// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * SPI master driver using generic bitbanged GPIO
 *
 * Copyright (C) 2006,2008 David Brownell
 * Copyright (C) 2017 Linus Walleij
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>
#include <linux/of_device.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->master->dev.driver_data ... points to spi_gpio->bitbang
 */

struct spi_gpio {
        struct spi_bitbang              bitbang;
        struct gpio_desc                *sck;
        struct gpio_desc                *miso;
        struct gpio_desc                *mosi;
        struct gpio_desc                **cs_gpios;
};

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

/*
 * 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 */

#endif

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

static inline struct spi_gpio *__pure
spi_to_spi_gpio(const struct spi_device *spi)
{
        const struct spi_bitbang        *bang;
        struct spi_gpio                 *spi_gpio;

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

/* These helpers are in turn called by the bitbang inlines */
static inline void setsck(const struct spi_device *spi, int is_on)
{
        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

        gpiod_set_value_cansleep(spi_gpio->sck, is_on);
}

static inline void setmosi(const struct spi_device *spi, int is_on)
{
        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

        gpiod_set_value_cansleep(spi_gpio->mosi, is_on);
}

static inline int getmiso(const struct spi_device *spi)
{
        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

        if (spi->mode & SPI_3WIRE)
                return !!gpiod_get_value_cansleep(spi_gpio->mosi);
        else
                return !!gpiod_get_value_cansleep(spi_gpio->miso);
}

/*
 * 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, unsigned flags)
{
        return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
                unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
        return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
                unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
        return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}

static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
                unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
        return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, 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)
{
        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)
{
        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)
{
        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)
{
        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)
{
        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

        /* set initial clock line level */
        if (is_active)
                gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);

        /* Drive chip select line, if we have one */
        if (spi_gpio->cs_gpios) {
                struct gpio_desc *cs = spi_gpio->cs_gpios[spi->chip_select];

                /* SPI chip selects are normally active-low */
                gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
        }
}

static int spi_gpio_setup(struct spi_device *spi)
{
        struct gpio_desc        *cs;
        int                     status = 0;
        struct spi_gpio         *spi_gpio = spi_to_spi_gpio(spi);

        /*
         * The CS GPIOs have already been
         * initialized from the descriptor lookup.
         */
        if (spi_gpio->cs_gpios) {
                cs = spi_gpio->cs_gpios[spi->chip_select];
                if (!spi->controller_state && cs)
                        status = gpiod_direction_output(cs,
                                                  !(spi->mode & SPI_CS_HIGH));
        }

        if (!status)
                status = spi_bitbang_setup(spi);

        return status;
}

static int spi_gpio_set_direction(struct spi_device *spi, bool output)
{
        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
        int ret;

        if (output)
                return gpiod_direction_output(spi_gpio->mosi, 1);

        ret = gpiod_direction_input(spi_gpio->mosi);
        if (ret)
                return ret;
        /*
         * Send a turnaround high impedance cycle when switching
         * from output to input. Theoretically there should be
         * a clock delay here, but as has been noted above, the
         * nsec delay function for bit-banged GPIO is simply
         * {} because bit-banging just doesn't get fast enough
         * anyway.
         */
        if (spi->mode & SPI_3WIRE_HIZ) {
                gpiod_set_value_cansleep(spi_gpio->sck,
                                         !(spi->mode & SPI_CPOL));
                gpiod_set_value_cansleep(spi_gpio->sck,
                                         !!(spi->mode & SPI_CPOL));
        }
        return 0;
}

static void spi_gpio_cleanup(struct spi_device *spi)
{
        spi_bitbang_cleanup(spi);
}

/*
 * It can be convenient to use this driver with pins that have alternate
 * functions associated with a "native" SPI controller if a driver for that
 * controller is not available, or is missing important functionality.
 *
 * On platforms which can do so, configure MISO with a weak pullup unless
 * there's an external pullup on that signal.  That saves power by avoiding
 * floating signals.  (A weak pulldown would save power too, but many
 * drivers expect to see all-ones data as the no slave "response".)
 */
static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
{
        spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW);
        if (IS_ERR(spi_gpio->mosi))
                return PTR_ERR(spi_gpio->mosi);

        spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
        if (IS_ERR(spi_gpio->miso))
                return PTR_ERR(spi_gpio->miso);

        spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
        return PTR_ERR_OR_ZERO(spi_gpio->sck);
}

