drivers/spi/spi-bitbang.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * polling/bitbanging SPI master controller driver utilities
   4  */
   5
   6 #include <linux/spinlock.h>
   7 #include <linux/workqueue.h>
   8 #include <linux/interrupt.h>
   9 #include <linux/module.h>
  10 #include <linux/delay.h>
  11 #include <linux/errno.h>
  12 #include <linux/platform_device.h>
  13 #include <linux/slab.h>
  14
  15 #include <linux/spi/spi.h>
  16 #include <linux/spi/spi_bitbang.h>
  17
  18 #define SPI_BITBANG_CS_DELAY    100
  19
  20
  21 /*----------------------------------------------------------------------*/
  22
  23 /*
  24  * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
  25  * Use this for GPIO or shift-register level hardware APIs.
  26  *
  27  * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
  28  * to glue code.  These bitbang setup() and cleanup() routines are always
  29  * used, though maybe they're called from controller-aware code.
  30  *
  31  * chipselect() and friends may use spi_device->controller_data and
  32  * controller registers as appropriate.
  33  *
  34  *
  35  * NOTE:  SPI controller pins can often be used as GPIO pins instead,
  36  * which means you could use a bitbang driver either to get hardware
  37  * working quickly, or testing for differences that aren't speed related.
  38  */
  39
  40 struct spi_bitbang_cs {
  41         unsigned        nsecs;  /* (clock cycle time)/2 */
  42         u32             (*txrx_word)(struct spi_device *spi, unsigned nsecs,
  43                                         u32 word, u8 bits, unsigned flags);
  44         unsigned        (*txrx_bufs)(struct spi_device *,
  45                                         u32 (*txrx_word)(
  46                                                 struct spi_device *spi,
  47                                                 unsigned nsecs,
  48                                                 u32 word, u8 bits,
  49                                                 unsigned flags),
  50                                         unsigned, struct spi_transfer *,
  51                                         unsigned);
  52 };
  53
  54 static unsigned bitbang_txrx_8(
  55         struct spi_device       *spi,
  56         u32                     (*txrx_word)(struct spi_device *spi,
  57                                         unsigned nsecs,
  58                                         u32 word, u8 bits,
  59                                         unsigned flags),
  60         unsigned                ns,
  61         struct spi_transfer     *t,
  62         unsigned flags
  63 ) {
  64         unsigned                bits = t->bits_per_word;
  65         unsigned                count = t->len;
  66         const u8                *tx = t->tx_buf;
  67         u8                      *rx = t->rx_buf;
  68
  69         while (likely(count > 0)) {
  70                 u8              word = 0;
  71
  72                 if (tx)
  73                         word = *tx++;
  74                 word = txrx_word(spi, ns, word, bits, flags);
  75                 if (rx)
  76                         *rx++ = word;
  77                 count -= 1;
  78         }
  79         return t->len - count;
  80 }
  81
  82 static unsigned bitbang_txrx_16(
  83         struct spi_device       *spi,
  84         u32                     (*txrx_word)(struct spi_device *spi,
  85                                         unsigned nsecs,
  86                                         u32 word, u8 bits,
  87                                         unsigned flags),
  88         unsigned                ns,
  89         struct spi_transfer     *t,
  90         unsigned flags
  91 ) {
  92         unsigned                bits = t->bits_per_word;
  93         unsigned                count = t->len;
  94         const u16               *tx = t->tx_buf;
  95         u16                     *rx = t->rx_buf;
  96
  97         while (likely(count > 1)) {
  98                 u16             word = 0;
  99
 100                 if (tx)
 101                         word = *tx++;
 102                 word = txrx_word(spi, ns, word, bits, flags);
 103                 if (rx)
 104                         *rx++ = word;
 105                 count -= 2;
 106         }
 107         return t->len - count;
 108 }
 109
 110 static unsigned bitbang_txrx_32(
 111         struct spi_device       *spi,
 112         u32                     (*txrx_word)(struct spi_device *spi,
 113                                         unsigned nsecs,
 114                                         u32 word, u8 bits,
 115                                         unsigned flags),
 116         unsigned                ns,
 117         struct spi_transfer     *t,
 118         unsigned flags
 119 ) {
 120         unsigned                bits = t->bits_per_word;
 121         unsigned                count = t->len;
 122         const u32               *tx = t->tx_buf;
 123         u32                     *rx = t->rx_buf;
 124
 125         while (likely(count > 3)) {
 126                 u32             word = 0;
 127
 128                 if (tx)
 129                         word = *tx++;
 130                 word = txrx_word(spi, ns, word, bits, flags);
 131                 if (rx)
 132                         *rx++ = word;
 133                 count -= 4;
 134         }
 135         return t->len - count;
 136 }
 137
 138 int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 139 {
 140         struct spi_bitbang_cs   *cs = spi->controller_state;
 141         u8                      bits_per_word;
 142         u32                     hz;
 143
 144         if (t) {
 145                 bits_per_word = t->bits_per_word;
 146                 hz = t->speed_hz;
