drivers/spi/spi-bitbang.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Polling/bitbanging SPI host controller controller driver utilities
  */

 #include <linux/spinlock.h>
 #include <linux/workqueue.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/delay.h>
 #include <linux/errno.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 #include <linux/time64.h>

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

 #define SPI_BITBANG_CS_DELAY	100


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

 /*
  * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
  * Use this for GPIO or shift-register level hardware APIs.
  *
  * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
  * to glue code.  These bitbang setup() and cleanup() routines are always
  * used, though maybe they're called from controller-aware code.
  *
  * chipselect() and friends may use spi_device->controller_data and
  * controller registers as appropriate.
  *
  *
  * NOTE:  SPI controller pins can often be used as GPIO pins instead,
  * which means you could use a bitbang driver either to get hardware
  * working quickly, or testing for differences that aren't speed related.
  */

 typedef unsigned int (*spi_bb_txrx_bufs_fn)(struct spi_device *, spi_bb_txrx_word_fn,
 					    unsigned int, struct spi_transfer *,
 					    unsigned int);

 struct spi_bitbang_cs {
 	unsigned int nsecs;	/* (clock cycle time) / 2 */
 	spi_bb_txrx_word_fn txrx_word;
 	spi_bb_txrx_bufs_fn txrx_bufs;
 };

 static unsigned int bitbang_txrx_8(struct spi_device *spi,
 	spi_bb_txrx_word_fn txrx_word,
 	unsigned int ns,
 	struct spi_transfer	*t,
 	unsigned int flags)
 {
 	struct spi_bitbang	*bitbang;
 	unsigned int		bits = t->bits_per_word;
 	unsigned int		count = t->len;
 	const u8		*tx = t->tx_buf;
 	u8			*rx = t->rx_buf;

 	bitbang = spi_controller_get_devdata(spi->controller);
 	while (likely(count > 0)) {
 		u8		word = 0;

 		if (tx)
 			word = *tx++;
 		else
 			word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFF : 0;
 		word = txrx_word(spi, ns, word, bits, flags);
 		if (rx)
 			*rx++ = word;
 		count -= 1;
 	}
 	if (bitbang->set_mosi_idle)
 		bitbang->set_mosi_idle(spi);

 	return t->len - count;
 }

 static unsigned int bitbang_txrx_16(struct spi_device *spi,
 	spi_bb_txrx_word_fn txrx_word,
 	unsigned int ns,
 	struct spi_transfer	*t,
 	unsigned int flags)
 {
 	struct spi_bitbang	*bitbang;
 	unsigned int		bits = t->bits_per_word;
 	unsigned int		count = t->len;
 	const u16		*tx = t->tx_buf;
 	u16			*rx = t->rx_buf;

 	bitbang = spi_controller_get_devdata(spi->controller);
 	while (likely(count > 1)) {
 		u16		word = 0;

 		if (tx)
 			word = *tx++;
 		else
 			word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFFFF : 0;
 		word = txrx_word(spi, ns, word, bits, flags);
 		if (rx)
 			*rx++ = word;
 		count -= 2;
 	}
 	if (bitbang->set_mosi_idle)
 		bitbang->set_mosi_idle(spi);

 	return t->len - count;
 }

 static unsigned int bitbang_txrx_32(struct spi_device *spi,
 	spi_bb_txrx_word_fn txrx_word,
 	unsigned int ns,
 	struct spi_transfer	*t,
 	unsigned int flags)
 {
 	struct spi_bitbang	*bitbang;
 	unsigned int		bits = t->bits_per_word;
 	unsigned int		count = t->len;
 	const u32		*tx = t->tx_buf;
 	u32			*rx = t->rx_buf;

 	bitbang = spi_controller_get_devdata(spi->controller);
 	while (likely(count > 3)) {
 		u32		word = 0;

 		if (tx)
 			word = *tx++;
 		else
 			word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFFFFFFFF : 0;
 		word = txrx_word(spi, ns, word, bits, flags);
 		if (rx)
 			*rx++ = word;
 		count -= 4;
 	}
 	if (bitbang->set_mosi_idle)
 		bitbang->set_mosi_idle(spi);

 	return t->len - count;
 }

 int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	u8			bits_per_word;
 	u32			hz;

 	if (t) {
 		bits_per_word = t->bits_per_word;
 		hz = t->speed_hz;
 	} else {
 		bits_per_word = 0;
 		hz = 0;
 	}

