/*

   * 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/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)

  #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)
  {
  	unsigned long cs = (unsigned long) spi->controller_data;
  
  	/* 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 long	cs = (unsigned long) spi->controller_data;
  	int		status = 0;
  
  	if (spi->bits_per_word > 32)
  		return -EINVAL;
  
  	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);
  	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)
  {
  	unsigned long	cs = (unsigned long) spi->controller_data;

  	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;
  }

  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;

  
  	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);
  	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;
  
  	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,
  	.driver.owner	= THIS_MODULE,

  	.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");