;
 305 }
 306
 307 static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
 308 {
 309         struct spi_bitbang      *bitbang;
 310
 311         bitbang = spi_master_get_devdata(spi);
 312
 313         mutex_lock(&bitbang->lock);
 314         bitbang->busy = 0;
 315         mutex_unlock(&bitbang->lock);
 316
 317         return 0;
 318 }
 319
 320 static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
 321 {
 322         struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master);
 323
 324         /* SPI core provides CS high / low, but bitbang driver
 325          * expects CS active
 326          * spi device driver takes care of handling SPI_CS_HIGH
 327          */
 328         enable = (!!(spi->mode & SPI_CS_HIGH) == enable);
 329
 330         ndelay(SPI_BITBANG_CS_DELAY);
 331         bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
 332                             BITBANG_CS_INACTIVE);
 333         ndelay(SPI_BITBANG_CS_DELAY);
 334 }
 335
 336 /*----------------------------------------------------------------------*/
 337
 338 /**
 339  * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 340  * @bitbang: driver handle
 341  *
 342  * Caller should have zero-initialized all parts of the structure, and then
 343  * provided callbacks for chip selection and I/O loops.  If the master has
 344  * a transfer method, its final step should call spi_bitbang_transfer; or,
 345  * that's the default if the transfer routine is not initialized.  It should
 346  * also set up the bus number and number of chipselects.
 347  *
 348  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 349  * hardware that basically exposes a shift register) or per-spi_transfer
 350  * (which takes better advantage of hardware like fifos or DMA engines).
 351  *
 352  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
 353  * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
 354  * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 355  * routine isn't initialized.
 356  *
 357  * This routine registers the spi_master, which will process requests in a
 358  * dedicated task, keeping IRQs unblocked most of the time.  To stop
 359  * processing those requests, call spi_bitbang_stop().
 360  *
 361  * On success, this routine will take a reference to master. The caller is
 362  * responsible for calling spi_bitbang_stop() to decrement the reference and
 363  * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory
 364  * leak.
 365  */
 366 int spi_bitbang_start(struct spi_bitbang *bitbang)
 367 {
 368         struct spi_master *master = bitbang->master;
 369         int ret;
 370
 371         if (!master || !bitbang->chipselect)
 372                 return -EINVAL;
 373
 374         mutex_init(&bitbang->lock);
 375
 376         if (!master->mode_bits)
 377                 master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
 378
 379         if (master->transfer || master->transfer_one_message)
 380                 return -EINVAL;
 381
 382         master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
 383         master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
 384         master->transfer_one = spi_bitbang_transfer_one;
 385         master->set_cs = spi_bitbang_set_cs;
 386
 387         if (!bitbang->txrx_bufs) {
 388                 bitbang->use_dma = 0;
 389                 bitbang->txrx_bufs = spi_bitbang_bufs;
 390                 if (!master->setup) {
 391                         if (!bitbang->setup_transfer)
 392                                 bitbang->setup_transfer =
 393                                          spi_bitbang_setup_transfer;
 394                         master->setup = spi_bitbang_setup;
 395                         master->cleanup = spi_bitbang_cleanup;
 396                 }
 397         }
 398
 399         /* driver may get busy before register() returns, especially
 400          * if someone registered boardinfo for devices
 401          */
 402         ret = spi_register_master(spi_master_get(master));
 403         if (ret)
 404                 spi_master_put(master);
 405
 406         return 0;
 407 }
 408 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 409
 410 /**
 411  * spi_bitbang_stop - stops the task providing spi communication
 412  */
 413 void spi_bitbang_stop(struct spi_bitbang *bitbang)
 414 {
 415         spi_unregister_master(bitbang->master);
 416 }
 417 EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 418
 419 MODULE_LICENSE("GPL");
 420