 	/* spi_transfer level calls that work per-word */
 	if (!bits_per_word)
 		bits_per_word = spi->bits_per_word;
 	if (bits_per_word <= 8)
 		cs->txrx_bufs = bitbang_txrx_8;
 	else if (bits_per_word <= 16)
 		cs->txrx_bufs = bitbang_txrx_16;
 	else if (bits_per_word <= 32)
 		cs->txrx_bufs = bitbang_txrx_32;
 	else
 		return -EINVAL;

 	/* nsecs = (clock period)/2 */
 	if (!hz)
 		hz = spi->max_speed_hz;
 	if (hz) {
 		cs->nsecs = (NSEC_PER_SEC / 2) / hz;
 		if (cs->nsecs > (MAX_UDELAY_MS * NSEC_PER_MSEC))
 			return -EINVAL;
 	}

 	return 0;
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);

 /*
  * spi_bitbang_setup - default setup for per-word I/O loops
  */
 int spi_bitbang_setup(struct spi_device *spi)
 {
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	struct spi_bitbang	*bitbang;
 	bool			initial_setup = false;
 	int			retval;

 	bitbang = spi_controller_get_devdata(spi->controller);

 	if (!cs) {
 		cs = kzalloc(sizeof(*cs), GFP_KERNEL);
 		if (!cs)
 			return -ENOMEM;
 		spi->controller_state = cs;
 		initial_setup = true;
 	}

 	/* per-word shift register access, in hardware or bitbanging */
 	cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 	if (!cs->txrx_word) {
 		retval = -EINVAL;
 		goto err_free;
 	}

 	if (bitbang->setup_transfer) {
 		retval = bitbang->setup_transfer(spi, NULL);
 		if (retval < 0)
 			goto err_free;
 	}

 	if (bitbang->set_mosi_idle)
 		bitbang->set_mosi_idle(spi);

 	dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);

 	return 0;

 err_free:
 	if (initial_setup)
 		kfree(cs);
 	return retval;
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_setup);

 /*
  * spi_bitbang_cleanup - default cleanup for per-word I/O loops
  */
 void spi_bitbang_cleanup(struct spi_device *spi)
 {
 	kfree(spi->controller_state);
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);

 static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	unsigned int		nsecs = cs->nsecs;
 	struct spi_bitbang	*bitbang;

 	bitbang = spi_controller_get_devdata(spi->controller);
 	if (bitbang->set_line_direction) {
 		int err;

 		err = bitbang->set_line_direction(spi, !!(t->tx_buf));
 		if (err < 0)
 			return err;
 	}

 	if (spi->mode & SPI_3WIRE) {
 		unsigned int flags;

 		flags = t->tx_buf ? SPI_CONTROLLER_NO_RX : SPI_CONTROLLER_NO_TX;
 		return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
 	}
 	return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
 }

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

 /*
  * SECOND PART ... simple transfer queue runner.
  *
  * This costs a task context per controller, running the queue by
  * performing each transfer in sequence.  Smarter hardware can queue
  * several DMA transfers at once, and process several controller queues
  * in parallel; this driver doesn't match such hardware very well.
  *
  * Drivers can provide word-at-a-time i/o primitives, or provide
  * transfer-at-a-time ones to leverage dma or fifo hardware.
  */

 static int spi_bitbang_prepare_hardware(struct spi_controller *spi)
 {
 	struct spi_bitbang	*bitbang;

 	bitbang = spi_controller_get_devdata(spi);

