linux/drivers/spi/spi-gpio.c
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   1/*
   2 * SPI master driver using generic bitbanged GPIO
   3 *
   4 * Copyright (C) 2006,2008 David Brownell
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License as published by
   8 * the Free Software Foundation; either version 2 of the License, or
   9 * (at your option) any later version.
  10 *
  11 * This program is distributed in the hope that it will be useful,
  12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 * GNU General Public License for more details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with this program; if not, write to the Free Software
  18 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19 */
  20#include <linux/kernel.h>
  21#include <linux/module.h>
  22#include <linux/init.h>
  23#include <linux/platform_device.h>
  24#include <linux/gpio.h>
  25#include <linux/of_device.h>
  26#include <linux/of_gpio.h>
  27
  28#include <linux/spi/spi.h>
  29#include <linux/spi/spi_bitbang.h>
  30#include <linux/spi/spi_gpio.h>
  31
  32
  33/*
  34 * This bitbanging SPI master driver should help make systems usable
  35 * when a native hardware SPI engine is not available, perhaps because
  36 * its driver isn't yet working or because the I/O pins it requires
  37 * are used for other purposes.
  38 *
  39 * platform_device->driver_data ... points to spi_gpio
  40 *
  41 * spi->controller_state ... reserved for bitbang framework code
  42 * spi->controller_data ... holds chipselect GPIO
  43 *
  44 * spi->master->dev.driver_data ... points to spi_gpio->bitbang
  45 */
  46
  47struct spi_gpio {
  48        struct spi_bitbang              bitbang;
  49        struct spi_gpio_platform_data   pdata;
  50        struct platform_device          *pdev;
  51        int                             cs_gpios[0];
  52};
  53
  54/*----------------------------------------------------------------------*/
  55
  56/*
  57 * Because the overhead of going through four GPIO procedure calls
  58 * per transferred bit can make performance a problem, this code
  59 * is set up so that you can use it in either of two ways:
  60 *
  61 *   - The slow generic way:  set up platform_data to hold the GPIO
  62 *     numbers used for MISO/MOSI/SCK, and issue procedure calls for
  63 *     each of them.  This driver can handle several such busses.
  64 *
  65 *   - The quicker inlined way:  only helps with platform GPIO code
  66 *     that inlines operations for constant GPIOs.  This can give
  67 *     you tight (fast!) inner loops, but each such bus needs a
  68 *     new driver.  You'll define a new C file, with Makefile and
  69 *     Kconfig support; the C code can be a total of six lines:
  70 *
  71 *              #define DRIVER_NAME     "myboard_spi2"
  72 *              #define SPI_MISO_GPIO   119
  73 *              #define SPI_MOSI_GPIO   120
  74 *              #define SPI_SCK_GPIO    121
  75 *              #define SPI_N_CHIPSEL   4
  76 *              #include "spi-gpio.c"
  77 */
  78
  79#ifndef DRIVER_NAME
  80#define DRIVER_NAME     "spi_gpio"
  81
  82#define GENERIC_BITBANG /* vs tight inlines */
  83
  84/* all functions referencing these symbols must define pdata */
  85#define SPI_MISO_GPIO   ((pdata)->miso)
  86#define SPI_MOSI_GPIO   ((pdata)->mosi)
  87#define SPI_SCK_GPIO    ((pdata)->sck)
  88
  89#define SPI_N_CHIPSEL   ((pdata)->num_chipselect)
  90
  91#endif
  92
  93/*----------------------------------------------------------------------*/
  94
  95static inline struct spi_gpio * __pure
  96spi_to_spi_gpio(const struct spi_device *spi)
  97{
  98        const struct spi_bitbang        *bang;
  99        struct spi_gpio                 *spi_gpio;
 100
 101        bang = spi_master_get_devdata(spi->master);
 102        spi_gpio = container_of(bang, struct spi_gpio, bitbang);
 103        return spi_gpio;
 104}
 105
 106static inline struct spi_gpio_platform_data * __pure
 107spi_to_pdata(const struct spi_device *spi)
 108{
 109        return &spi_to_spi_gpio(spi)->pdata;
 110}
 111
 112/* this is #defined to avoid unused-variable warnings when inlining */
 113#define pdata           spi_to_pdata(spi)
 114
 115static inline void setsck(const struct spi_device *spi, int is_on)
 116{
 117        gpio_set_value(SPI_SCK_GPIO, is_on);
 118}
 119
 120static inline void setmosi(const struct spi_device *spi, int is_on)
 121{
 122        gpio_set_value(SPI_MOSI_GPIO, is_on);
 123}
 124
 125static inline int getmiso(const struct spi_device *spi)
 126{
 127        return !!gpio_get_value(SPI_MISO_GPIO);
 128}
 129
 130#undef pdata
 131
 132/*
 133 * NOTE:  this clocks "as fast as we can".  It "should" be a function of the
 134 * requested device clock.  Software overhead means we usually have trouble
 135 * reaching even one Mbit/sec (except when we can inline bitops), so for now
 136 * we'll just assume we never need additional per-bit slowdowns.
