/*
 * NBUS driver for TS-4600 based boards
 *
 * Copyright (c) 2016 - Savoir-faire Linux
 * Author: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
 *
 * This file is licensed under the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 *
 * This driver implements a GPIOs bit-banged bus, called the NBUS by Technologic
 * Systems. It is used to communicate with the peripherals in the FPGA on the
 * TS-4600 SoM.
 */

#include <linux/bitops.h>
#include <linux/gpio/consumer.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of_platform.h>
#include <linux/platform_device.h>
#include <linux/pwm.h>
#include <linux/ts-nbus.h>

#define TS_NBUS_DIRECTION_IN  0
#define TS_NBUS_DIRECTION_OUT 1
#define TS_NBUS_WRITE_ADR 0
#define TS_NBUS_WRITE_VAL 1

struct ts_nbus {
        struct pwm_device *pwm;
        struct gpio_descs *data;
        struct gpio_desc *csn;
        struct gpio_desc *txrx;
        struct gpio_desc *strobe;
        struct gpio_desc *ale;
        struct gpio_desc *rdy;
        struct mutex lock;
};

/*
 * request all gpios required by the bus.
 */
static int ts_nbus_init_pdata(struct platform_device *pdev, struct ts_nbus
                *ts_nbus)
{
        ts_nbus->data = devm_gpiod_get_array(&pdev->dev, "ts,data",
                        GPIOD_OUT_HIGH);
        if (IS_ERR(ts_nbus->data)) {
                dev_err(&pdev->dev, "failed to retrieve ts,data-gpio from dts\n");
                return PTR_ERR(ts_nbus->data);
        }

        ts_nbus->csn = devm_gpiod_get(&pdev->dev, "ts,csn", GPIOD_OUT_HIGH);
        if (IS_ERR(ts_nbus->csn)) {
                dev_err(&pdev->dev, "failed to retrieve ts,csn-gpio from dts\n");
                return PTR_ERR(ts_nbus->csn);
        }

        ts_nbus->txrx = devm_gpiod_get(&pdev->dev, "ts,txrx", GPIOD_OUT_HIGH);
        if (IS_ERR(ts_nbus->txrx)) {
                dev_err(&pdev->dev, "failed to retrieve ts,txrx-gpio from dts\n");
                return PTR_ERR(ts_nbus->txrx);
        }

        ts_nbus->strobe = devm_gpiod_get(&pdev->dev, "ts,strobe", GPIOD_OUT_HIGH);
        if (IS_ERR(ts_nbus->strobe)) {
                dev_err(&pdev->dev, "failed to retrieve ts,strobe-gpio from dts\n");
                return PTR_ERR(ts_nbus->strobe);
        }

        ts_nbus->ale = devm_gpiod_get(&pdev->dev, "ts,ale", GPIOD_OUT_HIGH);
        if (IS_ERR(ts_nbus->ale)) {
                dev_err(&pdev->dev, "failed to retrieve ts,ale-gpio from dts\n");
                return PTR_ERR(ts_nbus->ale);
        }

        ts_nbus->rdy = devm_gpiod_get(&pdev->dev, "ts,rdy", GPIOD_IN);
        if (IS_ERR(ts_nbus->rdy)) {
                dev_err(&pdev->dev, "failed to retrieve ts,rdy-gpio from dts\n");
                return PTR_ERR(ts_nbus->rdy);
        }

        return 0;
}

/*
 * the data gpios are used for reading and writing values, their directions
 * should be adjusted accordingly.
 */
static void ts_nbus_set_direction(struct ts_nbus *ts_nbus, int direction)
{
        int i;

        for (i = 0; i < 8; i++) {
                if (direction == TS_NBUS_DIRECTION_IN)
                        gpiod_direction_input(ts_nbus->data->desc[i]);
                else
                        /* when used as output the default state of the data
                         * lines are set to high */
                        gpiod_direction_output(ts_nbus->data->desc[i], 1);
        }
}