 147         } else {
 148                 bits_per_word = 0;
 149                 hz = 0;
 150         }
 151
 152         /* spi_transfer level calls that work per-word */
 153         if (!bits_per_word)
 154                 bits_per_word = spi->bits_per_word;
 155         if (bits_per_word <= 8)
 156                 cs->txrx_bufs = bitbang_txrx_8;
 157         else if (bits_per_word <= 16)
 158                 cs->txrx_bufs = bitbang_txrx_16;
 159         else if (bits_per_word <= 32)
 160                 cs->txrx_bufs = bitbang_txrx_32;
 161         else
 162                 return -EINVAL;
 163
 164         /* nsecs = (clock period)/2 */
 165         if (!hz)
 166                 hz = spi->max_speed_hz;
 167         if (hz) {
 168                 cs->nsecs = (1000000000/2) / hz;
 169                 if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
 170                         return -EINVAL;
 171         }
 172
 173         return 0;
 174 }
 175 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
 176
 177 /*
 178  * spi_bitbang_setup - default setup for per-word I/O loops
 179  */
 180 int spi_bitbang_setup(struct spi_device *spi)
 181 {
 182         struct spi_bitbang_cs   *cs = spi->controller_state;
 183         struct spi_bitbang      *bitbang;
 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         return 0;
 208 }
 209 EXPORT_SYMBOL_GPL(spi_bitbang_setup);
 210
 211 /*
 212  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
 213  */
 214 void spi_bitbang_cleanup(struct spi_device *spi)
 215 {
 216         kfree(spi->controller_state);
 217 }
 218 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
 219
 220 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 221 {
 222         struct spi_bitbang_cs   *cs = spi->controller_state;
 223         unsigned                nsecs = cs->nsecs;
 224         struct spi_bitbang      *bitbang;
 225
 226         bitbang = spi_master_get_devdata(spi->master);
 227         if (bitbang->set_line_direction) {
 228                 int err;
 229
 230                 err = bitbang->set_line_direction(spi, !!(t->tx_buf));
 231                 if (err < 0)
 232                         return err;
 233         }
 234
 235         if (spi->mode & SPI_3WIRE) {
 236                 unsigned flags;
 237
 238                 flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX;
 239                 return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
 240         }
 241         return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
 242 }
 243
 244 /*----------------------------------------------------------------------*/
 245
 246 /*
 247  * SECOND PART ... simple transfer queue runner.
 248  *
 249  * This costs a task context per controller, running the queue by
 250  * performing each transfer in sequence.  Smarter hardware can queue
 251  * several DMA transfers at once, and process several controller queues
 252  * in parallel; this driver doesn't match such hardware very well.
 253  *
 254  * Drivers can provide word-at-a-time i/o primitives, or provide
 255  * transfer-at-a-time ones to leverage dma or fifo hardware.
 256  */
 257
 258 static int spi_bitbang_prepare_hardware(struct spi_master *spi)
 259 {
 260         struct spi_bitbang      *bitbang;
 261
 262         bitbang = spi_master_get_devdata(spi);
 263
 264         mutex_lock(&bitbang->lock);
 265         bitbang->busy = 1;
 266         mutex_unlock(&bitbang->lock);
 267
 268         return 0;
 269 }
 270
 271 static int spi_bitbang_transfer_one(struct spi_master *master,
 272                                     struct spi_device *spi,
 273                                     struct spi_transfer *transfer)
 274 {
 275         struct spi_bitbang *bitbang = spi_master_get_devdata(master);
 276         int status = 0;
 277
 278         if (bitbang->setup_transfer) {
 279                 status = bitbang->setup_transfer(spi, transfer);
 280                 if (status < 0)
 281                         goto out;
 282         }
 283
 284         if (transfer->len)
 285                 status = bitbang->txrx_bufs(spi, transfer);
 286
 287         if (status == transfer->len)
 288                 status = 0;
 289         else if (status >= 0)
 290                 status = -EREMOTEIO;
 291
 292 out:
 293         spi_finalize_current_transfer(master);
 294
 295         return status;
 296 }
 297
 298 static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
 299 {
 300         struct spi_bitbang      *bitbang;
 301
 302         bitbang = spi_master_get_devdata(spi);
 303
 304         mutex_lock(&bitbang->lock);
 305         bitbang->busy = 0;
 306         mutex_unlock(&bitbang->lock);
 307
 308         return 0;
 309 }
 310
 311 static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
 312 {
 313         struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master);
 314
 315         /* SPI core provides CS high / low, but bitbang driver
 316          * expects CS active
 317          * spi device driver takes care of handling SPI_CS_HIGH
 318          */
 319         enable = (!!(spi->mode & SPI_CS_HIGH) == enable);
 320
 321         ndelay(SPI_BITBANG_CS_DELAY);
 322         bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
 323                             BITBANG_CS_INACTIVE);
 324         ndelay(SPI_BITBANG_CS_DELAY);
 325 }
 326
 327 /*----------------------------------------------------------------------*/
 328
 329 int spi_bitbang_init(struct spi_bitbang *bitbang)
 330 {
 331         struct spi_master *master = bitbang->master;
 332         bool custom_cs;
 333
 334         if (!master)
 335                 return -EINVAL;
 336         /*
 337          * We only need the chipselect callback if we are actually using it.
