/*
 * spi_bitbang.c - polling/bitbanging SPI master controller driver utilities
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/workqueue.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/platform_device.h>

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


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

/*
 * 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 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.
 */

struct spi_bitbang_cs {
        unsigned        nsecs;  /* (clock cycle time)/2 */
        u32             (*txrx_word)(struct spi_device *spi, unsigned nsecs,
                                        u32 word, u8 bits);
        unsigned        (*txrx_bufs)(struct spi_device *,
                                        u32 (*txrx_word)(
                                                struct spi_device *spi,
                                                unsigned nsecs,
                                                u32 word, u8 bits),
                                        unsigned, struct spi_transfer *);
};

static unsigned bitbang_txrx_8(
        struct spi_device       *spi,
        u32                     (*txrx_word)(struct spi_device *spi,
                                        unsigned nsecs,
                                        u32 word, u8 bits),
        unsigned                ns,
        struct spi_transfer     *t
) {
        unsigned                bits = spi->bits_per_word;
        unsigned                count = t->len;
        const u8                *tx = t->tx_buf;
        u8                      *rx = t->rx_buf;

        while (likely(count > 0)) {
                u8              word = 0;

                if (tx)
                        word = *tx++;
                word = txrx_word(spi, ns, word, bits);
                if (rx)
                        *rx++ = word;
                count -= 1;
        }
        return t->len - count;
}

static unsigned bitbang_txrx_16(
        struct spi_device       *spi,
        u32                     (*txrx_word)(struct spi_device *spi,
                                        unsigned nsecs,
                                        u32 word, u8 bits),
        unsigned                ns,
        struct spi_transfer     *t
) {
        unsigned                bits = spi->bits_per_word;
        unsigned                count = t->len;
        const u16               *tx = t->tx_buf;
        u16                     *rx = t->rx_buf;

        while (likely(count > 1)) {
                u16             word = 0;

                if (tx)
                        word = *tx++;
                word = txrx_word(spi, ns, word, bits);
                if (rx)
                        *rx++ = word;
                count -= 2;
        }
        return t->len - count;
}

static unsigned bitbang_txrx_32(
        struct spi_device       *spi,
        u32                     (*txrx_word)(struct spi_device *spi,
                                        unsigned nsecs,
                                        u32 word, u8 bits),
        unsigned                ns,
        struct spi_transfer     *t
) {
        unsigned                bits = spi->bits_per_word;
        unsigned                count = t->len;
        const u32               *tx = t->tx_buf;
        u32                     *rx = t->rx_buf;

        while (likely(count > 3)) {
                u32             word = 0;

                if (tx)
                        word = *tx++;
                word = txrx_word(spi, ns, word, bits);
                if (rx)
                        *rx++ = word;
                count -= 4;
        }
        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 = (1000000000/2) / hz;
                if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
                        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;
        int                     retval;
        unsigned long           flags;

        bitbang = spi_master_get_devdata(spi->master);

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

        /* 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)
                return -EINVAL;

        retval = bitbang->setup_transfer(spi, NULL);
        if (retval < 0)
                return retval;

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

        /* NOTE we _need_ to call chipselect() early, ideally with adapter
         * setup, unless the hardware defaults cooperate to avoid confusion
         * between normal (active low) and inverted chipselects.
         */

        /* deselect chip (low or high) */
        spin_lock_irqsave(&bitbang->lock, flags);
        if (!bitbang->busy) {
                bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
                ndelay(cs->nsecs);
        }
        spin_unlock_irqrestore(&bitbang->lock, flags);

        return 0;
}
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                nsecs = cs->nsecs;

        return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t);
}

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

/*
 * 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 void bitbang_work(struct work_struct *work)
{
        struct spi_bitbang      *bitbang =
                container_of(work, struct spi_bitbang, work);
        unsigned long           flags;
        int                     do_setup = -1;
        int                     (*setup_transfer)(struct spi_device *,
                                        struct spi_transfer *);

        setup_transfer = bitbang->setup_transfer;

        spin_lock_irqsave(&bitbang->lock, flags);
        bitbang->busy = 1;
        while (!list_empty(&bitbang->queue)) {
                struct spi_message      *m;
                struct spi_device       *spi;
                unsigned                nsecs;
                struct spi_transfer     *t = NULL;
                unsigned                tmp;
                unsigned                cs_change;
                int                     status;

                m = container_of(bitbang->queue.next, struct spi_message,
                                queue);
                list_del_init(&m->queue);
                spin_unlock_irqrestore(&bitbang->lock, flags);

                /* FIXME this is made-up ... the correct value is known to
                 * word-at-a-time bitbang code, and presumably chipselect()
                 * should enforce these requirements too?
                 */
                nsecs = 100;

                spi = m->spi;
                tmp = 0;
                cs_change = 1;
                status = 0;

                list_for_each_entry (t, &m->transfers, transfer_list) {

                        /* override speed or wordsize? */
                        if (t->speed_hz || t->bits_per_word)
                                do_setup = 1;

                        /* init (-1) or override (1) transfer params */
                        if (do_setup != 0) {
                                if (!setup_transfer) {
                                        status = -ENOPROTOOPT;
                                        break;
                                }
                                status = setup_transfer(spi, t);
                                if (status < 0)
                                        break;
                        }

