spi-gpio.c

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/*
 * SPI master driver using generic bitbanged GPIO
 *
 * Copyright (C) 2006,2008 David Brownell
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/gpio.h>
#include <linux/of_device.h>
#include <linux/of_gpio.h>

#include <linux/spi/spi.h>
#include <linux/spi/spi_bitbang.h>
#include <linux/spi/spi_gpio.h>


/*
 * This bitbanging SPI master driver should help make systems usable
 * when a native hardware SPI engine is not available, perhaps because
 * its driver isn't yet working or because the I/O pins it requires
 * are used for other purposes.
 *
 * platform_device->driver_data ... points to spi_gpio
 *
 * spi->controller_state ... reserved for bitbang framework code
 * spi->controller_data ... holds chipselect GPIO
 *
 * spi->master->dev.driver_data ... points to spi_gpio->bitbang
 */

struct spi_gpio {
    struct spi_bitbang      bitbang;
    struct spi_gpio_platform_data   pdata;
    struct platform_device      *pdev;
    int             cs_gpios[0];
};

/*----------------------------------------------------------------------*/

/*
 * Because the overhead of going through four GPIO procedure calls
 * per transferred bit can make performance a problem, this code
 * is set up so that you can use it in either of two ways:
 *
 *   - The slow generic way:  set up platform_data to hold the GPIO
 *     numbers used for MISO/MOSI/SCK, and issue procedure calls for
 *     each of them.  This driver can handle several such busses.
 *
 *   - The quicker inlined way:  only helps with platform GPIO code
 *     that inlines operations for constant GPIOs.  This can give
 *     you tight (fast!) inner loops, but each such bus needs a
 *     new driver.  You'll define a new C file, with Makefile and
 *     Kconfig support; the C code can be a total of six lines:
 *
 *      #define DRIVER_NAME "myboard_spi2"
 *      #define SPI_MISO_GPIO   119
 *      #define SPI_MOSI_GPIO   120
 *      #define SPI_SCK_GPIO    121
 *      #define SPI_N_CHIPSEL   4
 *      #include "spi-gpio.c"
 */

#ifndef DRIVER_NAME
#define DRIVER_NAME "spi_gpio"

#define GENERIC_BITBANG /* vs tight inlines */

/* all functions referencing these symbols must define pdata */
#define SPI_MISO_GPIO   ((pdata)->miso)
#define SPI_MOSI_GPIO   ((pdata)->mosi)
#define SPI_SCK_GPIO    ((pdata)->sck)

#define SPI_N_CHIPSEL   ((pdata)->num_chipselect)

#endif

/*----------------------------------------------------------------------*/

static inline struct spi_gpio * __pure
spi_to_spi_gpio(const struct spi_device *spi)
{
    const struct spi_bitbang    *bang;
    struct spi_gpio         *spi_gpio;

    bang = spi_master_get_devdata(spi->master);
    spi_gpio = container_of(bang, struct spi_gpio, bitbang);
    return spi_gpio;
}

static inline struct spi_gpio_platform_data * __pure
spi_to_pdata(const struct spi_device *spi)
{
    return &spi_to_spi_gpio(spi)->pdata;
}

/* this is #defined to avoid unused-variable warnings when inlining */
#define pdata       spi_to_pdata(spi)

static inline void setsck(const struct spi_device *spi, int is_on)
{
    gpio_set_value(SPI_SCK_GPIO, is_on);
}

static inline void setmosi(const struct spi_device *spi, int is_on)
{
    gpio_set_value(SPI_MOSI_GPIO, is_on);
}

static inline int getmiso(const struct spi_device *spi)
{
    return !!gpio_get_value(SPI_MISO_GPIO);
}

#undef pdata

/*
 * NOTE:  this clocks "as fast as we can".  It "should" be a function of the
 * requested device clock.  Software overhead means we usually have trouble
 * reaching even one Mbit/sec (except when we can inline bitops), so for now
 * we'll just assume we never need additional per-bit slowdowns.
 */
#define spidelay(nsecs) do {} while (0)

#include "spi-bitbang-txrx.h"

/*
 * These functions can leverage inline expansion of GPIO calls to shrink
 * costs for a txrx bit, often by factors of around ten (by instruction
 * count).  That is particularly visible for larger word sizes, but helps
 * even with default 8-bit words.
 *
 * REVISIT overheads calling these functions for each word also have
 * significant performance costs.  Having txrx_bufs() calls that inline
 * the txrx_word() logic would help performance, e.g. on larger blocks
 * used with flash storage or MMC/SD.  There should also be ways to make
 * GCC be less stupid about reloading registers inside the I/O loops,
 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
 */

static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    return bitbang_txrx_be_cpha0(spi, nsecs, 0, 0, word, bits);
}

static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    return bitbang_txrx_be_cpha1(spi, nsecs, 0, 0, word, bits);
}

static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    return bitbang_txrx_be_cpha0(spi, nsecs, 1, 0, word, bits);
}

static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    return bitbang_txrx_be_cpha1(spi, nsecs, 1, 0, word, bits);
}

