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);
  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, struct spi_transfer *);
  59 };
  60
  61 static unsigned bitbang_txrx_8(
  62         struct spi_device       *spi,
  63         u32                     (*txrx_word)(struct spi_device *spi,
  64                                         unsigned nsecs,
  65                                         u32 word, u8 bits),
  66         unsigned                ns,
  67         struct spi_transfer     *t
  68 ) {
  69         unsigned                bits = t->bits_per_word;
  70         unsigned                count = t->len;
  71         const u8                *tx = t->tx_buf;
  72         u8                      *rx = t->rx_buf;
  73
  74         while (likely(count > 0)) {
  75                 u8              word = 0;
  76
  77                 if (tx)
  78                         word = *tx++;
  79                 word = txrx_word(spi, ns, word, bits);
  80                 if (rx)
  81                         *rx++ = word;
  82                 count -= 1;
  83         }
  84         return t->len - count;
  85 }
  86
  87 static unsigned bitbang_txrx_16(
  88         struct spi_device       *spi,
  89         u32                     (*txrx_word)(struct spi_device *spi,
  90                                         unsigned nsecs,
  91                                         u32 word, u8 bits),
  92         unsigned                ns,
  93         struct spi_transfer     *t
  94 ) {
  95         unsigned                bits = t->bits_per_word;
  96         unsigned                count = t->len;
  97         const u16               *tx = t->tx_buf;
  98         u16                     *rx = t->rx_buf;
  99
 100         while (likely(count > 1)) {
 101                 u16             word = 0;
 102
 103                 if (tx)
 104                         word = *tx++;
 105                 word = txrx_word(spi, ns, word, bits);
 106                 if (rx)
 107                         *rx++ = word;
 108                 count -= 2;
 109         }
 110         return t->len - count;
 111 }
 112
 113 static unsigned bitbang_txrx_32(
 114         struct spi_device       *spi,
 115         u32                     (*txrx_word)(struct spi_device *spi,
 116                                         unsigned nsecs,
 117                                         u32 word, u8 bits),
 118         unsigned                ns,
 119         struct spi_transfer     *t
 120 ) {
 121         unsigned                bits = t->bits_per_word;
 122         unsigned                count = t->len;
 123         const u32               *tx = t->tx_buf;
 124         u32                     *rx = t->rx_buf;
 125
 126         while (likely(count > 3)) {
 127                 u32             word = 0;
 128
 129                 if (tx)
 130                         word = *tx++;
 131                 word = txrx_word(spi, ns, word, bits);
 132                 if (rx)
 133                         *rx++ = word;
 134                 count -= 4;
 135         }
 136         return t->len - count;
 137 }
 138
 139 int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 140 {
 141         struct spi_bitbang_cs   *cs = spi->controller_state;
 142         u8                      bits_per_word;
 143         u32                     hz;
 144
 145         if (t) {
 146                 bits_per_word = t->bits_per_word;
 147                 hz = t->speed_hz;
 148         } else {
 149                 bits_per_word = 0;
 150                 hz = 0;
 151         }
 152
 153         /* spi_transfer level calls that work per-word */
 154         if (!bits_per_word)
 155                 bits_per_word = spi->bits_per_word;
 156         if (bits_per_word <= 8)
 157                 cs->txrx_bufs = bitbang_txrx_8;
 158         else if (bits_per_word <= 16)
 159                 cs->txrx_bufs = bitbang_txrx_16;
 160         else if (bits_per_word <= 32)
 161                 cs->txrx_bufs = bitbang_txrx_32;
 162         else
 163                 return -EINVAL;
 164
 165         /* nsecs = (clock period)/2 */
 166         if (!hz)
 167                 hz = spi->max_speed_hz;
 168         if (hz) {
 169                 cs->nsecs = (1000000000/2) / hz;
 170                 if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
 171                         return -EINVAL;
 172         }
 173
 174         return 0;
 175 }
 176 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
 177
 178 /**
 179  * spi_bitbang_setup - default setup for per-word I/O loops
 180  */
 181 int spi_bitbang_setup(struct spi_device *spi)
 182 {
 183         struct spi_bitbang_cs   *cs = spi->controller_state;
 184         struct spi_bitbang      *bitbang;
 185
 186         bitbang = spi_master_get_devdata(spi->master);
 187
 188         if (!cs) {
 189                 cs = kzalloc(sizeof(*cs), GFP_KERNEL);
 190                 if (!cs)
 191                         return -ENOMEM;
 192                 spi->controller_state = cs;
 193         }
 194
 195         /* per-word shift register access, in hardware or bitbanging */
 196         cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 197         if (!cs->txrx_word)
 198                 return -EINVAL;
 199
 200         if (bitbang->setup_transfer) {
 201                 int retval = bitbang->setup_transfer(spi, NULL);
 202                 if (retval < 0)
 203                         return retval;
 204         }
 205
 206         dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);
 207
 208         /* NOTE we _need_ to call chipselect() early, ideally with adapter
 209          * setup, unless the hardware defaults cooperate to avoid confusion
 210          * between normal (active low) and inverted chipselects.
 211          */
 212
 213         /* deselect chip (low or high) */
 214         mutex_lock(&bitbang->lock);
 215         if (!bitbang->busy) {
 216                 bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 217                 ndelay(cs->nsecs);
 218         }
 219         mutex_unlock(&bitbang->lock);
 220
 221         return 0;
 222 }
 223 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 224
 225 /**
 226  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 227  */
 228 void spi_bitbang_cleanup(struct spi_device *spi)
 229 {
 230         kfree(spi->controller_state);
 231 }
 232 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 233
 234 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 235 {
 236         struct spi_bitbang_cs   *cs = spi->controller_state;
 237         unsigned                nsecs = cs->nsecs;
 238
 239         return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t);
 240 }
 241
 242 /*----------------------------------------------------------------------*/
 243
 244 /*
 245  * SECOND PART ... simple transfer queue runner.