 137 */
 138#define spidelay(nsecs) do {} while (0)
 139
 140#include "spi-bitbang-txrx.h"
 141
 142/*
 143 * These functions can leverage inline expansion of GPIO calls to shrink
 144 * costs for a txrx bit, often by factors of around ten (by instruction
 145 * count).  That is particularly visible for larger word sizes, but helps
 146 * even with default 8-bit words.
 147 *
 148 * REVISIT overheads calling these functions for each word also have
 149 * significant performance costs.  Having txrx_bufs() calls that inline
 150 * the txrx_word() logic would help performance, e.g. on larger blocks
 151 * used with flash storage or MMC/SD.  There should also be ways to make
 152 * GCC be less stupid about reloading registers inside the I/O loops,
 153 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
 154 */
 155
 156static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
 157                unsigned nsecs, u32 word, u8 bits)
 158{
 159        return bitbang_txrx_be_cpha0(spi, nsecs, 0, 0, word, bits);
 160}
 161
 162static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
 163                unsigned nsecs, u32 word, u8 bits)
 164{
 165        return bitbang_txrx_be_cpha1(spi, nsecs, 0, 0, word, bits);
 166}
 167
 168static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
 169                unsigned nsecs, u32 word, u8 bits)
 170{
 171        return bitbang_txrx_be_cpha0(spi, nsecs, 1, 0, word, bits);
 172}
 173
 174static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
 175                unsigned nsecs, u32 word, u8 bits)
 176{
 177        return bitbang_txrx_be_cpha1(spi, nsecs, 1, 0, word, bits);
 178}
 179
 180/*
 181 * These functions do not call setmosi or getmiso if respective flag
 182 * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to
 183 * call when such pin is not present or defined in the controller.
 184 * A separate set of callbacks is defined to get highest possible
 185 * speed in the generic case (when both MISO and MOSI lines are
 186 * available), as optimiser will remove the checks when argument is
 187 * constant.
 188 */
 189
 190static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
 191                unsigned nsecs, u32 word, u8 bits)
 192{
 193        unsigned flags = spi->master->flags;
 194        return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
 195}
 196
 197static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
 198                unsigned nsecs, u32 word, u8 bits)
 199{
 200        unsigned flags = spi->master->flags;
 201        return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
 202}
 203
 204static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
 205                unsigned nsecs, u32 word, u8 bits)
 206{
 207        unsigned flags = spi->master->flags;
 208        return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
 209}
 210
 211static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
 212                unsigned nsecs, u32 word, u8 bits)
 213{
 214        unsigned flags = spi->master->flags;
 215        return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
 216}
 217
 218/*----------------------------------------------------------------------*/
 219
 220static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
 221{
 222        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 223        unsigned int cs = spi_gpio->cs_gpios[spi->chip_select];
 224
 225        /* set initial clock polarity */
 226        if (is_active)
 227                setsck(spi, spi->mode & SPI_CPOL);
 228
 229        if (cs != SPI_GPIO_NO_CHIPSELECT) {
 230                /* SPI is normally active-low */
 231                gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
 232        }
 233}
 234
 235static int spi_gpio_setup(struct spi_device *spi)
 236{
 237        unsigned int            cs;
 238        int                     status = 0;
 239        struct spi_gpio         *spi_gpio = spi_to_spi_gpio(spi);
 240        struct device_node      *np = spi->master->dev.of_node;
 241
 242        if (spi->bits_per_word > 32)
 243                return -EINVAL;
 244
 245        if (np) {
 246                /*
 247                 * In DT environments, the CS GPIOs have already been
 248                 * initialized from the "cs-gpios" property of the node.
