ts-nbus.c

/*
 * 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");