 	mutex_lock(&bitbang->lock);
 	bitbang->busy = 1;
 	mutex_unlock(&bitbang->lock);

 	return 0;
 }

 static int spi_bitbang_transfer_one(struct spi_controller *ctlr,
 				    struct spi_device *spi,
 				    struct spi_transfer *transfer)
 {
 	struct spi_bitbang *bitbang = spi_controller_get_devdata(ctlr);
 	int status = 0;

 	if (bitbang->setup_transfer) {
 		status = bitbang->setup_transfer(spi, transfer);
 		if (status < 0)
 			goto out;
 	}

 	if (transfer->len)
 		status = bitbang->txrx_bufs(spi, transfer);

 	if (status == transfer->len)
 		status = 0;
 	else if (status >= 0)
 		status = -EREMOTEIO;

 out:
 	spi_finalize_current_transfer(ctlr);

 	return status;
 }

 static int spi_bitbang_unprepare_hardware(struct spi_controller *spi)
 {
 	struct spi_bitbang	*bitbang;

 	bitbang = spi_controller_get_devdata(spi);

 	mutex_lock(&bitbang->lock);
 	bitbang->busy = 0;
 	mutex_unlock(&bitbang->lock);

 	return 0;
 }

 static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
 {
 	struct spi_bitbang *bitbang = spi_controller_get_devdata(spi->controller);

 	/* SPI core provides CS high / low, but bitbang driver
 	 * expects CS active
 	 * spi device driver takes care of handling SPI_CS_HIGH
 	 */
 	enable = (!!(spi->mode & SPI_CS_HIGH) == enable);

 	ndelay(SPI_BITBANG_CS_DELAY);
 	bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
 			    BITBANG_CS_INACTIVE);
 	ndelay(SPI_BITBANG_CS_DELAY);
 }

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

 int spi_bitbang_init(struct spi_bitbang *bitbang)
 {
 	struct spi_controller *ctlr = bitbang->ctlr;
 	bool custom_cs;

 	if (!ctlr)
 		return -EINVAL;
 	/*
 	 * We only need the chipselect callback if we are actually using it.
 	 * If we just use GPIO descriptors, it is surplus. If the
 	 * SPI_CONTROLLER_GPIO_SS flag is set, we always need to call the
 	 * driver-specific chipselect routine.
 	 */
 	custom_cs = (!ctlr->use_gpio_descriptors ||
 		     (ctlr->flags & SPI_CONTROLLER_GPIO_SS));

 	if (custom_cs && !bitbang->chipselect)
 		return -EINVAL;

 	mutex_init(&bitbang->lock);

 	if (!ctlr->mode_bits)
 		ctlr->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;

 	if (ctlr->transfer || ctlr->transfer_one_message)
 		return -EINVAL;

 	ctlr->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
 	ctlr->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
 	ctlr->transfer_one = spi_bitbang_transfer_one;
 	/*
 	 * When using GPIO descriptors, the ->set_cs() callback doesn't even
 	 * get called unless SPI_CONTROLLER_GPIO_SS is set.
 	 */
 	if (custom_cs)
 		ctlr->set_cs = spi_bitbang_set_cs;

 	if (!bitbang->txrx_bufs) {
 		bitbang->use_dma = 0;
 		bitbang->txrx_bufs = spi_bitbang_bufs;
 		if (!ctlr->setup) {
 			if (!bitbang->setup_transfer)
 				bitbang->setup_transfer =
 					 spi_bitbang_setup_transfer;
 			ctlr->setup = spi_bitbang_setup;
 			ctlr->cleanup = spi_bitbang_cleanup;
 		}
 	}

 	return 0;
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_init);

