root/drivers/spi/spi-gpio.c

DEFINITIONS

1. spi_to_spi_gpio
2. setsck
3. setmosi
4. getmiso
5. spi_gpio_txrx_word_mode0
6. spi_gpio_txrx_word_mode1
7. spi_gpio_txrx_word_mode2
8. spi_gpio_txrx_word_mode3
9. spi_gpio_spec_txrx_word_mode0
10. spi_gpio_spec_txrx_word_mode1
11. spi_gpio_spec_txrx_word_mode2
12. spi_gpio_spec_txrx_word_mode3
13. spi_gpio_chipselect
14. spi_gpio_setup
15. spi_gpio_set_direction
16. spi_gpio_cleanup
17. spi_gpio_request
18. spi_gpio_probe_dt
19. spi_gpio_probe_dt
20. spi_gpio_probe_pdata
21. spi_gpio_put
22. spi_gpio_probe

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * SPI master driver using generic bitbanged GPIO
   4  *
   5  * Copyright (C) 2006,2008 David Brownell
   6  * Copyright (C) 2017 Linus Walleij
   7  */
   8 #include <linux/kernel.h>
   9 #include <linux/module.h>
  10 #include <linux/platform_device.h>
  11 #include <linux/gpio/consumer.h>
  12 #include <linux/of.h>
  13 #include <linux/of_device.h>
  14 
  15 #include <linux/spi/spi.h>
  16 #include <linux/spi/spi_bitbang.h>
  17 #include <linux/spi/spi_gpio.h>
  18 
  19 
  20 /*
  21  * This bitbanging SPI master driver should help make systems usable
  22  * when a native hardware SPI engine is not available, perhaps because
  23  * its driver isn't yet working or because the I/O pins it requires
  24  * are used for other purposes.
  25  *
  26  * platform_device->driver_data ... points to spi_gpio
  27  *
  28  * spi->controller_state ... reserved for bitbang framework code
  29  *
  30  * spi->master->dev.driver_data ... points to spi_gpio->bitbang
  31  */
  32 
  33 struct spi_gpio {
  34         struct spi_bitbang              bitbang;
  35         struct gpio_desc                *sck;
  36         struct gpio_desc                *miso;
  37         struct gpio_desc                *mosi;
  38         struct gpio_desc                **cs_gpios;
  39 };
  40 
  41 /*----------------------------------------------------------------------*/
  42 
  43 /*
  44  * Because the overhead of going through four GPIO procedure calls
  45  * per transferred bit can make performance a problem, this code
  46  * is set up so that you can use it in either of two ways:
  47  *
  48  *   - The slow generic way:  set up platform_data to hold the GPIO
  49  *     numbers used for MISO/MOSI/SCK, and issue procedure calls for
  50  *     each of them.  This driver can handle several such busses.
  51  *
  52  *   - The quicker inlined way:  only helps with platform GPIO code
  53  *     that inlines operations for constant GPIOs.  This can give
  54  *     you tight (fast!) inner loops, but each such bus needs a
  55  *     new driver.  You'll define a new C file, with Makefile and
  56  *     Kconfig support; the C code can be a total of six lines:
  57  *
  58  *              #define DRIVER_NAME     "myboard_spi2"
  59  *              #define SPI_MISO_GPIO   119
  60  *              #define SPI_MOSI_GPIO   120
  61  *              #define SPI_SCK_GPIO    121
  62  *              #define SPI_N_CHIPSEL   4
  63  *              #include "spi-gpio.c"
  64  */
  65 
  66 #ifndef DRIVER_NAME
  67 #define DRIVER_NAME     "spi_gpio"
  68 
  69 #define GENERIC_BITBANG /* vs tight inlines */
  70 
  71 #endif
  72 
  73 /*----------------------------------------------------------------------*/
  74 
  75 static inline struct spi_gpio *__pure
  76 spi_to_spi_gpio(const struct spi_device *spi)
  77 {
  78         const struct spi_bitbang        *bang;
  79         struct spi_gpio                 *spi_gpio;
  80 
  81         bang = spi_master_get_devdata(spi->master);
  82         spi_gpio = container_of(bang, struct spi_gpio, bitbang);
  83         return spi_gpio;
  84 }
  85 
  86 /* These helpers are in turn called by the bitbang inlines */
  87 static inline void setsck(const struct spi_device *spi, int is_on)
  88 {
  89         struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
  90 
  91         gpiod_set_value_cansleep(spi_gpio->sck, is_on);
  92 }
  93 
  94 static inline void setmosi(const struct spi_device *spi, int is_on)
  95 {
  96         struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
  97 
  98         gpiod_set_value_cansleep(spi_gpio->mosi, is_on);
  99 }
 100 
 101 static inline int getmiso(const struct spi_device *spi)
 102 {
 103         struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 104 
 105         if (spi->mode & SPI_3WIRE)
 106                 return !!gpiod_get_value_cansleep(spi_gpio->mosi);
 107         else
 108                 return !!gpiod_get_value_cansleep(spi_gpio->miso);
 109 }
 110 
 111 /*
 112  * NOTE:  this clocks "as fast as we can".  It "should" be a function of the
