drivers/spi/spi_bitbang.c

   1 /*
   2  * spi_bitbang.c - 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/config.h>
  20 #include <linux/init.h>
  21 #include <linux/spinlock.h>
  22 #include <linux/workqueue.h>
  23 #include <linux/interrupt.h>
  24 #include <linux/delay.h>
  25 #include <linux/errno.h>
  26 #include <linux/platform_device.h>
  27
  28 #include <linux/spi/spi.h>
  29 #include <linux/spi/spi_bitbang.h>
  30
  31
  32 /*----------------------------------------------------------------------*/
  33
  34 /*
  35  * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
  36  * Use this for GPIO or shift-register level hardware APIs.
  37  *
  38  * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
  39  * to glue code.  These bitbang setup() and cleanup() routines are always
  40  * used, though maybe they're called from controller-aware code.
  41  *
  42  * chipselect() and friends may use use spi_device->controller_data and
  43  * controller registers as appropriate.
  44  *
  45  *
  46  * NOTE:  SPI controller pins can often be used as GPIO pins instead,
  47  * which means you could use a bitbang driver either to get hardware
  48  * working quickly, or testing for differences that aren't speed related.
  49  */
  50
  51 struct spi_bitbang_cs {
  52         unsigned        nsecs;  /* (clock cycle time)/2 */
  53         u32             (*txrx_word)(struct spi_device *spi, unsigned nsecs,
  54                                         u32 word, u8 bits);
  55         unsigned        (*txrx_bufs)(struct spi_device *,
  56                                         u32 (*txrx_word)(
  57                                                 struct spi_device *spi,
  58                                                 unsigned nsecs,
  59                                                 u32 word, u8 bits),
  60                                         unsigned, struct spi_transfer *);
  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                ns,
  69         struct spi_transfer     *t
  70 ) {
  71         unsigned                bits = spi->bits_per_word;
  72         unsigned                count = t->len;
  73         const u8                *tx = t->tx_buf;
  74         u8                      *rx = t->rx_buf;
  75
  76         while (likely(count > 0)) {
  77                 u8              word = 0;
  78
  79                 if (tx)
  80                         word = *tx++;
  81                 word = txrx_word(spi, ns, word, bits);
  82                 if (rx)
  83                         *rx++ = word;
  84                 count -= 1;
  85         }
  86         return t->len - count;
  87 }
  88
  89 static unsigned bitbang_txrx_16(
  90         struct spi_device       *spi,
  91         u32                     (*txrx_word)(struct spi_device *spi,
  92                                         unsigned nsecs,
  93                                         u32 word, u8 bits),
  94         unsigned                ns,
  95         struct spi_transfer     *t
  96 ) {
  97         unsigned                bits = spi->bits_per_word;
  98         unsigned                count = t->len;
  99         const u16               *tx = t->tx_buf;
 100         u16                     *rx = t->rx_buf;
 101
 102         while (likely(count > 1)) {
 103                 u16             word = 0;
 104
 105                 if (tx)
 106                         word = *tx++;
 107                 word = txrx_word(spi, ns, word, bits);
 108                 if (rx)
 109                         *rx++ = word;
 110                 count -= 2;
 111         }
 112         return t->len - count;
 113 }
 114
 115 static unsigned bitbang_txrx_32(
 116         struct spi_device       *spi,
 117         u32                     (*txrx_word)(struct spi_device *spi,
 118                                         unsigned nsecs,
 119                                         u32 word, u8 bits),
 120         unsigned                ns,
 121         struct spi_transfer     *t
 122 ) {
 123         unsigned                bits = spi->bits_per_word;
 124         unsigned                count = t->len;
 125         const u32               *tx = t->tx_buf;
 126         u32                     *rx = t->rx_buf;
 127
 128         while (likely(count > 3)) {
 129                 u32             word = 0;
 130
 131                 if (tx)
 132                         word = *tx++;
 133                 word = txrx_word(spi, ns, word, bits);
 134                 if (rx)
 135                         *rx++ = word;
 136                 count -= 4;
 137         }
 138         return t->len - count;
 139 }
 140
 141 /**