 /**
  * spi_bitbang_start - start up a polled/bitbanging SPI host controller driver
  * @bitbang: driver handle
  *
  * Caller should have zero-initialized all parts of the structure, and then
  * provided callbacks for chip selection and I/O loops.  If the host controller has
  * a transfer method, its final step should call spi_bitbang_transfer(); or,
  * that's the default if the transfer routine is not initialized.  It should
  * also set up the bus number and number of chipselects.
  *
  * For i/o loops, provide callbacks either per-word (for bitbanging, or for
  * hardware that basically exposes a shift register) or per-spi_transfer
  * (which takes better advantage of hardware like fifos or DMA engines).
  *
  * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup(),
  * spi_bitbang_cleanup() and spi_bitbang_setup_transfer() to handle those SPI
  * host controller methods.  Those methods are the defaults if the bitbang->txrx_bufs
  * routine isn't initialized.
  *
  * This routine registers the spi_controller, which will process requests in a
  * dedicated task, keeping IRQs unblocked most of the time.  To stop
  * processing those requests, call spi_bitbang_stop().
  *
  * On success, this routine will take a reference to the controller. The caller
  * is responsible for calling spi_bitbang_stop() to decrement the reference and
  * spi_controller_put() as counterpart of spi_alloc_host() to prevent a memory
  * leak.
  */
 int spi_bitbang_start(struct spi_bitbang *bitbang)
 {
 	struct spi_controller *ctlr = bitbang->ctlr;
 	int ret;

 	ret = spi_bitbang_init(bitbang);
 	if (ret)
 		return ret;

 	/* driver may get busy before register() returns, especially
 	 * if someone registered boardinfo for devices
 	 */
 	ret = spi_register_controller(spi_controller_get(ctlr));
 	if (ret)
 		spi_controller_put(ctlr);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_start);

 /*
  * spi_bitbang_stop - stops the task providing spi communication
  */
 void spi_bitbang_stop(struct spi_bitbang *bitbang)
 {
 	spi_unregister_controller(bitbang->ctlr);
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_stop);

 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("Utilities for Bitbanging SPI host controllers");
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* Polling/bitbanging SPI host controller controller driver utilities
	*/

	#include <linux/spinlock.h>
	#include <linux/workqueue.h>
	#include <linux/interrupt.h>
	#include <linux/module.h>
	#include <linux/delay.h>
	#include <linux/errno.h>
	#include <linux/platform_device.h>
	#include <linux/slab.h>
	#include <linux/time64.h>

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

	#define SPI_BITBANG_CS_DELAY 100


	/----------------------------------------------------------------------/

	/*
	* FIRST PART (OPTIONAL): word-at-a-time spi_transfer support.
	* Use this for GPIO or shift-register level hardware APIs.
	*
	* spi_bitbang_cs is in spi_device->controller_state, which is unavailable
	* to glue code. These bitbang setup() and cleanup() routines are always
	* used, though maybe they're called from controller-aware code.
	*
	* chipselect() and friends may use spi_device->controller_data and
	* controller registers as appropriate.
	*
	*
	* NOTE: SPI controller pins can often be used as GPIO pins instead,
	* which means you could use a bitbang driver either to get hardware
	* working quickly, or testing for differences that aren't speed related.
	*/

	typedef unsigned int (spi_bb_txrx_bufs_fn)(struct spi_device , spi_bb_txrx_word_fn,
	unsigned int, struct spi_transfer *,
	unsigned int);

	struct spi_bitbang_cs {
	unsigned int nsecs; /* (clock cycle time) / 2 */
	spi_bb_txrx_word_fn txrx_word;
	spi_bb_txrx_bufs_fn txrx_bufs;
	};

	static unsigned int bitbang_txrx_8(struct spi_device *spi,
	spi_bb_txrx_word_fn txrx_word,
	unsigned int ns,
	struct spi_transfer *t,
	unsigned int flags)
	{
	struct spi_bitbang *bitbang;
	unsigned int bits = t->bits_per_word;
	unsigned int count = t->len;
	const u8 *tx = t->tx_buf;
	u8 *rx = t->rx_buf;

	bitbang = spi_controller_get_devdata(spi->controller);
	while (likely(count > 0)) {
	u8 word = 0;