 249                 */
 250                cs = spi_gpio->cs_gpios[spi->chip_select];
 251        } else {
 252                /*
 253                 * ... otherwise, take it from spi->controller_data
 254                 */
 255                cs = (unsigned int) spi->controller_data;
 256        }
 257
 258        if (!spi->controller_state) {
 259                if (cs != SPI_GPIO_NO_CHIPSELECT) {
 260                        status = gpio_request(cs, dev_name(&spi->dev));
 261                        if (status)
 262                                return status;
 263                        status = gpio_direction_output(cs,
 264                                        !(spi->mode & SPI_CS_HIGH));
 265                }
 266        }
 267        if (!status) {
 268                status = spi_bitbang_setup(spi);
 269                /* in case it was initialized from static board data */
 270                spi_gpio->cs_gpios[spi->chip_select] = cs;
 271        }
 272
 273        if (status) {
 274                if (!spi->controller_state && cs != SPI_GPIO_NO_CHIPSELECT)
 275                        gpio_free(cs);
 276        }
 277        return status;
 278}
 279
 280static void spi_gpio_cleanup(struct spi_device *spi)
 281{
 282        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 283        unsigned int cs = spi_gpio->cs_gpios[spi->chip_select];
 284
 285        if (cs != SPI_GPIO_NO_CHIPSELECT)
 286                gpio_free(cs);
 287        spi_bitbang_cleanup(spi);
 288}
 289
 290static int __devinit spi_gpio_alloc(unsigned pin, const char *label, bool is_in)
 291{
 292        int value;
 293
 294        value = gpio_request(pin, label);
 295        if (value == 0) {
 296                if (is_in)
 297                        value = gpio_direction_input(pin);
 298                else
 299                        value = gpio_direction_output(pin, 0);
 300        }
 301        return value;
 302}
 303
 304static int __devinit
 305spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label,
 306        u16 *res_flags)
 307{
 308        int value;
 309
 310        /* NOTE:  SPI_*_GPIO symbols may reference "pdata" */
 311
 312        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) {
 313                value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
 314                if (value)
 315                        goto done;
 316        } else {
 317                /* HW configuration without MOSI pin */
 318                *res_flags |= SPI_MASTER_NO_TX;
 319        }
 320
 321        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) {
 322                value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
 323                if (value)
 324                        goto free_mosi;
 325        } else {
 326                /* HW configuration without MISO pin */
 327                *res_flags |= SPI_MASTER_NO_RX;
 328        }
 329
 330        value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
 331        if (value)
 332                goto free_miso;
 333
 334        goto done;
 335
 336free_miso:
 337        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
 338                gpio_free(SPI_MISO_GPIO);
 339free_mosi:
 340        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
 341                gpio_free(SPI_MOSI_GPIO);
 342done:
 343        return value;
 344}
 345
 346#ifdef CONFIG_OF
 347static struct of_device_id spi_gpio_dt_ids[] = {
 348        { .compatible = "spi-gpio" },
 349        {}
 350};
 351MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
 352
 353static int spi_gpio_probe_dt(struct platform_device *pdev)
 354{
 355        int ret;
 356        u32 tmp;
 357        struct spi_gpio_platform_data   *pdata;
 358        struct device_node *np = pdev->dev.of_node;
 359        const struct of_device_id *of_id =
 360                        of_match_device(spi_gpio_dt_ids, &pdev->dev);
 361
 362        if (!of_id)
 363                return 0;
 364
 365        pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
 366        if (!pdata)
 367                return -ENOMEM;
 368
 369        pdata->sck = of_get_named_gpio(np, "gpio-sck", 0);
 370        pdata->miso = of_get_named_gpio(np, "gpio-miso", 0);
 371        pdata->mosi = of_get_named_gpio(np, "gpio-mosi", 0);
 372
 373        ret = of_property_read_u32(np, "num-chipselects", &tmp);
 374        if (ret < 0) {
 375                dev_err(&pdev->dev, "num-chipselects property not found\n");
 376                goto error_free;
 377        }
 378
 379        pdata->num_chipselect = tmp;
 380        pdev->dev.platform_data = pdata;
 381
 382        return 1;
 383
 384error_free:
 385        devm_kfree(&pdev->dev, pdata);
 386        return ret;
 387}
 388#else
 389static inline int spi_gpio_probe_dt(struct platform_device *pdev)
 390{
 391        return 0;
 392}
 393#endif
 394
 395static int __devinit spi_gpio_probe(struct platform_device *pdev)
 396{
 397        int                             status;
 398        struct spi_master               *master;
