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 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 spi_gpio_request(struct spi_gpio_platform_data *pdata,
 305                            const char *label, u16 *res_flags)
 306{
 307        int value;
 308
 309        /* NOTE:  SPI_*_GPIO symbols may reference "pdata" */
 310
 311        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) {
 312                value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
 313                if (value)
 314                        goto done;
 315        } else {
 316                /* HW configuration without MOSI pin */
 317                *res_flags |= SPI_MASTER_NO_TX;
 318        }
 319
 320        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) {
 321                value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
 322                if (value)
 323                        goto free_mosi;
 324        } else {
 325                /* HW configuration without MISO pin */
 326                *res_flags |= SPI_MASTER_NO_RX;
 327        }
 328
 329        value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
 330        if (value)
 331                goto free_miso;
 332
 333        goto done;
 334
 335free_miso:
 336        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
 337                gpio_free(SPI_MISO_GPIO);
 338free_mosi:
 339        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
 340                gpio_free(SPI_MOSI_GPIO);
 341done:
 342        return value;
 343}
 344
 345#ifdef CONFIG_OF
 346static struct of_device_id spi_gpio_dt_ids[] = {
 347        { .compatible = "spi-gpio" },
 348        {}
 349};
 350MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
 351
 352static int spi_gpio_probe_dt(struct platform_device *pdev)
 353{
 354        int ret;
 355        u32 tmp;
 356        struct spi_gpio_platform_data   *pdata;
 357        struct device_node *np = pdev->dev.of_node;
 358        const struct of_device_id *of_id =
 359                        of_match_device(spi_gpio_dt_ids, &pdev->dev);
 360
 361        if (!of_id)
 362                return 0;
 363
 364        pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
 365        if (!pdata)
 366                return -ENOMEM;
 367
 368        pdata->sck = of_get_named_gpio(np, "gpio-sck", 0);
 369        pdata->miso = of_get_named_gpio(np, "gpio-miso", 0);
 370        pdata->mosi = of_get_named_gpio(np, "gpio-mosi", 0);
 371
 372        ret = of_property_read_u32(np, "num-chipselects", &tmp);
 373        if (ret < 0) {
 374                dev_err(&pdev->dev, "num-chipselects property not found\n");
 375                goto error_free;
 376        }
 377
 378        pdata->num_chipselect = tmp;
 379        pdev->dev.platform_data = pdata;
 380
 381        return 1;
 382
 383error_free:
 384        devm_kfree(&pdev->dev, pdata);
 385        return ret;
 386}
 387#else
 388static inline int spi_gpio_probe_dt(struct platform_device *pdev)
 389{
 390        return 0;
 391}
 392#endif
 393
 394static int spi_gpio_probe(struct platform_device *pdev)
 395{
 396        int                             status;
 397        struct spi_master               *master;
 398        struct spi_gpio                 *spi_gpio;
 399        struct spi_gpio_platform_data   *pdata;
 400        u16 master_flags = 0;
 401        bool use_of = 0;
 402
 403        status = spi_gpio_probe_dt(pdev);
 404        if (status < 0)
 405                return status;
 406        if (status > 0)
 407                use_of = 1;
 408
 409        pdata = pdev->dev.platform_data;
 410#ifdef GENERIC_BITBANG
 411        if (!pdata || !pdata->num_chipselect)
 412                return -ENODEV;
 413#endif
 414
 415        status = spi_gpio_request(pdata, dev_name(&pdev->dev), &master_flags);
 416        if (status < 0)
 417                return status;
 418
 419        master = spi_alloc_master(&pdev->dev, sizeof(*spi_gpio) +
 420                                        (sizeof(int) * SPI_N_CHIPSEL));
 421        if (!master) {
 422                status = -ENOMEM;
 423                goto gpio_free;
 424        }
 425        spi_gpio = spi_master_get_devdata(master);
 426        platform_set_drvdata(pdev, spi_gpio);
 427
 428        spi_gpio->pdev = pdev;
 429        if (pdata)
 430                spi_gpio->pdata = *pdata;
 431
 432        master->flags = master_flags;
 433        master->bus_num = pdev->id;
 434        master->num_chipselect = SPI_N_CHIPSEL;
 435        master->setup = spi_gpio_setup;
 436        master->cleanup = spi_gpio_cleanup;
 437#ifdef CONFIG_OF
 438        master->dev.of_node = pdev->dev.of_node;
 439
 440        if (use_of) {
 441                int i;
 442                struct device_node *np = pdev->dev.of_node;
 443
 444                /*
 445                 * In DT environments, take the CS GPIO from the "cs-gpios"
 446                 * property of the node.
 447                 */
 448
 449                for (i = 0; i < SPI_N_CHIPSEL; i++)
 450                        spi_gpio->cs_gpios[i] =
 451                                of_get_named_gpio(np, "cs-gpios", i);
 452        }
 453#endif
 454
 455        spi_gpio->bitbang.master = spi_master_get(master);
 456        spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
 457
 458        if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {
 459                spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
 460                spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
 461                spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
 462                spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
 463        } else {
 464                spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
 465                spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
 466                spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
 467                spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
 468        }
 469        spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
 470        spi_gpio->bitbang.flags = SPI_CS_HIGH;
 471
 472        status = spi_bitbang_start(&spi_gpio->bitbang);
 473        if (status < 0) {
 474                spi_master_put(spi_gpio->bitbang.master);
 475gpio_free:
 476                if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
 477                        gpio_free(SPI_MISO_GPIO);
 478                if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
 479                        gpio_free(SPI_MOSI_GPIO);
 480                gpio_free(SPI_SCK_GPIO);
 481                spi_master_put(master);
 482        }
 483
 484        return status;
 485}
 486
 487static int spi_gpio_remove(struct platform_device *pdev)
 488{
 489        struct spi_gpio                 *spi_gpio;
 490        struct spi_gpio_platform_data   *pdata;
 491        int                             status;
 492
 493        spi_gpio = platform_get_drvdata(pdev);
 494        pdata = pdev->dev.platform_data;
 495
 496        /* stop() unregisters child devices too */
 497        status = spi_bitbang_stop(&spi_gpio->bitbang);
 498        spi_master_put(spi_gpio->bitbang.master);
 499
 500        platform_set_drvdata(pdev, NULL);
 501
 502        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
 503                gpio_free(SPI_MISO_GPIO);
 504        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
 505                gpio_free(SPI_MOSI_GPIO);
 506        gpio_free(SPI_SCK_GPIO);
 507
 508        return status;
 509}
 510
 511MODULE_ALIAS("platform:" DRIVER_NAME);
 512
 513static struct platform_driver spi_gpio_driver = {
 514        .driver = {
 515                .name   = DRIVER_NAME,
 516                .owner  = THIS_MODULE,
 517                .of_match_table = of_match_ptr(spi_gpio_dt_ids),
 518        },
 519        .probe          = spi_gpio_probe,
 520        .remove         = spi_gpio_remove,
 521};
 522module_platform_driver(spi_gpio_driver);
 523
 524MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
 525MODULE_AUTHOR("David Brownell");
 526MODULE_LICENSE("GPL");
 527
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