	if (tx)
	word = *tx++;
	else
	word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFF : 0;
	word = txrx_word(spi, ns, word, bits, flags);
	if (rx)
	*rx++ = word;
	count -= 1;
	}
	if (bitbang->set_mosi_idle)
	bitbang->set_mosi_idle(spi);

	return t->len - count;
	}

	static unsigned int bitbang_txrx_16(struct spi_device *spi,
	spi_bb_txrx_word_fn txrx_word,
	unsigned int ns,
	struct spi_transfer *t,
	unsigned int flags)
	{
	struct spi_bitbang *bitbang;
	unsigned int bits = t->bits_per_word;
	unsigned int count = t->len;
	const u16 *tx = t->tx_buf;
	u16 *rx = t->rx_buf;

	bitbang = spi_controller_get_devdata(spi->controller);
	while (likely(count > 1)) {
	u16 word = 0;

	if (tx)
	word = *tx++;
	else
	word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFFFF : 0;
	word = txrx_word(spi, ns, word, bits, flags);
	if (rx)
	*rx++ = word;
	count -= 2;
	}
	if (bitbang->set_mosi_idle)
	bitbang->set_mosi_idle(spi);

	return t->len - count;
	}

	static unsigned int bitbang_txrx_32(struct spi_device *spi,
	spi_bb_txrx_word_fn txrx_word,
	unsigned int ns,
	struct spi_transfer *t,
	unsigned int flags)
	{
	struct spi_bitbang *bitbang;
	unsigned int bits = t->bits_per_word;
	unsigned int count = t->len;
	const u32 *tx = t->tx_buf;
	u32 *rx = t->rx_buf;

	bitbang = spi_controller_get_devdata(spi->controller);
	while (likely(count > 3)) {
	u32 word = 0;

	if (tx)
	word = *tx++;
	else
	word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFFFFFFFF : 0;
	word = txrx_word(spi, ns, word, bits, flags);
	if (rx)
	*rx++ = word;
	count -= 4;
	}
	if (bitbang->set_mosi_idle)
	bitbang->set_mosi_idle(spi);

	return t->len - count;
	}

	int spi_bitbang_setup_transfer(struct spi_device spi, struct spi_transfer t)
	{
	struct spi_bitbang_cs *cs = spi->controller_state;
	u8 bits_per_word;
	u32 hz;

	if (t) {
	bits_per_word = t->bits_per_word;
	hz = t->speed_hz;
	} else {
	bits_per_word = 0;
	hz = 0;
	}

	/* spi_transfer level calls that work per-word */
	if (!bits_per_word)
	bits_per_word = spi->bits_per_word;
	if (bits_per_word <= 8)
	cs->txrx_bufs = bitbang_txrx_8;
	else if (bits_per_word <= 16)
	cs->txrx_bufs = bitbang_txrx_16;
	else if (bits_per_word <= 32)
	cs->txrx_bufs = bitbang_txrx_32;
	else
	return -EINVAL;

	/* nsecs = (clock period)/2 */
	if (!hz)
	hz = spi->max_speed_hz;
	if (hz) {
	cs->nsecs = (NSEC_PER_SEC / 2) / hz;
	if (cs->nsecs > (MAX_UDELAY_MS * NSEC_PER_MSEC))
	return -EINVAL;
	}

	return 0;
	}
	EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);

	/*
	* spi_bitbang_setup - default setup for per-word I/O loops
	*/
	int spi_bitbang_setup(struct spi_device *spi)
	{
	struct spi_bitbang_cs *cs = spi->controller_state;
	struct spi_bitbang *bitbang;
	bool initial_setup = false;
	int retval;

	bitbang = spi_controller_get_devdata(spi->controller);

	if (!cs) {
	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
	if (!cs)
	return -ENOMEM;
	spi->controller_state = cs;
	initial_setup = true;
	}