/*
 * These functions do not call setmosi or getmiso if respective flag
 * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to
 * call when such pin is not present or defined in the controller.
 * A separate set of callbacks is defined to get highest possible
 * speed in the generic case (when both MISO and MOSI lines are
 * available), as optimiser will remove the checks when argument is
 * constant.
 */

static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    unsigned flags = spi->master->flags;
    return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    unsigned flags = spi->master->flags;
    return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    unsigned flags = spi->master->flags;
    return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}

static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
        unsigned nsecs, u32 word, u8 bits)
{
    unsigned flags = spi->master->flags;
    return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
}

/*----------------------------------------------------------------------*/

static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
{
    struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
    unsigned int cs = spi_gpio->cs_gpios[spi->chip_select];

    /* set initial clock polarity */
    if (is_active)
        setsck(spi, spi->mode & SPI_CPOL);

    if (cs != SPI_GPIO_NO_CHIPSELECT) {
        /* SPI is normally active-low */
        gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
    }
}

static int spi_gpio_setup(struct spi_device *spi)
{
    unsigned int        cs;
    int         status = 0;
    struct spi_gpio     *spi_gpio = spi_to_spi_gpio(spi);
    struct device_node  *np = spi->master->dev.of_node;

    if (spi->bits_per_word > 32)
        return -EINVAL;

    if (np) {
        /*
         * In DT environments, the CS GPIOs have already been
         * initialized from the "cs-gpios" property of the node.
         */
        cs = spi_gpio->cs_gpios[spi->chip_select];
    } else {
        /*
         * ... otherwise, take it from spi->controller_data
         */
        cs = (unsigned int) spi->controller_data;
    }

    if (!spi->controller_state) {
        if (cs != SPI_GPIO_NO_CHIPSELECT) {
            status = gpio_request(cs, dev_name(&spi->dev));
            if (status)
                return status;
            status = gpio_direction_output(cs,
                    !(spi->mode & SPI_CS_HIGH));
        }
    }
    if (!status) {
        status = spi_bitbang_setup(spi);
        /* in case it was initialized from static board data */
        spi_gpio->cs_gpios[spi->chip_select] = cs;
    }

    if (status) {
        if (!spi->controller_state && cs != SPI_GPIO_NO_CHIPSELECT)
            gpio_free(cs);
    }
    return status;
}

static void spi_gpio_cleanup(struct spi_device *spi)
{
    struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
    unsigned int cs = spi_gpio->cs_gpios[spi->chip_select];

    if (cs != SPI_GPIO_NO_CHIPSELECT)
        gpio_free(cs);
    spi_bitbang_cleanup(spi);
}

static int __devinit spi_gpio_alloc(unsigned pin, const char *label, bool is_in)
{
    int value;

    value = gpio_request(pin, label);
    if (value == 0) {
        if (is_in)
            value = gpio_direction_input(pin);
        else
            value = gpio_direction_output(pin, 0);
    }
    return value;
}

static int __devinit
spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label,
    u16 *res_flags)
{
    int value;

    /* NOTE:  SPI_*_GPIO symbols may reference "pdata" */

    if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) {
        value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
        if (value)
            goto done;
    } else {
        /* HW configuration without MOSI pin */
        *res_flags |= SPI_MASTER_NO_TX;
    }

    if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) {
        value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
        if (value)
            goto free_mosi;
    } else {
        /* HW configuration without MISO pin */
        *res_flags |= SPI_MASTER_NO_RX;
    }

    value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
    if (value)
        goto free_miso;

    goto done;

free_miso:
    if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
        gpio_free(SPI_MISO_GPIO);
free_mosi:
    if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
        gpio_free(SPI_MOSI_GPIO);
done:
    return value;
}

