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 { 65 unsigned bits = t->bits_per_word; 66 unsigned count = t->len; 67 const u8 *tx = t->tx_buf; 68 u8 *rx = t->rx_buf; 69 70 while (likely(count > 0)) { 71 u8 word = 0; 72 73 if (tx) 74 word = *tx++; 75 word = txrx_word(spi, ns, word, bits, flags); 76 if (rx) 77 *rx++ = word; 78 count -= 1; 79 } 80 return t->len - count; 81 } 82 83 static unsigned bitbang_txrx_16( 84 struct spi_device *spi, 85 u32 (*txrx_word)(struct spi_device *spi, 86 unsigned nsecs, 87 u32 word, u8 bits, 88 unsigned flags), 89 unsigned ns, 90 struct spi_transfer *t, 91 unsigned flags 92 ) 93 { 94 unsigned bits = t->bits_per_word; 95 unsigned count = t->len; 96 const u16 *tx = t->tx_buf; 97 u16 *rx = t->rx_buf; 98 99 while (likely(count > 1)) { 100 u16 word = 0; 101 102 if (tx) 103 word = *tx++; 104 word = txrx_word(spi, ns, word, bits, flags); 105 if (rx) 106 *rx++ = word; 107 count -= 2; 108 } 109 return t->len - count; 110 } 111 112 static unsigned bitbang_txrx_32( 113 struct spi_device *spi, 114 u32 (*txrx_word)(struct spi_device *spi, 115 unsigned nsecs, 116 u32 word, u8 bits, 117 unsigned flags), 118 unsigned ns, 119 struct spi_transfer *t, 120 unsigned flags 121 ) 122 { 123 unsigned bits = t->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, flags); 134 if (rx) 135 *rx++ = word; 136 count -= 4; 137 } 138 return t->len - count; 139 } 140 141 int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t) 142 { 143 struct spi_bitbang_cs *cs = spi->controller_state; 144 u8 bits_per_word; 145 u32 hz; 146 147 if (t) { 148 bits_per_word = t->bits_per_word; 149 hz = t->speed_hz; 150 } else { 151 bits_per_word = 0; 152 hz = 0; 153 } 154 155 /* spi_transfer level calls that work per-word */ 156 if (!bits_per_word) 157 bits_per_word = spi->bits_per_word; 158 if (bits_per_word <= 8) 159 cs->txrx_bufs = bitbang_txrx_8; 160 else if (bits_per_word <= 16) 161 cs->txrx_bufs = bitbang_txrx_16; 162 else if (bits_per_word <= 32) 163 cs->txrx_bufs = bitbang_txrx_32; 164 else 165 return -EINVAL; 166 167 /* nsecs = (clock period)/2 */ 168 if (!hz) 169 hz = spi->max_speed_hz; 170 if (hz) { 171 cs->nsecs = (1000000000/2) / hz; 172 if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000)) 173 return -EINVAL; 174 } 175 176 return 0; 177 } 178 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer); 179 180 /* 181 * spi_bitbang_setup - default setup for per-word I/O loops 182 */ 183 int spi_bitbang_setup(struct spi_device *spi) 184 { 185 struct spi_bitbang_cs *cs = spi->controller_state; 186 struct spi_bitbang *bitbang; 187 bool initial_setup = false; 188 int retval; 189 190 bitbang = spi_master_get_devdata(spi->master); 191 192 if (!cs) { 193 cs = kzalloc(sizeof(*cs), GFP_KERNEL); 194 if (!cs) 195 return -ENOMEM; 196 spi->controller_state = cs; 197 initial_setup = true; 198 } 199 200 /* per-word shift register access, in hardware or bitbanging */ 201 cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)]; 202 if (!cs->txrx_word) { 203 retval = -EINVAL; 204 goto err_free; 205 } 206 207 if (bitbang->setup_transfer) { 208 retval = bitbang->setup_transfer(spi, NULL); 209 if (retval < 0) 210 goto err_free; 211 } 212 213 dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs); 214 215 return 0; 216 217 err_free: 218 if (initial_setup) 219 kfree(cs); 220 return retval; 221 } 222 EXPORT_SYMBOL_GPL(spi_bitbang_setup); 223 224 /* 225 * spi_bitbang_cleanup - default cleanup for per-word I/O loops 226 */ 227 void spi_bitbang_cleanup(struct spi_device *spi) 228 { 229 kfree(spi->controller_state); 230 } 231 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup); 232 233 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t) 234 { 235 struct spi_bitbang_cs *cs = spi->controller_state; 236 unsigned nsecs = cs->nsecs; 237 struct spi_bitbang *bitbang; 238 239 bitbang = spi_master_get_devdata(spi->master); 240 if (bitbang->set_line_direction) { 241 int err; 242 243 err = bitbang->set_line_direction(spi, !!