 399        struct spi_gpio                 *spi_gpio;
 400        struct spi_gpio_platform_data   *pdata;
 401        u16 master_flags = 0;
 402        bool use_of = 0;
 403
 404        status = spi_gpio_probe_dt(pdev);
 405        if (status < 0)
 406                return status;
 407        if (status > 0)
 408                use_of = 1;
 409
 410        pdata = pdev->dev.platform_data;
 411#ifdef GENERIC_BITBANG
 412        if (!pdata || !pdata->num_chipselect)
 413                return -ENODEV;
 414#endif
 415
 416        status = spi_gpio_request(pdata, dev_name(&pdev->dev), &master_flags);
 417        if (status < 0)
 418                return status;
 419
 420        master = spi_alloc_master(&pdev->dev, sizeof(*spi_gpio) +
 421                                        (sizeof(int) * SPI_N_CHIPSEL));
 422        if (!master) {
 423                status = -ENOMEM;
 424                goto gpio_free;
 425        }
 426        spi_gpio = spi_master_get_devdata(master);
 427        platform_set_drvdata(pdev, spi_gpio);
 428
 429        spi_gpio->pdev = pdev;
 430        if (pdata)
 431                spi_gpio->pdata = *pdata;
 432
 433        master->flags = master_flags;
 434        master->bus_num = pdev->id;
 435        master->num_chipselect = SPI_N_CHIPSEL;
 436        master->setup = spi_gpio_setup;
 437        master->cleanup = spi_gpio_cleanup;
 438#ifdef CONFIG_OF
 439        master->dev.of_node = pdev->dev.of_node;
 440
 441        if (use_of) {
 442                int i;
 443                struct device_node *np = pdev->dev.of_node;
 444
 445                /*
 446                 * In DT environments, take the CS GPIO from the "cs-gpios"
 447                 * property of the node.
 448                 */
 449
 450                for (i = 0; i < SPI_N_CHIPSEL; i++)
 451                        spi_gpio->cs_gpios[i] =
 452                                of_get_named_gpio(np, "cs-gpios", i);
 453        }
 454#endif
 455
 456        spi_gpio->bitbang.master = spi_master_get(master);
 457        spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
 458
 459        if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {
 460                spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
 461                spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
 462                spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
 463                spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
 464        } else {
 465                spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
 466                spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
 467                spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
 468                spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
 469        }
 470        spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
 471        spi_gpio->bitbang.flags = SPI_CS_HIGH;
 472
 473        status = spi_bitbang_start(&spi_gpio->bitbang);
 474        if (status < 0) {
 475                spi_master_put(spi_gpio->bitbang.master);
 476gpio_free:
 477                if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
 478                        gpio_free(SPI_MISO_GPIO);
 479                if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
 480                        gpio_free(SPI_MOSI_GPIO);
 481                gpio_free(SPI_SCK_GPIO);
 482                spi_master_put(master);
 483        }
 484
 485        return status;
 486}
 487
 488static int __devexit spi_gpio_remove(struct platform_device *pdev)
 489{
 490        struct spi_gpio                 *spi_gpio;
 491        struct spi_gpio_platform_data   *pdata;
 492        int                             status;
 493
 494        spi_gpio = platform_get_drvdata(pdev);
 495        pdata = pdev->dev.platform_data;
 496
 497        /* stop() unregisters child devices too */
 498        status = spi_bitbang_stop(&spi_gpio->bitbang);
 499        spi_master_put(spi_gpio->bitbang.master);
 500
 501        platform_set_drvdata(pdev, NULL);
 502
 503        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
 504                gpio_free(SPI_MISO_GPIO);
 505        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
 506                gpio_free(SPI_MOSI_GPIO);
 507        gpio_free(SPI_SCK_GPIO);
 508
 509        return status;
 510}
 511
 512MODULE_ALIAS("platform:" DRIVER_NAME);
 513
 514static struct platform_driver spi_gpio_driver = {
 515        .driver = {
 516                .name   = DRIVER_NAME,
 517                .owner  = THIS_MODULE,
 518                .of_match_table = of_match_ptr(spi_gpio_dt_ids),
 519        },
 520        .probe          = spi_gpio_probe,
 521        .remove         = __devexit_p(spi_gpio_remove),
 522};
 523module_platform_driver(spi_gpio_driver);
 524
 525MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
 526MODULE_AUTHOR("David Brownell");
 527MODULE_LICENSE("GPL");
 528
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