 246  *
 247  * This costs a task context per controller, running the queue by
 248  * performing each transfer in sequence.  Smarter hardware can queue
 249  * several DMA transfers at once, and process several controller queues
 250  * in parallel; this driver doesn't match such hardware very well.
 251  *
 252  * Drivers can provide word-at-a-time i/o primitives, or provide
 253  * transfer-at-a-time ones to leverage dma or fifo hardware.
 254  */
 255
 256 static int spi_bitbang_prepare_hardware(struct spi_master *spi)
 257 {
 258         struct spi_bitbang      *bitbang;
 259
 260         bitbang = spi_master_get_devdata(spi);
 261
 262         mutex_lock(&bitbang->lock);
 263         bitbang->busy = 1;
 264         mutex_unlock(&bitbang->lock);
 265
 266         return 0;
 267 }
 268
 269 static int spi_bitbang_transfer_one(struct spi_master *master,
 270                                     struct spi_device *spi,
 271                                     struct spi_transfer *transfer)
 272 {
 273         struct spi_bitbang *bitbang = spi_master_get_devdata(master);
 274         int status = 0;
 275
 276         if (bitbang->setup_transfer) {
 277                 status = bitbang->setup_transfer(spi, transfer);
 278                 if (status < 0)
 279                         goto out;
 280         }
 281
 282         if (transfer->len)
 283                 status = bitbang->txrx_bufs(spi, transfer);
 284
 285         if (status == transfer->len)
 286                 status = 0;
 287         else if (status >= 0)
 288                 status = -EREMOTEIO;
 289
 290 out:
 291         spi_finalize_current_transfer(master);
 292
 293         return status;
 294 }
 295
 296 static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
 297 {
 298         struct spi_bitbang      *bitbang;
 299
 300         bitbang = spi_master_get_devdata(spi);
 301
 302         mutex_lock(&bitbang->lock);
 303         bitbang->busy = 0;
 304         mutex_unlock(&bitbang->lock);
 305
 306         return 0;
 307 }
 308
 309 static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
 310 {
 311         struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master);
 312
 313         /* SPI core provides CS high / low, but bitbang driver
 314          * expects CS active
 315          * spi device driver takes care of handling SPI_CS_HIGH
 316          */
 317         enable = (!!(spi->mode & SPI_CS_HIGH) == enable);
 318
 319         ndelay(SPI_BITBANG_CS_DELAY);
 320         bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
 321                             BITBANG_CS_INACTIVE);
 322         ndelay(SPI_BITBANG_CS_DELAY);
 323 }
 324
 325 /*----------------------------------------------------------------------*/
 326
 327 /**
 328  * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 329  * @bitbang: driver handle
 330  *
 331  * Caller should have zero-initialized all parts of the structure, and then
 332  * provided callbacks for chip selection and I/O loops.  If the master has
 333  * a transfer method, its final step should call spi_bitbang_transfer; or,
 334  * that's the default if the transfer routine is not initialized.  It should
 335  * also set up the bus number and number of chipselects.
 336  *
 337  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 338  * hardware that basically exposes a shift register) or per-spi_transfer
 339  * (which takes better advantage of hardware like fifos or DMA engines).
 340  *
 341  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
 342  * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
 343  * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 344  * routine isn't initialized.
 345  *
 346  * This routine registers the spi_master, which will process requests in a
 347  * dedicated task, keeping IRQs unblocked most of the time.  To stop
 348  * processing those requests, call spi_bitbang_stop().
 349  *
 350  * On success, this routine will take a reference to master. The caller is
 351  * responsible for calling spi_bitbang_stop() to decrement the reference and
 352  * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory
 353  * leak.
 354  */
 355 int spi_bitbang_start(struct spi_bitbang *bitbang)
 356 {
 357         struct spi_master *master = bitbang->master;
 358         int ret;
 359
 360         if (!master || !bitbang->chipselect)
 361                 return -EINVAL;
 362
 363         mutex_init(&bitbang->lock);
 364
 365         if (!master->mode_bits)
 366                 master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
 367
 368         if (master->transfer || master->transfer_one_message)
 369                 return -EINVAL;
 370
 371         master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
 372         master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
 373         master->transfer_one = spi_bitbang_transfer_one;
 374         master->set_cs = spi_bitbang_set_cs;
 375
 376         if (!bitbang->txrx_bufs) {
 377                 bitbang->use_dma = 0;
 378                 bitbang->txrx_bufs = spi_bitbang_bufs;
 379                 if (!master->setup) {
 380                         if (!bitbang->setup_transfer)
 381                                 bitbang->setup_transfer =
 382                                          spi_bitbang_setup_transfer;
 383                         master->setup = spi_bitbang_setup;
 384                         master->cleanup = spi_bitbang_cleanup;
 385                 }
 386         }
 387
 388         /* driver may get busy before register() returns, especially
 389          * if someone registered boardinfo for devices
 390          */
 391         ret = spi_register_master(spi_master_get(master));
 392         if (ret)
 393                 spi_master_put(master);
 394
 395         return 0;
 396 }
 397 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 398
 399 /**
 400  * spi_bitbang_stop - stops the task providing spi communication
 401  */
 402 void spi_bitbang_stop(struct spi_bitbang *bitbang)
 403 {
 404         spi_unregister_master(bitbang->master);
 405 }
 406 EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 407
 408 MODULE_LICENSE("GPL");
 409