drivers/spi/spi_gpio.c

/*
 * spi_gpio.c - 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/init.h>
#include <linux/platform_device.h>
#include <linux/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;
};

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

/*
 * 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 const struct spi_gpio_platform_data * __pure
spi_to_pdata(const struct spi_device *spi)
{
	const struct spi_bitbang	*bang;
	const struct spi_gpio		*spi_gpio;

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

#define	EXPAND_BITBANG_TXRX
#include <linux/spi/spi_bitbang.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, 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, 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, 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, word, bits);
}

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

static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
{
	unsigned long cs = (unsigned long) spi->controller_data;

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

	/* 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 long	cs = (unsigned long) spi->controller_data;
	int		status = 0;

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

	if (!spi->controller_state) {
		status = gpio_request(cs, spi->dev.bus_id);
		if (status)
			return status;
		status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH);
	}
	if (!status)
		status = spi_bitbang_setup(spi);
	if (status) {
		if (!spi->controller_state)
			gpio_free(cs);
	}
	return status;
}

static void spi_gpio_cleanup(struct spi_device *spi)
{
	unsigned long	cs = (unsigned long) spi->controller_data;

	gpio_free(cs);
	spi_bitbang_cleanup(spi);
}

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

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

	value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
	if (value)
		goto done;

	value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
	if (value)
		goto free_mosi;

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

	goto done;

free_miso:
	gpio_free(SPI_MISO_GPIO);
free_mosi:
	gpio_free(SPI_MOSI_GPIO);
done:
	return value;
}

static int __init spi_gpio_probe(struct platform_device *pdev)
{
	int				status;
	struct spi_master		*master;
	struct spi_gpio			*spi_gpio;
	struct spi_gpio_platform_data	*pdata;

	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));
	if (status < 0)
		return status;

	master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio);
	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->bus_num = pdev->id;
	master->num_chipselect = SPI_N_CHIPSEL;
	master->setup = spi_gpio_setup;
	master->cleanup = spi_gpio_cleanup;

	spi_gpio->bitbang.master = spi_master_get(master);
	spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
	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;
	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:
		gpio_free(SPI_MISO_GPIO);
		gpio_free(SPI_MOSI_GPIO);
		gpio_free(SPI_SCK_GPIO);
		spi_master_put(master);
	}

	return status;
}

static int __exit 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);

	gpio_free(SPI_MISO_GPIO);
	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,
	.driver.owner	= THIS_MODULE,
	.remove		= __exit_p(spi_gpio_remove),
};

static int __init spi_gpio_init(void)
{
	return platform_driver_probe(&spi_gpio_driver, spi_gpio_probe);
}
module_init(spi_gpio_init);

static void __exit spi_gpio_exit(void)
{
	platform_driver_unregister(&spi_gpio_driver);
}
module_exit(spi_gpio_exit);


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