 142  * spi_bitbang_setup - default setup for per-word I/O loops
 143  */
 144 int spi_bitbang_setup(struct spi_device *spi)
 145 {
 146         struct spi_bitbang_cs   *cs = spi->controller_state;
 147         struct spi_bitbang      *bitbang;
 148
 149         if (!spi->max_speed_hz)
 150                 return -EINVAL;
 151
 152         if (!cs) {
 153                 cs = kzalloc(sizeof *cs, SLAB_KERNEL);
 154                 if (!cs)
 155                         return -ENOMEM;
 156                 spi->controller_state = cs;
 157         }
 158         bitbang = spi_master_get_devdata(spi->master);
 159
 160         if (!spi->bits_per_word)
 161                 spi->bits_per_word = 8;
 162
 163         /* spi_transfer level calls that work per-word */
 164         if (spi->bits_per_word <= 8)
 165                 cs->txrx_bufs = bitbang_txrx_8;
 166         else if (spi->bits_per_word <= 16)
 167                 cs->txrx_bufs = bitbang_txrx_16;
 168         else if (spi->bits_per_word <= 32)
 169                 cs->txrx_bufs = bitbang_txrx_32;
 170         else
 171                 return -EINVAL;
 172
 173         /* per-word shift register access, in hardware or bitbanging */
 174         cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 175         if (!cs->txrx_word)
 176                 return -EINVAL;
 177
 178         /* nsecs = (clock period)/2 */
 179         cs->nsecs = (1000000000/2) / (spi->max_speed_hz);
 180         if (cs->nsecs > MAX_UDELAY_MS * 1000)
 181                 return -EINVAL;
 182
 183         dev_dbg(&spi->dev, "%s, mode %d, %u bits/w, %u nsec\n",
 184                         __FUNCTION__, spi->mode & (SPI_CPOL | SPI_CPHA),
 185                         spi->bits_per_word, 2 * cs->nsecs);
 186
 187         /* NOTE we _need_ to call chipselect() early, ideally with adapter
 188          * setup, unless the hardware defaults cooperate to avoid confusion
 189          * between normal (active low) and inverted chipselects.
 190          */
 191
 192         /* deselect chip (low or high) */
 193         spin_lock(&bitbang->lock);
 194         if (!bitbang->busy) {
 195                 bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 196                 ndelay(cs->nsecs);
 197         }
 198         spin_unlock(&bitbang->lock);
 199
 200         return 0;
 201 }
 202 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 203
 204 /**
 205  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 206  */
 207 void spi_bitbang_cleanup(const struct spi_device *spi)
 208 {
 209         kfree(spi->controller_state);
 210 }
 211 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 212
 213 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 214 {
 215         struct spi_bitbang_cs   *cs = spi->controller_state;
 216         unsigned                nsecs = cs->nsecs;
 217
 218         return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t);
 219 }
 220
 221 /*----------------------------------------------------------------------*/
 222
 223 /*
 224  * SECOND PART ... simple transfer queue runner.
 225  *
 226  * This costs a task context per controller, running the queue by
 227  * performing each transfer in sequence.  Smarter hardware can queue
 228  * several DMA transfers at once, and process several controller queues
 229  * in parallel; this driver doesn't match such hardware very well.
 230  *
 231  * Drivers can provide word-at-a-time i/o primitives, or provide
 232  * transfer-at-a-time ones to leverage dma or fifo hardware.
 233  */
 234 static void bitbang_work(void *_bitbang)
 235 {
 236         struct spi_bitbang      *bitbang = _bitbang;
 237         unsigned long           flags;
 238
 239         spin_lock_irqsave(&bitbang->lock, flags);
 240         bitbang->busy = 1;
 241         while (!list_empty(&bitbang->queue)) {
 242                 struct spi_message      *m;
 243                 struct spi_device       *spi;
 244                 unsigned                nsecs;
 245                 struct spi_transfer     *t = NULL;
 246                 unsigned                tmp;
 247                 unsigned                cs_change;
 248                 int                     status;
 249
 250                 m = container_of(bitbang->queue.next, struct spi_message,
 251                                 queue);
 252                 list_del_init(&m->queue);
 253                 spin_unlock_irqrestore(&bitbang->lock, flags);
 254
 255                 /* FIXME this is made-up ... the correct value is known to
 256                  * word-at-a-time bitbang code, and presumably chipselect()
 257                  * should enforce these requirements too?