/*
 * reset the bus in its initial state.
 * The data, csn, strobe and ale lines must be zero'ed to let the FPGA knows a
 * new transaction can be process.
 */
static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus)
{
        DECLARE_BITMAP(values, 8);

        values[0] = 0;

        gpiod_set_array_value_cansleep(8, ts_nbus->data->desc,
                                       ts_nbus->data->info, values);
        gpiod_set_value_cansleep(ts_nbus->csn, 0);
        gpiod_set_value_cansleep(ts_nbus->strobe, 0);
        gpiod_set_value_cansleep(ts_nbus->ale, 0);
}

/*
 * let the FPGA knows it can process.
 */
static void ts_nbus_start_transaction(struct ts_nbus *ts_nbus)
{
        gpiod_set_value_cansleep(ts_nbus->strobe, 1);
}

/*
 * read a byte value from the data gpios.
 * return 0 on success or negative errno on failure.
 */
static int ts_nbus_read_byte(struct ts_nbus *ts_nbus, u8 *val)
{
        struct gpio_descs *gpios = ts_nbus->data;
        int ret, i;

        *val = 0;
        for (i = 0; i < 8; i++) {
                ret = gpiod_get_value_cansleep(gpios->desc[i]);
                if (ret < 0)
                        return ret;
                if (ret)
                        *val |= BIT(i);
        }

        return 0;
}

/*
 * set the data gpios accordingly to the byte value.
 */
static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte)
{
        struct gpio_descs *gpios = ts_nbus->data;
        DECLARE_BITMAP(values, 8);

        values[0] = byte;

        gpiod_set_array_value_cansleep(8, gpios->desc, gpios->info, values);
}

/*
 * reading the bus consists of resetting the bus, then notifying the FPGA to
 * send the data in the data gpios and return the read value.
 * return 0 on success or negative errno on failure.
 */
static int ts_nbus_read_bus(struct ts_nbus *ts_nbus, u8 *val)
{
        ts_nbus_reset_bus(ts_nbus);
        ts_nbus_start_transaction(ts_nbus);

        return ts_nbus_read_byte(ts_nbus, val);
}

/*
 * writing to the bus consists of resetting the bus, then define the type of
 * command (address/value), write the data and notify the FPGA to retrieve the
 * value in the data gpios.
 */
static void ts_nbus_write_bus(struct ts_nbus *ts_nbus, int cmd, u8 val)
{
        ts_nbus_reset_bus(ts_nbus);

        if (cmd == TS_NBUS_WRITE_ADR)
                gpiod_set_value_cansleep(ts_nbus->ale, 1);

        ts_nbus_write_byte(ts_nbus, val);
        ts_nbus_start_transaction(ts_nbus);
}

/*
 * read the value in the FPGA register at the given address.
 * return 0 on success or negative errno on failure.
 */
int ts_nbus_read(struct ts_nbus *ts_nbus, u8 adr, u16 *val)
{
        int ret, i;
        u8 byte;

        /* bus access must be atomic */
        mutex_lock(&ts_nbus->lock);

        /* set the bus in read mode */
        gpiod_set_value_cansleep(ts_nbus->txrx, 0);

        /* write address */
        ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_ADR, adr);

        /* set the data gpios direction as input before reading */
        ts_nbus_set_direction(ts_nbus, TS_NBUS_DIRECTION_IN);

        /* reading value MSB first */
        do {
                *val = 0;
                byte = 0;
                for (i = 1; i >= 0; i--) {
                        /* read a byte from the bus, leave on error */
                        ret = ts_nbus_read_bus(ts_nbus, &byte);
                        if (ret < 0)
                                goto err;

                        /* append the byte read to the final value */
                        *val |= byte << (i * 8);
                }
                gpiod_set_value_cansleep(ts_nbus->csn, 1);
                ret = gpiod_get_value_cansleep(ts_nbus->rdy);
        } while (ret);

err:
        /* restore the data gpios direction as output after reading */
        ts_nbus_set_direction(ts_nbus, TS_NBUS_DIRECTION_OUT);

        mutex_unlock(&ts_nbus->lock);

        return ret;
}
EXPORT_SYMBOL_GPL(ts_nbus_read);