                        /* set up default clock polarity, and activate chip;
                         * this implicitly updates clock and spi modes as
                         * previously recorded for this device via setup().
                         * (and also deselects any other chip that might be
                         * selected ...)
                         */
                        if (cs_change) {
                                bitbang->chipselect(spi, BITBANG_CS_ACTIVE);
                                ndelay(nsecs);
                        }
                        cs_change = t->cs_change;
                        if (!t->tx_buf && !t->rx_buf && t->len) {
                                status = -EINVAL;
                                break;
                        }

                        /* transfer data.  the lower level code handles any
                         * new dma mappings it needs. our caller always gave
                         * us dma-safe buffers.
                         */
                        if (t->len) {
                                /* REVISIT dma API still needs a designated
                                 * DMA_ADDR_INVALID; ~0 might be better.
                                 */
                                if (!m->is_dma_mapped)
                                        t->rx_dma = t->tx_dma = 0;
                                status = bitbang->txrx_bufs(spi, t);
                        }
                        if (status > 0)
                                m->actual_length += status;
                        if (status != t->len) {
                                /* always report some kind of error */
                                if (status >= 0)
                                        status = -EREMOTEIO;
                                break;
                        }
                        status = 0;

                        /* protocol tweaks before next transfer */
                        if (t->delay_usecs)
                                udelay(t->delay_usecs);

                        if (!cs_change)
                                continue;
                        if (t->transfer_list.next == &m->transfers)
                                break;

                        /* sometimes a short mid-message deselect of the chip
                         * may be needed to terminate a mode or command
                         */
                        ndelay(nsecs);
                        bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
                        ndelay(nsecs);
                }

                m->status = status;
                m->complete(m->context);

                /* restore speed and wordsize if it was overridden */
                if (do_setup == 1)
                        setup_transfer(spi, NULL);
                do_setup = 0;

                /* normally deactivate chipselect ... unless no error and
                 * cs_change has hinted that the next message will probably
                 * be for this chip too.
                 */
                if (!(status == 0 && cs_change)) {
                        ndelay(nsecs);
                        bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
                        ndelay(nsecs);
                }

                spin_lock_irqsave(&bitbang->lock, flags);
        }
        bitbang->busy = 0;
        spin_unlock_irqrestore(&bitbang->lock, flags);
}

/**
 * spi_bitbang_transfer - default submit to transfer queue
 */
int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m)
{
        struct spi_bitbang      *bitbang;
        unsigned long           flags;
        int                     status = 0;

        m->actual_length = 0;
        m->status = -EINPROGRESS;

        bitbang = spi_master_get_devdata(spi->master);

        spin_lock_irqsave(&bitbang->lock, flags);
        if (!spi->max_speed_hz)
                status = -ENETDOWN;
        else {
                list_add_tail(&m->queue, &bitbang->queue);
                queue_work(bitbang->workqueue, &bitbang->work);
        }
        spin_unlock_irqrestore(&bitbang->lock, flags);

        return status;
}
EXPORT_SYMBOL_GPL(spi_bitbang_transfer);

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

/**
 * spi_bitbang_start - start up a polled/bitbanging SPI master 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 master 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
 * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
 * routine isn't initialized.
 *
 * This routine registers the spi_master, which will process requests in a
 * dedicated task, keeping IRQs unblocked most of the time.  To stop
 * processing those requests, call spi_bitbang_stop().
 */
int spi_bitbang_start(struct spi_bitbang *bitbang)
{
        int     status;

        if (!bitbang->master || !bitbang->chipselect)
                return -EINVAL;

        INIT_WORK(&bitbang->work, bitbang_work);
        spin_lock_init(&bitbang->lock);
        INIT_LIST_HEAD(&bitbang->queue);

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

        if (!bitbang->master->transfer)
                bitbang->master->transfer = spi_bitbang_transfer;
        if (!bitbang->txrx_bufs) {
                bitbang->use_dma = 0;
                bitbang->txrx_bufs = spi_bitbang_bufs;
                if (!bitbang->master->setup) {
                        if (!bitbang->setup_transfer)
                                bitbang->setup_transfer =
                                         spi_bitbang_setup_transfer;
                        bitbang->master->setup = spi_bitbang_setup;
                        bitbang->master->cleanup = spi_bitbang_cleanup;
                }
        } else if (!bitbang->master->setup)
                return -EINVAL;

        /* this task is the only thing to touch the SPI bits */
        bitbang->busy = 0;
        bitbang->workqueue = create_singlethread_workqueue(
                        dev_name(bitbang->master->dev.parent));
        if (bitbang->workqueue == NULL) {
                status = -EBUSY;
                goto err1;
        }

        /* driver may get busy before register() returns, especially
         * if someone registered boardinfo for devices
         */
        status = spi_register_master(bitbang->master);
        if (status < 0)
                goto err2;

        return status;

err2:
        destroy_workqueue(bitbang->workqueue);
err1:
        return status;
}
EXPORT_SYMBOL_GPL(spi_bitbang_start);

/**
 * spi_bitbang_stop - stops the task providing spi communication
 */
int spi_bitbang_stop(struct spi_bitbang *bitbang)
{
        spi_unregister_master(bitbang->master);

        WARN_ON(!list_empty(&bitbang->queue));

        destroy_workqueue(bitbang->workqueue);

        return 0;
}
EXPORT_SYMBOL_GPL(spi_bitbang_stop);

MODULE_LICENSE("GPL");