 113  * requested device clock.  Software overhead means we usually have trouble
 114  * reaching even one Mbit/sec (except when we can inline bitops), so for now
 115  * we'll just assume we never need additional per-bit slowdowns.
 116  */
 117 #define spidelay(nsecs) do {} while (0)
 118 
 119 #include "spi-bitbang-txrx.h"
 120 
 121 /*
 122  * These functions can leverage inline expansion of GPIO calls to shrink
 123  * costs for a txrx bit, often by factors of around ten (by instruction
 124  * count).  That is particularly visible for larger word sizes, but helps
 125  * even with default 8-bit words.
 126  *
 127  * REVISIT overheads calling these functions for each word also have
 128  * significant performance costs.  Having txrx_bufs() calls that inline
 129  * the txrx_word() logic would help performance, e.g. on larger blocks
 130  * used with flash storage or MMC/SD.  There should also be ways to make
 131  * GCC be less stupid about reloading registers inside the I/O loops,
 132  * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
 133  */
 134 
 135 static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
 136                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 137 {
 138         return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
 139 }
 140 
 141 static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
 142                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 143 {
 144         return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
 145 }
 146 
 147 static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
 148                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 149 {
 150         return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
 151 }
 152 
 153 static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
 154                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 155 {
 156         return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
 157 }
 158 
 159 /*
 160  * These functions do not call setmosi or getmiso if respective flag
 161  * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to
 162  * call when such pin is not present or defined in the controller.
 163  * A separate set of callbacks is defined to get highest possible
 164  * speed in the generic case (when both MISO and MOSI lines are
 165  * available), as optimiser will remove the checks when argument is
 166  * constant.
 167  */
 168 
 169 static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
 170                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 171 {
 172         flags = spi->master->flags;
 173         return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
 174 }
 175 
 176 static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
 177                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 178 {
 179         flags = spi->master->flags;
 180         return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
 181 }
 182 
 183 static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
 184                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 185 {
 186         flags = spi->master->flags;
 187         return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
 188 }
 189 
 190 static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
 191                 unsigned nsecs, u32 word, u8 bits, unsigned flags)
 192 {
 193         flags = spi->master->flags;
 194         return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
 195 }
 196 
 197 /*----------------------------------------------------------------------*/
 198 
 199 static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
 200 {
 201         struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 202 
 203         /* set initial clock line level */
 204         if (is_active)
 205                 gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
 206 
 207         /* Drive chip select line, if we have one */
 208         if (spi_gpio->cs_gpios) {
 209                 struct gpio_desc *cs = spi_gpio->cs_gpios[spi->chip_select];
 210 
 211                 /* SPI chip selects are normally active-low */
 212                 gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
 213         }
 214 }
 215 
 216 static int spi_gpio_setup(struct spi_device *spi)
 217 {
 218         struct gpio_desc        *cs;
 219         int                     status = 0;
 220         struct spi_gpio         *spi_gpio = spi_to_spi_gpio(spi);
 221 
 222         /*
 223          * The CS GPIOs have already been
 224          * initialized from the descriptor lookup.