	/* per-word shift register access, in hardware or bitbanging */
	cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL\|SPI_CPHA)];
	if (!cs->txrx_word) {
	retval = -EINVAL;
	goto err_free;
	}

	if (bitbang->setup_transfer) {
	retval = bitbang->setup_transfer(spi, NULL);
	if (retval < 0)
	goto err_free;
	}

	if (bitbang->set_mosi_idle)
	bitbang->set_mosi_idle(spi);

	dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);

	return 0;

	err_free:
	if (initial_setup)
	kfree(cs);
	return retval;
	}
	EXPORT_SYMBOL_GPL(spi_bitbang_setup);

	/*
	* spi_bitbang_cleanup - default cleanup for per-word I/O loops
	*/
	void spi_bitbang_cleanup(struct spi_device *spi)
	{
	kfree(spi->controller_state);
	}
	EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);

	static int spi_bitbang_bufs(struct spi_device spi, struct spi_transfer t)
	{
	struct spi_bitbang_cs *cs = spi->controller_state;
	unsigned int nsecs = cs->nsecs;
	struct spi_bitbang *bitbang;

	bitbang = spi_controller_get_devdata(spi->controller);
	if (bitbang->set_line_direction) {
	int err;

	err = bitbang->set_line_direction(spi, !!(t->tx_buf));
	if (err < 0)
	return err;
	}

	if (spi->mode & SPI_3WIRE) {
	unsigned int flags;

	flags = t->tx_buf ? SPI_CONTROLLER_NO_RX : SPI_CONTROLLER_NO_TX;
	return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
	}
	return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
	}

	/----------------------------------------------------------------------/

	/*
	* SECOND PART ... simple transfer queue runner.
	*
	* This costs a task context per controller, running the queue by
	* performing each transfer in sequence. Smarter hardware can queue
	* several DMA transfers at once, and process several controller queues
	* in parallel; this driver doesn't match such hardware very well.
	*
	* Drivers can provide word-at-a-time i/o primitives, or provide
	* transfer-at-a-time ones to leverage dma or fifo hardware.
	*/

	static int spi_bitbang_prepare_hardware(struct spi_controller *spi)
	{
	struct spi_bitbang *bitbang;

	bitbang = spi_controller_get_devdata(spi);

	mutex_lock(&bitbang->lock);
	bitbang->busy = 1;
	mutex_unlock(&bitbang->lock);

	return 0;
	}

	static int spi_bitbang_transfer_one(struct spi_controller *ctlr,
	struct spi_device *spi,
	struct spi_transfer *transfer)
	{
	struct spi_bitbang *bitbang = spi_controller_get_devdata(ctlr);
	int status = 0;

	if (bitbang->setup_transfer) {
	status = bitbang->setup_transfer(spi, transfer);
	if (status < 0)
	goto out;
	}

	if (transfer->len)
	status = bitbang->txrx_bufs(spi, transfer);

	if (status == transfer->len)
	status = 0;
	else if (status >= 0)
	status = -EREMOTEIO;

	out:
	spi_finalize_current_transfer(ctlr);

	return status;
	}

	static int spi_bitbang_unprepare_hardware(struct spi_controller *spi)
	{
	struct spi_bitbang *bitbang;

	bitbang = spi_controller_get_devdata(spi);

	mutex_lock(&bitbang->lock);
	bitbang->busy = 0;
	mutex_unlock(&bitbang->lock);

	return 0;
	}

	static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
	{
	struct spi_bitbang *bitbang = spi_controller_get_devdata(spi->controller);

	/* SPI core provides CS high / low, but bitbang driver
	* expects CS active
	* spi device driver takes care of handling SPI_CS_HIGH
	*/
	enable = (!!(spi->mode & SPI_CS_HIGH) == enable);

	ndelay(SPI_BITBANG_CS_DELAY);
	bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
	BITBANG_CS_INACTIVE);
	ndelay(SPI_BITBANG_CS_DELAY);
	}