/*
 * write the desired value in the FPGA register at the given address.
 */
int ts_nbus_write(struct ts_nbus *ts_nbus, u8 adr, u16 val)
{
        int i;

        /* bus access must be atomic */
        mutex_lock(&ts_nbus->lock);

        /* set the bus in write mode */
        gpiod_set_value_cansleep(ts_nbus->txrx, 1);

        /* write address */
        ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_ADR, adr);

        /* writing value MSB first */
        for (i = 1; i >= 0; i--)
                ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_VAL, (u8)(val >> (i * 8)));

        /* wait for completion */
        gpiod_set_value_cansleep(ts_nbus->csn, 1);
        while (gpiod_get_value_cansleep(ts_nbus->rdy) != 0) {
                gpiod_set_value_cansleep(ts_nbus->csn, 0);
                gpiod_set_value_cansleep(ts_nbus->csn, 1);
        }

        mutex_unlock(&ts_nbus->lock);

        return 0;
}
EXPORT_SYMBOL_GPL(ts_nbus_write);

static int ts_nbus_probe(struct platform_device *pdev)
{
        struct pwm_device *pwm;
        struct pwm_args pargs;
        struct device *dev = &pdev->dev;
        struct ts_nbus *ts_nbus;
        int ret;

        ts_nbus = devm_kzalloc(dev, sizeof(*ts_nbus), GFP_KERNEL);
        if (!ts_nbus)
                return -ENOMEM;

        mutex_init(&ts_nbus->lock);

        ret = ts_nbus_init_pdata(pdev, ts_nbus);
        if (ret < 0)
                return ret;

        pwm = devm_pwm_get(dev, NULL);
        if (IS_ERR(pwm)) {
                ret = PTR_ERR(pwm);
                if (ret != -EPROBE_DEFER)
                        dev_err(dev, "unable to request PWM\n");
                return ret;
        }

        pwm_get_args(pwm, &pargs);
        if (!pargs.period) {
                dev_err(&pdev->dev, "invalid PWM period\n");
                return -EINVAL;
        }

        /*
         * FIXME: pwm_apply_args() should be removed when switching to
         * the atomic PWM API.
         */
        pwm_apply_args(pwm);
        ret = pwm_config(pwm, pargs.period, pargs.period);
        if (ret < 0)
                return ret;

        /*
         * we can now start the FPGA and populate the peripherals.
         */
        pwm_enable(pwm);
        ts_nbus->pwm = pwm;

        /*
         * let the child nodes retrieve this instance of the ts-nbus.
         */
        dev_set_drvdata(dev, ts_nbus);

        ret = of_platform_populate(dev->of_node, NULL, NULL, dev);
        if (ret < 0)
                return ret;

        dev_info(dev, "initialized\n");

        return 0;
}

static int ts_nbus_remove(struct platform_device *pdev)
{
        struct ts_nbus *ts_nbus = dev_get_drvdata(&pdev->dev);

        /* shutdown the FPGA */
        mutex_lock(&ts_nbus->lock);
        pwm_disable(ts_nbus->pwm);
        mutex_unlock(&ts_nbus->lock);

        return 0;
}

static const struct of_device_id ts_nbus_of_match[] = {
        { .compatible = "technologic,ts-nbus", },
        { },
};
MODULE_DEVICE_TABLE(of, ts_nbus_of_match);

static struct platform_driver ts_nbus_driver = {
        .probe          = ts_nbus_probe,
        .remove         = ts_nbus_remove,
        .driver         = {
                .name   = "ts_nbus",
                .of_match_table = ts_nbus_of_match,
        },
};

module_platform_driver(ts_nbus_driver);

MODULE_ALIAS("platform:ts_nbus");
MODULE_AUTHOR("Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>");
MODULE_DESCRIPTION("Technologic Systems NBUS");
MODULE_LICENSE("GPL v2");