drivers/siox/siox-bus-gpio.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <kernel@pengutronix.de>
 */

#include <linux/gpio/consumer.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>

#include <linux/delay.h>

#include "siox.h"

#define DRIVER_NAME "siox-gpio"

struct siox_gpio_ddata {
	struct gpio_desc *din;
	struct gpio_desc *dout;
	struct gpio_desc *dclk;
	struct gpio_desc *dld;
};

static unsigned int siox_clkhigh_ns = 1000;
static unsigned int siox_loadhigh_ns;
static unsigned int siox_bytegap_ns;

static int siox_gpio_pushpull(struct siox_master *smaster,
			      size_t setbuf_len, const u8 setbuf[],
			      size_t getbuf_len, u8 getbuf[])
{
	struct siox_gpio_ddata *ddata = siox_master_get_devdata(smaster);
	size_t i;
	size_t cycles = max(setbuf_len, getbuf_len);

	/* reset data and clock */
	gpiod_set_value_cansleep(ddata->dout, 0);
	gpiod_set_value_cansleep(ddata->dclk, 0);

	gpiod_set_value_cansleep(ddata->dld, 1);
	ndelay(siox_loadhigh_ns);
	gpiod_set_value_cansleep(ddata->dld, 0);

	for (i = 0; i < cycles; ++i) {
		u8 set = 0, get = 0;
		size_t j;

		if (i >= cycles - setbuf_len)
			set = setbuf[i - (cycles - setbuf_len)];

		for (j = 0; j < 8; ++j) {
			get <<= 1;
			if (gpiod_get_value_cansleep(ddata->din))
				get |= 1;

			/* DOUT is logically inverted */
			gpiod_set_value_cansleep(ddata->dout, !(set & 0x80));
			set <<= 1;

			gpiod_set_value_cansleep(ddata->dclk, 1);
			ndelay(siox_clkhigh_ns);
			gpiod_set_value_cansleep(ddata->dclk, 0);
		}

		if (i < getbuf_len)
			getbuf[i] = get;

		ndelay(siox_bytegap_ns);
	}

	gpiod_set_value_cansleep(ddata->dld, 1);
	ndelay(siox_loadhigh_ns);
	gpiod_set_value_cansleep(ddata->dld, 0);

	/*
	 * Resetting dout isn't necessary protocol wise, but it makes the
	 * signals more pretty because the dout level is deterministic between
	 * cycles. Note that this only affects dout between the master and the
	 * first siox device. dout for the later devices depend on the output of
	 * the previous siox device.
	 */
	gpiod_set_value_cansleep(ddata->dout, 0);

	return 0;
}

static int siox_gpio_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct siox_gpio_ddata *ddata;
	int ret;
	struct siox_master *smaster;

	smaster = devm_siox_master_alloc(dev, sizeof(*ddata));
	if (!smaster)
		return dev_err_probe(dev, -ENOMEM,
				     "failed to allocate siox master\n");

	platform_set_drvdata(pdev, smaster);
	ddata = siox_master_get_devdata(smaster);

	ddata->din = devm_gpiod_get(dev, "din", GPIOD_IN);
	if (IS_ERR(ddata->din))
		return dev_err_probe(dev, PTR_ERR(ddata->din),
				     "Failed to get din GPIO\n");

	ddata->dout = devm_gpiod_get(dev, "dout", GPIOD_OUT_LOW);
	if (IS_ERR(ddata->dout))
		return dev_err_probe(dev, PTR_ERR(ddata->dout),
				     "Failed to get dout GPIO\n");

	ddata->dclk = devm_gpiod_get(dev, "dclk", GPIOD_OUT_LOW);
	if (IS_ERR(ddata->dclk))
		return dev_err_probe(dev, PTR_ERR(ddata->dclk),
				     "Failed to get dclk GPIO\n");

	ddata->dld = devm_gpiod_get(dev, "dld", GPIOD_OUT_LOW);
	if (IS_ERR(ddata->dld))
		return dev_err_probe(dev, PTR_ERR(ddata->dld),
				     "Failed to get dld GPIO\n");

	smaster->pushpull = siox_gpio_pushpull;
	/* XXX: determine automatically like spi does */
	smaster->busno = 0;

	ret = devm_siox_master_register(dev, smaster);
	if (ret)
		return dev_err_probe(dev, ret,
				     "Failed to register siox master\n");

	return 0;
}

static const struct of_device_id siox_gpio_dt_ids[] = {
	{ .compatible = "eckelmann,siox-gpio", },
	{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, siox_gpio_dt_ids);

static struct platform_driver siox_gpio_driver = {
	.probe = siox_gpio_probe,

	.driver = {
		.name = DRIVER_NAME,
		.of_match_table = siox_gpio_dt_ids,
	},
};
module_platform_driver(siox_gpio_driver);

MODULE_AUTHOR("Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>");
MODULE_DESCRIPTION("SIOX GPIO bus driver");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:" DRIVER_NAME);