 258                  */
 259                 nsecs = 100;
 260
 261                 spi = m->spi;
 262                 tmp = 0;
 263                 cs_change = 1;
 264                 status = 0;
 265
 266                 list_for_each_entry (t, &m->transfers, transfer_list) {
 267                         if (bitbang->shutdown) {
 268                                 status = -ESHUTDOWN;
 269                                 break;
 270                         }
 271
 272                         /* set up default clock polarity, and activate chip;
 273                          * this implicitly updates clock and spi modes as
 274                          * previously recorded for this device via setup().
 275                          * (and also deselects any other chip that might be
 276                          * selected ...)
 277                          */
 278                         if (cs_change) {
 279                                 bitbang->chipselect(spi, BITBANG_CS_ACTIVE);
 280                                 ndelay(nsecs);
 281                         }
 282                         cs_change = t->cs_change;
 283                         if (!t->tx_buf && !t->rx_buf && t->len) {
 284                                 status = -EINVAL;
 285                                 break;
 286                         }
 287
 288                         /* transfer data.  the lower level code handles any
 289                          * new dma mappings it needs. our caller always gave
 290                          * us dma-safe buffers.
 291                          */
 292                         if (t->len) {
 293                                 /* REVISIT dma API still needs a designated
 294                                  * DMA_ADDR_INVALID; ~0 might be better.
 295                                  */
 296                                 if (!m->is_dma_mapped)
 297                                         t->rx_dma = t->tx_dma = 0;
 298                                 status = bitbang->txrx_bufs(spi, t);
 299                         }
 300                         if (status != t->len) {
 301                                 if (status > 0)
 302                                         status = -EMSGSIZE;
 303                                 break;
 304                         }
 305                         m->actual_length += status;
 306                         status = 0;
 307
 308                         /* protocol tweaks before next transfer */
 309                         if (t->delay_usecs)
 310                                 udelay(t->delay_usecs);
 311
 312                         if (!cs_change)
 313                                 continue;
 314                         if (t->transfer_list.next == &m->transfers)
 315                                 break;
 316
 317                         /* sometimes a short mid-message deselect of the chip
 318                          * may be needed to terminate a mode or command
 319                          */
 320                         ndelay(nsecs);
 321                         bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 322                         ndelay(nsecs);
 323                 }
 324
 325                 m->status = status;
 326                 m->complete(m->context);
 327
 328                 /* normally deactivate chipselect ... unless no error and
 329                  * cs_change has hinted that the next message will probably
 330                  * be for this chip too.
 331                  */
 332                 if (!(status == 0 && cs_change)) {
 333                         ndelay(nsecs);
 334                         bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 335                         ndelay(nsecs);
 336                 }
 337
 338                 spin_lock_irqsave(&bitbang->lock, flags);
 339         }
 340         bitbang->busy = 0;
 341         spin_unlock_irqrestore(&bitbang->lock, flags);
 342 }
 343
 344 /**
 345  * spi_bitbang_transfer - default submit to transfer queue
 346  */
 347 int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m)
 348 {
 349         struct spi_bitbang      *bitbang;
 350         unsigned long           flags;
 351
 352         m->actual_length = 0;
 353         m->status = -EINPROGRESS;
 354
 355         bitbang = spi_master_get_devdata(spi->master);
 356         if (bitbang->shutdown)
 357                 return -ESHUTDOWN;
 358
 359         spin_lock_irqsave(&bitbang->lock, flags);
 360         list_add_tail(&m->queue, &bitbang->queue);
 361         queue_work(bitbang->workqueue, &bitbang->work);
 362         spin_unlock_irqrestore(&bitbang->lock, flags);
 363
 364         return 0;
 365 }
 366 EXPORT_SYMBOL_GPL(spi_bitbang_transfer);
 367
 368 /*----------------------------------------------------------------------*/
 369
 370 /**
 371  * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 372  * @bitbang: driver handle
 373  *
 374  * Caller should have zero-initialized all parts of the structure, and then
 375  * provided callbacks for chip selection and I/O loops.  If the master has
 376  * a transfer method, its final step should call spi_bitbang_transfer; or,
 377  * that's the default if the transfer routine is not initialized.  It should
 378  * also set up the bus number and number of chipselects.
