/*
 * 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.
 */

#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/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.
 */

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 = t->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 = t->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 = t->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;

        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;

        if (bitbang->setup_transfer) {
                int 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) */
        mutex_lock(&bitbang->lock);
        if (!bitbang->busy) {
                bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
                ndelay(cs->nsecs);
        }
        mutex_unlock(&bitbang->lock);

        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 int spi_bitbang_prepare_hardware(struct spi_master *spi)
{
        struct spi_bitbang      *bitbang;

        bitbang = spi_master_get_devdata(spi);

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

        return 0;
}

static int spi_bitbang_transfer_one(struct spi_master *master,
                                    struct spi_device *spi,
                                    struct spi_transfer *transfer)
{
        struct spi_bitbang *bitbang = spi_master_get_devdata(master);
        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(master);

        return status;
}

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

        bitbang = spi_master_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_master_get_devdata(spi->master);

        /* 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);
}

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

/**
 * 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().
 *
 * On success, this routine will take a reference to master. The caller is
 * responsible for calling spi_bitbang_stop() to decrement the reference and
 * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory
 * leak.
 */
int spi_bitbang_start(struct spi_bitbang *bitbang)
{
        struct spi_master *master = bitbang->master;
        int ret;

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

        mutex_init(&bitbang->lock);

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

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

        master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
        master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
        master->transfer_one = spi_bitbang_transfer_one;
        master->set_cs = spi_bitbang_set_cs;

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

        /* driver may get busy before register() returns, especially
         * if someone registered boardinfo for devices
         */
        ret = spi_register_master(spi_master_get(master));
        if (ret)
                spi_master_put(master);

        return 0;
}
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_master(bitbang->master);
}
EXPORT_SYMBOL_GPL(spi_bitbang_stop);

MODULE_LICENSE("GPL");