 225          */
 226         if (spi_gpio->cs_gpios) {
 227                 cs = spi_gpio->cs_gpios[spi->chip_select];
 228                 if (!spi->controller_state && cs)
 229                         status = gpiod_direction_output(cs,
 230                                                   !(spi->mode & SPI_CS_HIGH));
 231         }
 232 
 233         if (!status)
 234                 status = spi_bitbang_setup(spi);
 235 
 236         return status;
 237 }
 238 
 239 static int spi_gpio_set_direction(struct spi_device *spi, bool output)
 240 {
 241         struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 242         int ret;
 243 
 244         if (output)
 245                 return gpiod_direction_output(spi_gpio->mosi, 1);
 246 
 247         ret = gpiod_direction_input(spi_gpio->mosi);
 248         if (ret)
 249                 return ret;
 250         /*
 251          * Send a turnaround high impedance cycle when switching
 252          * from output to input. Theoretically there should be
 253          * a clock delay here, but as has been noted above, the
 254          * nsec delay function for bit-banged GPIO is simply
 255          * {} because bit-banging just doesn't get fast enough
 256          * anyway.
 257          */
 258         if (spi->mode & SPI_3WIRE_HIZ) {
 259                 gpiod_set_value_cansleep(spi_gpio->sck,
 260                                          !(spi->mode & SPI_CPOL));
 261                 gpiod_set_value_cansleep(spi_gpio->sck,
 262                                          !!(spi->mode & SPI_CPOL));
 263         }
 264         return 0;
 265 }
 266 
 267 static void spi_gpio_cleanup(struct spi_device *spi)
 268 {
 269         spi_bitbang_cleanup(spi);
 270 }
 271 
 272 /*
 273  * It can be convenient to use this driver with pins that have alternate
 274  * functions associated with a "native" SPI controller if a driver for that
 275  * controller is not available, or is missing important functionality.
 276  *
 277  * On platforms which can do so, configure MISO with a weak pullup unless
 278  * there's an external pullup on that signal.  That saves power by avoiding
 279  * floating signals.  (A weak pulldown would save power too, but many
 280  * drivers expect to see all-ones data as the no slave "response".)
 281  */
 282 static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
 283 {
 284         spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW);
 285         if (IS_ERR(spi_gpio->mosi))
 286                 return PTR_ERR(spi_gpio->mosi);
 287 
 288         spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
 289         if (IS_ERR(spi_gpio->miso))
 290                 return PTR_ERR(spi_gpio->miso);
 291 
 292         spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
 293         return PTR_ERR_OR_ZERO(spi_gpio->sck);
 294 }
 295 
 296 #ifdef CONFIG_OF
 297 static const struct of_device_id spi_gpio_dt_ids[] = {
 298         { .compatible = "spi-gpio" },
 299         {}
 300 };
 301 MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
 302 
 303 static int spi_gpio_probe_dt(struct platform_device *pdev,
 304                              struct spi_master *master)
 305 {
 306         master->dev.of_node = pdev->dev.of_node;
 307         master->use_gpio_descriptors = true;
 308 
 309         return 0;
 310 }
 311 #else
 312 static inline int spi_gpio_probe_dt(struct platform_device *pdev,
 313                                     struct spi_master *master)
 314 {
 315         return 0;
 316 }
 317 #endif
 318 
 319 static int spi_gpio_probe_pdata(struct platform_device *pdev,
 320                                 struct spi_master *master)
 321 {
 322         struct device *dev = &pdev->dev;
 323         struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
 324         struct spi_gpio *spi_gpio = spi_master_get_devdata(master);
 325         int i;
 326 
 327 #ifdef GENERIC_BITBANG
 328         if (!pdata || !pdata->num_chipselect)
 329                 return -ENODEV;
 330 #endif
 331         /*
 332          * The master needs to think there is a chipselect even if not
 333          * connected
 334          */
 335         master->num_chipselect = pdata->num_chipselect ?: 1;
 336 
 337         spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect,
 338                                           sizeof(*spi_gpio->cs_gpios),
 339                                           GFP_KERNEL);
 340         if (!spi_gpio->cs_gpios)