#ifdef CONFIG_OF
static const struct of_device_id spi_gpio_dt_ids[] = {
        { .compatible = "spi-gpio" },
        {}
};
MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);

static int spi_gpio_probe_dt(struct platform_device *pdev,
                             struct spi_master *master)
{
        master->dev.of_node = pdev->dev.of_node;
        master->use_gpio_descriptors = true;

        return 0;
}
#else
static inline int spi_gpio_probe_dt(struct platform_device *pdev,
                                    struct spi_master *master)
{
        return 0;
}
#endif

static int spi_gpio_probe_pdata(struct platform_device *pdev,
                                struct spi_master *master)
{
        struct device *dev = &pdev->dev;
        struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
        struct spi_gpio *spi_gpio = spi_master_get_devdata(master);
        int i;

#ifdef GENERIC_BITBANG
        if (!pdata || !pdata->num_chipselect)
                return -ENODEV;
#endif
        /*
         * The master needs to think there is a chipselect even if not
         * connected
         */
        master->num_chipselect = pdata->num_chipselect ?: 1;

        spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect,
                                          sizeof(*spi_gpio->cs_gpios),
                                          GFP_KERNEL);
        if (!spi_gpio->cs_gpios)
                return -ENOMEM;

        for (i = 0; i < master->num_chipselect; i++) {
                spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
                                                             GPIOD_OUT_HIGH);
                if (IS_ERR(spi_gpio->cs_gpios[i]))
                        return PTR_ERR(spi_gpio->cs_gpios[i]);
        }

        return 0;
}

static int spi_gpio_probe(struct platform_device *pdev)
{
        int                             status;
        struct spi_master               *master;
        struct spi_gpio                 *spi_gpio;
        struct device                   *dev = &pdev->dev;
        struct spi_bitbang              *bb;

        master = devm_spi_alloc_master(dev, sizeof(*spi_gpio));
        if (!master)
                return -ENOMEM;

        if (pdev->dev.of_node)
                status = spi_gpio_probe_dt(pdev, master);
        else
                status = spi_gpio_probe_pdata(pdev, master);

        if (status)
                return status;

        spi_gpio = spi_master_get_devdata(master);

        status = spi_gpio_request(dev, spi_gpio);
        if (status)
                return status;

        master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
        master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
                            SPI_CS_HIGH;
        if (!spi_gpio->mosi) {
                /* HW configuration without MOSI pin
                 *
                 * No setting SPI_MASTER_NO_RX here - if there is only
                 * a MOSI pin connected the host can still do RX by
                 * changing the direction of the line.
                 */
                master->flags = SPI_MASTER_NO_TX;
        }

        master->bus_num = pdev->id;
        master->setup = spi_gpio_setup;
        master->cleanup = spi_gpio_cleanup;

        bb = &spi_gpio->bitbang;
        bb->master = master;
        /*
         * There is some additional business, apart from driving the CS GPIO
         * line, that we need to do on selection. This makes the local
         * callback for chipselect always get called.
         */
        master->flags |= SPI_MASTER_GPIO_SS;
        bb->chipselect = spi_gpio_chipselect;
        bb->set_line_direction = spi_gpio_set_direction;

        if (master->flags & SPI_MASTER_NO_TX) {
                bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
                bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
                bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
                bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
        } else {
                bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
                bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
                bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
                bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
        }
        bb->setup_transfer = spi_bitbang_setup_transfer;

        status = spi_bitbang_init(&spi_gpio->bitbang);
        if (status)
                return status;

        return devm_spi_register_master(&pdev->dev, master);
}

MODULE_ALIAS("platform:" DRIVER_NAME);

static struct platform_driver spi_gpio_driver = {
        .driver = {
                .name   = DRIVER_NAME,
                .of_match_table = of_match_ptr(spi_gpio_dt_ids),
        },
        .probe          = spi_gpio_probe,
};
module_platform_driver(spi_gpio_driver);

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