 379  *
 380  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 381  * hardware that basically exposes a shift register) or per-spi_transfer
 382  * (which takes better advantage of hardware like fifos or DMA engines).
 383  *
 384  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup and
 385  * spi_bitbang_cleanup to handle those spi master methods.  Those methods are
 386  * the defaults if the bitbang->txrx_bufs routine isn't initialized.
 387  *
 388  * This routine registers the spi_master, which will process requests in a
 389  * dedicated task, keeping IRQs unblocked most of the time.  To stop
 390  * processing those requests, call spi_bitbang_stop().
 391  */
 392 int spi_bitbang_start(struct spi_bitbang *bitbang)
 393 {
 394         int     status;
 395
 396         if (!bitbang->master || !bitbang->chipselect)
 397                 return -EINVAL;
 398
 399         INIT_WORK(&bitbang->work, bitbang_work, bitbang);
 400         spin_lock_init(&bitbang->lock);
 401         INIT_LIST_HEAD(&bitbang->queue);
 402
 403         if (!bitbang->master->transfer)
 404                 bitbang->master->transfer = spi_bitbang_transfer;
 405         if (!bitbang->txrx_bufs) {
 406                 bitbang->use_dma = 0;
 407                 bitbang->txrx_bufs = spi_bitbang_bufs;
 408                 if (!bitbang->master->setup) {
 409                         bitbang->master->setup = spi_bitbang_setup;
 410                         bitbang->master->cleanup = spi_bitbang_cleanup;
 411                 }
 412         } else if (!bitbang->master->setup)
 413                 return -EINVAL;
 414
 415         /* this task is the only thing to touch the SPI bits */
 416         bitbang->busy = 0;
 417         bitbang->workqueue = create_singlethread_workqueue(
 418                         bitbang->master->cdev.dev->bus_id);
 419         if (bitbang->workqueue == NULL) {
 420                 status = -EBUSY;
 421                 goto err1;
 422         }
 423
 424         /* driver may get busy before register() returns, especially
 425          * if someone registered boardinfo for devices
 426          */
 427         status = spi_register_master(bitbang->master);
 428         if (status < 0)
 429                 goto err2;
 430
 431         return status;
 432
 433 err2:
 434         destroy_workqueue(bitbang->workqueue);
 435 err1:
 436         return status;
 437 }
 438 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 439
 440 /**
 441  * spi_bitbang_stop - stops the task providing spi communication
 442  */
 443 int spi_bitbang_stop(struct spi_bitbang *bitbang)
 444 {
 445         unsigned        limit = 500;
 446
 447         spin_lock_irq(&bitbang->lock);
 448         bitbang->shutdown = 0;
 449         while (!list_empty(&bitbang->queue) && limit--) {
 450                 spin_unlock_irq(&bitbang->lock);
 451
 452                 dev_dbg(bitbang->master->cdev.dev, "wait for queue\n");
 453                 msleep(10);
 454
 455                 spin_lock_irq(&bitbang->lock);
 456         }
 457         spin_unlock_irq(&bitbang->lock);
 458         if (!list_empty(&bitbang->queue)) {
 459                 dev_err(bitbang->master->cdev.dev, "queue didn't empty\n");
 460                 return -EBUSY;
 461         }
 462
 463         destroy_workqueue(bitbang->workqueue);
 464
 465         spi_unregister_master(bitbang->master);
 466
 467         return 0;
 468 }
 469 EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 470
 471 MODULE_LICENSE("GPL");
 472