 341                 return -ENOMEM;
 342 
 343         for (i = 0; i < master->num_chipselect; i++) {
 344                 spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
 345                                                              GPIOD_OUT_HIGH);
 346                 if (IS_ERR(spi_gpio->cs_gpios[i]))
 347                         return PTR_ERR(spi_gpio->cs_gpios[i]);
 348         }
 349 
 350         return 0;
 351 }
 352 
 353 static void spi_gpio_put(void *data)
 354 {
 355         spi_master_put(data);
 356 }
 357 
 358 static int spi_gpio_probe(struct platform_device *pdev)
 359 {
 360         int                             status;
 361         struct spi_master               *master;
 362         struct spi_gpio                 *spi_gpio;
 363         struct device                   *dev = &pdev->dev;
 364         struct spi_bitbang              *bb;
 365         const struct of_device_id       *of_id;
 366 
 367         of_id = of_match_device(spi_gpio_dt_ids, &pdev->dev);
 368 
 369         master = spi_alloc_master(dev, sizeof(*spi_gpio));
 370         if (!master)
 371                 return -ENOMEM;
 372 
 373         status = devm_add_action_or_reset(&pdev->dev, spi_gpio_put, master);
 374         if (status) {
 375                 spi_master_put(master);
 376                 return status;
 377         }
 378 
 379         if (of_id)
 380                 status = spi_gpio_probe_dt(pdev, master);
 381         else
 382                 status = spi_gpio_probe_pdata(pdev, master);
 383 
 384         if (status)
 385                 return status;
 386 
 387         spi_gpio = spi_master_get_devdata(master);
 388 
 389         status = spi_gpio_request(dev, spi_gpio);
 390         if (status)
 391                 return status;
 392 
 393         master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
 394         master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
 395                             SPI_CS_HIGH;
 396         if (!spi_gpio->mosi) {
 397                 /* HW configuration without MOSI pin
 398                  *
 399                  * No setting SPI_MASTER_NO_RX here - if there is only
 400                  * a MOSI pin connected the host can still do RX by
 401                  * changing the direction of the line.
 402                  */
 403                 master->flags = SPI_MASTER_NO_TX;
 404         }
 405 
 406         master->bus_num = pdev->id;
 407         master->setup = spi_gpio_setup;
 408         master->cleanup = spi_gpio_cleanup;
 409 
 410         bb = &spi_gpio->bitbang;
 411         bb->master = master;
 412         /*
 413          * There is some additional business, apart from driving the CS GPIO
 414          * line, that we need to do on selection. This makes the local
 415          * callback for chipselect always get called.
 416          */
 417         master->flags |= SPI_MASTER_GPIO_SS;
 418         bb->chipselect = spi_gpio_chipselect;
 419         bb->set_line_direction = spi_gpio_set_direction;
 420 
 421         if (master->flags & SPI_MASTER_NO_TX) {
 422                 bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
 423                 bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
 424                 bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
 425                 bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
 426         } else {
 427                 bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
 428                 bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
 429                 bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
 430                 bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
 431         }
 432         bb->setup_transfer = spi_bitbang_setup_transfer;
 433 
 434         status = spi_bitbang_init(&spi_gpio->bitbang);
 435         if (status)
 436                 return status;
 437 
 438         return devm_spi_register_master(&pdev->dev, spi_master_get(master));
 439 }
 440 
 441 MODULE_ALIAS("platform:" DRIVER_NAME);
 442 
 443 static struct platform_driver spi_gpio_driver = {
 444         .driver = {
 445                 .name   = DRIVER_NAME,
 446                 .of_match_table = of_match_ptr(spi_gpio_dt_ids),
 447         },
 448         .probe          = spi_gpio_probe,
 449 };
 450 module_platform_driver(spi_gpio_driver);
 451 
 452 MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
 453 MODULE_AUTHOR("David Brownell");
 454 MODULE_LICENSE("GPL");