(t->tx_buf)); 244 if (err < 0) 245 return err; 246 } 247 248 if (spi->mode & SPI_3WIRE) { 249 unsigned flags; 250 251 flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX; 252 return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags); 253 } 254 return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0); 255 } 256 257 /*----------------------------------------------------------------------*/ 258 259 /* 260 * SECOND PART ... simple transfer queue runner. 261 * 262 * This costs a task context per controller, running the queue by 263 * performing each transfer in sequence. Smarter hardware can queue 264 * several DMA transfers at once, and process several controller queues 265 * in parallel; this driver doesn't match such hardware very well. 266 * 267 * Drivers can provide word-at-a-time i/o primitives, or provide 268 * transfer-at-a-time ones to leverage dma or fifo hardware. 269 */ 270 271 static int spi_bitbang_prepare_hardware(struct spi_master *spi) 272 { 273 struct spi_bitbang *bitbang; 274 275 bitbang = spi_master_get_devdata(spi); 276 277 mutex_lock(&bitbang->lock); 278 bitbang->busy = 1; 279 mutex_unlock(&bitbang->lock); 280 281 return 0; 282 } 283 284 static int spi_bitbang_transfer_one(struct spi_master *master, 285 struct spi_device *spi, 286 struct spi_transfer *transfer) 287 { 288 struct spi_bitbang *bitbang = spi_master_get_devdata(master); 289 int status = 0; 290 291 if (bitbang->setup_transfer) { 292 status = bitbang->setup_transfer(spi, transfer); 293 if (status < 0) 294 goto out; 295 } 296 297 if (transfer->len) 298 status = bitbang->txrx_bufs(spi, transfer); 299 300 if (status == transfer->len) 301 status = 0; 302 else if (status >= 0) 303 status = -EREMOTEIO; 304 305 out: 306 spi_finalize_current_transfer(master); 307 308 return status; 309 } 310 311 static int spi_bitbang_unprepare_hardware(struct spi_master *spi) 312 { 313 struct spi_bitbang *bitbang; 314 315 bitbang = spi_master_get_devdata(spi); 316 317 mutex_lock(&bitbang->lock); 318 bitbang->busy = 0; 319 mutex_unlock(&bitbang->lock); 320 321 return 0; 322 } 323 324 static void spi_bitbang_set_cs(struct spi_device *spi, bool enable) 325 { 326 struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master); 327 328 /* SPI core provides CS high / low, but bitbang driver 329 * expects CS active 330 * spi device driver takes care of handling SPI_CS_HIGH 331 */ 332 enable = (!!(spi->mode & SPI_CS_HIGH) == enable); 333 334 ndelay(SPI_BITBANG_CS_DELAY); 335 bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE : 336 BITBANG_CS_INACTIVE); 337 ndelay(SPI_BITBANG_CS_DELAY); 338 } 339 340 /*----------------------------------------------------------------------*/ 341 342 int spi_bitbang_init(struct spi_bitbang *bitbang) 343 { 344 struct spi_master *master = bitbang->master; 345 bool custom_cs; 346 347 if (!master) 348 return -EINVAL; 349 /* 350 * We only need the chipselect callback if we are actually using it. 351 * If we just use GPIO descriptors, it is surplus. If the 352 * SPI_MASTER_GPIO_SS flag is set, we always need to call the 353 * driver-specific chipselect routine. 