	/----------------------------------------------------------------------/

	int spi_bitbang_init(struct spi_bitbang *bitbang)
	{
	struct spi_controller *ctlr = bitbang->ctlr;
	bool custom_cs;

	if (!ctlr)
	return -EINVAL;
	/*
	* We only need the chipselect callback if we are actually using it.
	* If we just use GPIO descriptors, it is surplus. If the
	* SPI_CONTROLLER_GPIO_SS flag is set, we always need to call the
	* driver-specific chipselect routine.
	*/
	custom_cs = (!ctlr->use_gpio_descriptors \|\|
	(ctlr->flags & SPI_CONTROLLER_GPIO_SS));

	if (custom_cs && !bitbang->chipselect)
	return -EINVAL;

	mutex_init(&bitbang->lock);

	if (!ctlr->mode_bits)
	ctlr->mode_bits = SPI_CPOL \| SPI_CPHA \| bitbang->flags;

	if (ctlr->transfer \|\| ctlr->transfer_one_message)
	return -EINVAL;

	ctlr->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
	ctlr->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
	ctlr->transfer_one = spi_bitbang_transfer_one;
	/*
	* When using GPIO descriptors, the ->set_cs() callback doesn't even
	* get called unless SPI_CONTROLLER_GPIO_SS is set.
	*/
	if (custom_cs)
	ctlr->set_cs = spi_bitbang_set_cs;

	if (!bitbang->txrx_bufs) {
	bitbang->use_dma = 0;
	bitbang->txrx_bufs = spi_bitbang_bufs;
	if (!ctlr->setup) {
	if (!bitbang->setup_transfer)
	bitbang->setup_transfer =
	spi_bitbang_setup_transfer;
	ctlr->setup = spi_bitbang_setup;
	ctlr->cleanup = spi_bitbang_cleanup;
	}
	}

	return 0;
	}
	EXPORT_SYMBOL_GPL(spi_bitbang_init);

	/**
	* spi_bitbang_start - start up a polled/bitbanging SPI host controller driver
	* @bitbang: driver handle
	*
	* Caller should have zero-initialized all parts of the structure, and then
	* provided callbacks for chip selection and I/O loops. If the host controller has
	* a transfer method, its final step should call spi_bitbang_transfer(); or,
	* that's the default if the transfer routine is not initialized. It should
	* also set up the bus number and number of chipselects.
	*
	* For i/o loops, provide callbacks either per-word (for bitbanging, or for
	* hardware that basically exposes a shift register) or per-spi_transfer
	* (which takes better advantage of hardware like fifos or DMA engines).
	*
	* Drivers using per-word I/O loops should use (or call) spi_bitbang_setup(),
	* spi_bitbang_cleanup() and spi_bitbang_setup_transfer() to handle those SPI
	* host controller methods. Those methods are the defaults if the bitbang->txrx_bufs
	* routine isn't initialized.
	*
	* This routine registers the spi_controller, which will process requests in a
	* dedicated task, keeping IRQs unblocked most of the time. To stop
	* processing those requests, call spi_bitbang_stop().
	*
	* On success, this routine will take a reference to the controller. The caller
	* is responsible for calling spi_bitbang_stop() to decrement the reference and
	* spi_controller_put() as counterpart of spi_alloc_host() to prevent a memory
	* leak.
	*/
	int spi_bitbang_start(struct spi_bitbang *bitbang)
	{
	struct spi_controller *ctlr = bitbang->ctlr;
	int ret;

	ret = spi_bitbang_init(bitbang);
	if (ret)
	return ret;

	/* driver may get busy before register() returns, especially
	* if someone registered boardinfo for devices
	*/
	ret = spi_register_controller(spi_controller_get(ctlr));
	if (ret)
	spi_controller_put(ctlr);

	return ret;
	}
	EXPORT_SYMBOL_GPL(spi_bitbang_start);

	/*
	* spi_bitbang_stop - stops the task providing spi communication
	*/
	void spi_bitbang_stop(struct spi_bitbang *bitbang)
	{
	spi_unregister_controller(bitbang->ctlr);
	}
	EXPORT_SYMBOL_GPL(spi_bitbang_stop);

	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("Utilities for Bitbanging SPI host controllers");