#ifdef CONFIG_OF
static struct of_device_id spi_gpio_dt_ids[] = {
    { .compatible = "spi-gpio" },
    {}
};
MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);

static int spi_gpio_probe_dt(struct platform_device *pdev)
{
    int ret;
    u32 tmp;
    struct spi_gpio_platform_data   *pdata;
    struct device_node *np = pdev->dev.of_node;
    const struct of_device_id *of_id =
            of_match_device(spi_gpio_dt_ids, &pdev->dev);

    if (!of_id)
        return 0;

    pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
    if (!pdata)
        return -ENOMEM;

    pdata->sck = of_get_named_gpio(np, "gpio-sck", 0);
    pdata->miso = of_get_named_gpio(np, "gpio-miso", 0);
    pdata->mosi = of_get_named_gpio(np, "gpio-mosi", 0);

    ret = of_property_read_u32(np, "num-chipselects", &tmp);
    if (ret < 0) {
        dev_err(&pdev->dev, "num-chipselects property not found\n");
        goto error_free;
    }

    pdata->num_chipselect = tmp;
    pdev->dev.platform_data = pdata;

    return 1;

error_free:
    devm_kfree(&pdev->dev, pdata);
    return ret;
}
#else
static inline int spi_gpio_probe_dt(struct platform_device *pdev)
{
    return 0;
}
#endif

static int __devinit spi_gpio_probe(struct platform_device *pdev)
{
    int             status;
    struct spi_master       *master;
    struct spi_gpio         *spi_gpio;
    struct spi_gpio_platform_data   *pdata;
    u16 master_flags = 0;
    bool use_of = 0;

    status = spi_gpio_probe_dt(pdev);
    if (status < 0)
        return status;
    if (status > 0)
        use_of = 1;

    pdata = pdev->dev.platform_data;
#ifdef GENERIC_BITBANG
    if (!pdata || !pdata->num_chipselect)
        return -ENODEV;
#endif

    status = spi_gpio_request(pdata, dev_name(&pdev->dev), &master_flags);
    if (status < 0)
        return status;

    master = spi_alloc_master(&pdev->dev, sizeof(*spi_gpio) +
                    (sizeof(int) * SPI_N_CHIPSEL));
    if (!master) {
        status = -ENOMEM;
        goto gpio_free;
    }
    spi_gpio = spi_master_get_devdata(master);
    platform_set_drvdata(pdev, spi_gpio);

    spi_gpio->pdev = pdev;
    if (pdata)
        spi_gpio->pdata = *pdata;

    master->flags = master_flags;
    master->bus_num = pdev->id;
    master->num_chipselect = SPI_N_CHIPSEL;
    master->setup = spi_gpio_setup;
    master->cleanup = spi_gpio_cleanup;
#ifdef CONFIG_OF
    master->dev.of_node = pdev->dev.of_node;

    if (use_of) {
        int i;
        struct device_node *np = pdev->dev.of_node;

        /*
         * In DT environments, take the CS GPIO from the "cs-gpios"
         * property of the node.
         */

        for (i = 0; i < SPI_N_CHIPSEL; i++)
            spi_gpio->cs_gpios[i] =
                of_get_named_gpio(np, "cs-gpios", i);
    }
#endif

    spi_gpio->bitbang.master = spi_master_get(master);
    spi_gpio->bitbang.chipselect = spi_gpio_chipselect;

    if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {
        spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
        spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
        spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
        spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
    } else {
        spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
        spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
        spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
        spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
    }
    spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
    spi_gpio->bitbang.flags = SPI_CS_HIGH;

    status = spi_bitbang_start(&spi_gpio->bitbang);
    if (status < 0) {
        spi_master_put(spi_gpio->bitbang.master);
gpio_free:
        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
            gpio_free(SPI_MISO_GPIO);
        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
            gpio_free(SPI_MOSI_GPIO);
        gpio_free(SPI_SCK_GPIO);
        spi_master_put(master);
    }

    return status;
}

static int __devexit spi_gpio_remove(struct platform_device *pdev)
{
    struct spi_gpio         *spi_gpio;
    struct spi_gpio_platform_data   *pdata;
    int             status;

    spi_gpio = platform_get_drvdata(pdev);
    pdata = pdev->dev.platform_data;

    /* stop() unregisters child devices too */
    status = spi_bitbang_stop(&spi_gpio->bitbang);
    spi_master_put(spi_gpio->bitbang.master);

    platform_set_drvdata(pdev, NULL);

    if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
        gpio_free(SPI_MISO_GPIO);
    if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
        gpio_free(SPI_MOSI_GPIO);
    gpio_free(SPI_SCK_GPIO);

    return status;
}

MODULE_ALIAS("platform:" DRIVER_NAME);

static struct platform_driver spi_gpio_driver = {
    .driver = {
        .name   = DRIVER_NAME,
        .owner  = THIS_MODULE,
        .of_match_table = of_match_ptr(spi_gpio_dt_ids),
    },
    .probe      = spi_gpio_probe,
    .remove     = __devexit_p(spi_gpio_remove),
};
module_platform_driver(spi_gpio_driver);

MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
MODULE_AUTHOR("David Brownell");
MODULE_LICENSE("GPL");