354 */ 355 custom_cs = (!master->use_gpio_descriptors || 356 (master->flags & SPI_MASTER_GPIO_SS)); 357 358 if (custom_cs && !bitbang->chipselect) 359 return -EINVAL; 360 361 mutex_init(&bitbang->lock); 362 363 if (!master->mode_bits) 364 master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags; 365 366 if (master->transfer || master->transfer_one_message) 367 return -EINVAL; 368 369 master->prepare_transfer_hardware = spi_bitbang_prepare_hardware; 370 master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware; 371 master->transfer_one = spi_bitbang_transfer_one; 372 /* 373 * When using GPIO descriptors, the ->set_cs() callback doesn't even 374 * get called unless SPI_MASTER_GPIO_SS is set. 375 */ 376 if (custom_cs) 377 master->set_cs = spi_bitbang_set_cs; 378 379 if (!bitbang->txrx_bufs) { 380 bitbang->use_dma = 0; 381 bitbang->txrx_bufs = spi_bitbang_bufs; 382 if (!master->setup) { 383 if (!bitbang->setup_transfer) 384 bitbang->setup_transfer = 385 spi_bitbang_setup_transfer; 386 master->setup = spi_bitbang_setup; 387 master->cleanup = spi_bitbang_cleanup; 388 } 389 } 390 391 return 0; 392 } 393 EXPORT_SYMBOL_GPL(spi_bitbang_init); 394 395 /** 396 * spi_bitbang_start - start up a polled/bitbanging SPI master driver 397 * @bitbang: driver handle 398 * 399 * Caller should have zero-initialized all parts of the structure, and then 400 * provided callbacks for chip selection and I/O loops. If the master has 401 * a transfer method, its final step should call spi_bitbang_transfer; or, 402 * that's the default if the transfer routine is not initialized. It should 403 * also set up the bus number and number of chipselects. 404 * 405 * For i/o loops, provide callbacks either per-word (for bitbanging, or for 406 * hardware that basically exposes a shift register) or per-spi_transfer 407 * (which takes better advantage of hardware like fifos or DMA engines). 408 * 409 * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup, 410 * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi 411 * master methods. Those methods are the defaults if the bitbang->txrx_bufs 412 * routine isn't initialized. 413 * 414 * This routine registers the spi_master, which will process requests in a 415 * dedicated task, keeping IRQs unblocked most of the time. To stop 416 * processing those requests, call spi_bitbang_stop(). 417 * 418 * On success, this routine will take a reference to master. The caller is 419 * responsible for calling spi_bitbang_stop() to decrement the reference and 420 * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory 421 * leak. 422 */ 423 int spi_bitbang_start(struct spi_bitbang *bitbang) 424 { 425 struct spi_master *master = bitbang->master; 426 int ret; 427 428 ret = spi_bitbang_init(bitbang); 429 if (ret) 430 return ret; 431 432 /* driver may get busy before register() returns, especially 433 * if someone registered boardinfo for devices 434 */ 435 ret = spi_register_master(spi_master_get(master)); 436 if (ret) 437 spi_master_put(master); 438 439 return ret; 440 } 441 EXPORT_SYMBOL_GPL(spi_bitbang_start); 442 443 /* 444 * spi_bitbang_stop - stops the task providing spi communication 445 */ 446 void spi_bitbang_stop(struct spi_bitbang *bitbang) 447 { 448 spi_unregister_master(bitbang->master); 449 } 450 EXPORT_SYMBOL_GPL(spi_bitbang_stop); 451 452 MODULE_LICENSE("GPL"); 453 454