 338          * If we just use GPIO descriptors, it is surplus. If the
 339          * SPI_MASTER_GPIO_SS flag is set, we always need to call the
 340          * driver-specific chipselect routine.
 341          */
 342         custom_cs = (!master->use_gpio_descriptors ||
 343                      (master->flags & SPI_MASTER_GPIO_SS));
 344
 345         if (custom_cs && !bitbang->chipselect)
 346                 return -EINVAL;
 347
 348         mutex_init(&bitbang->lock);
 349
 350         if (!master->mode_bits)
 351                 master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
 352
 353         if (master->transfer || master->transfer_one_message)
 354                 return -EINVAL;
 355
 356         master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
 357         master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
 358         master->transfer_one = spi_bitbang_transfer_one;
 359         /*
 360          * When using GPIO descriptors, the ->set_cs() callback doesn't even
 361          * get called unless SPI_MASTER_GPIO_SS is set.
 362          */
 363         if (custom_cs)
 364                 master->set_cs = spi_bitbang_set_cs;
 365
 366         if (!bitbang->txrx_bufs) {
 367                 bitbang->use_dma = 0;
 368                 bitbang->txrx_bufs = spi_bitbang_bufs;
 369                 if (!master->setup) {
 370                         if (!bitbang->setup_transfer)
 371                                 bitbang->setup_transfer =
 372                                          spi_bitbang_setup_transfer;
 373                         master->setup = spi_bitbang_setup;
 374                         master->cleanup = spi_bitbang_cleanup;
 375                 }
 376         }
 377
 378         return 0;
 379 }
 380 EXPORT_SYMBOL_GPL(spi_bitbang_init);
 381
 382 /**
 383  * spi_bitbang_start - start up a polled/bitbanging SPI master driver
 384  * @bitbang: driver handle
 385  *
 386  * Caller should have zero-initialized all parts of the structure, and then
 387  * provided callbacks for chip selection and I/O loops.  If the master has
 388  * a transfer method, its final step should call spi_bitbang_transfer; or,
 389  * that's the default if the transfer routine is not initialized.  It should
 390  * also set up the bus number and number of chipselects.
 391  *
 392  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
 393  * hardware that basically exposes a shift register) or per-spi_transfer
 394  * (which takes better advantage of hardware like fifos or DMA engines).
 395  *
 396  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
 397  * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
 398  * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 399  * routine isn't initialized.
 400  *
 401  * This routine registers the spi_master, which will process requests in a
 402  * dedicated task, keeping IRQs unblocked most of the time.  To stop
 403  * processing those requests, call spi_bitbang_stop().
 404  *
 405  * On success, this routine will take a reference to master. The caller is
 406  * responsible for calling spi_bitbang_stop() to decrement the reference and
 407  * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory
 408  * leak.
 409  */
 410 int spi_bitbang_start(struct spi_bitbang *bitbang)
 411 {
 412         struct spi_master *master = bitbang->master;
 413         int ret;
 414
 415         ret = spi_bitbang_init(bitbang);
 416         if (ret)
 417                 return ret;
 418
 419         /* driver may get busy before register() returns, especially
 420          * if someone registered boardinfo for devices
 421          */
 422         ret = spi_register_master(spi_master_get(master));
 423         if (ret)
 424                 spi_master_put(master);
 425
 426         return ret;
 427 }
 428 EXPORT_SYMBOL_GPL(spi_bitbang_start);
 429
 430 /*
 431  * spi_bitbang_stop - stops the task providing spi communication
 432  */
 433 void spi_bitbang_stop(struct spi_bitbang *bitbang)
 434 {
 435         spi_unregister_master(bitbang->master);
 436 }
 437 EXPORT_SYMBOL_GPL(spi_bitbang_stop);
 438
 439 MODULE_LICENSE("GPL");
 440