[linux-block.git] / drivers / i2c / muxes / i2c-arb-gpio-challenge.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
 *
 * Copyright (C) 2012 Google, Inc
 */

#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/kernel.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>


/**
 * struct i2c_arbitrator_data - Driver data for I2C arbitrator
 *
 * @our_gpio: GPIO descriptor we'll use to claim.
 * @their_gpio: GPIO descriptor that the other side will use to claim.
 * @slew_delay_us: microseconds to wait for a GPIO to go high.
 * @wait_retry_us: we'll attempt another claim after this many microseconds.
 * @wait_free_us: we'll give up after this many microseconds.
 */

struct i2c_arbitrator_data {
	struct gpio_desc *our_gpio;
	struct gpio_desc *their_gpio;
	unsigned int slew_delay_us;
	unsigned int wait_retry_us;
	unsigned int wait_free_us;
};


/*
 * i2c_arbitrator_select - claim the I2C bus
 *
 * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
 */
static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
{
	const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
	unsigned long stop_retry, stop_time;

	/* Start a round of trying to claim the bus */
	stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
	do {
		/* Indicate that we want to claim the bus */
		gpiod_set_value(arb->our_gpio, 1);
		udelay(arb->slew_delay_us);

		/* Wait for the other master to release it */
		stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
		while (time_before(jiffies, stop_retry)) {
			int gpio_val = gpiod_get_value(arb->their_gpio);

			if (!gpio_val) {
				/* We got it, so return */
				return 0;
			}

			usleep_range(50, 200);
		}

		/* It didn't release, so give up, wait, and try again */
		gpiod_set_value(arb->our_gpio, 0);

		usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
	} while (time_before(jiffies, stop_time));

	/* Give up, release our claim */
	gpiod_set_value(arb->our_gpio, 0);
	udelay(arb->slew_delay_us);
	dev_err(muxc->dev, "Could not claim bus, timeout\n");
	return -EBUSY;
}

/*
 * i2c_arbitrator_deselect - release the I2C bus
 *
 * Release the I2C bus using the GPIO-based signalling protocol.
 */
static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
{
	const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);

	/* Release the bus and wait for the other master to notice */
	gpiod_set_value(arb->our_gpio, 0);
	udelay(arb->slew_delay_us);

	return 0;
}

static int i2c_arbitrator_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct device_node *np = dev->of_node;
	struct device_node *parent_np;
	struct i2c_mux_core *muxc;
	struct i2c_arbitrator_data *arb;
	struct gpio_desc *dummy;
	int ret;

	/* We only support probing from device tree; no platform_data */
	if (!np) {
		dev_err(dev, "Cannot find device tree node\n");
		return -ENODEV;
	}
	if (dev_get_platdata(dev)) {
		dev_err(dev, "Platform data is not supported\n");
		return -EINVAL;
	}

	muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
			     i2c_arbitrator_select, i2c_arbitrator_deselect);
	if (!muxc)
		return -ENOMEM;
	arb = i2c_mux_priv(muxc);

	platform_set_drvdata(pdev, muxc);

	/* Request GPIOs, our GPIO as unclaimed to begin with */
	arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);
	if (IS_ERR(arb->our_gpio)) {
		dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",
			PTR_ERR(arb->our_gpio));
		return PTR_ERR(arb->our_gpio);
	}

	arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);
	if (IS_ERR(arb->their_gpio)) {
		dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",
			PTR_ERR(arb->their_gpio));
		return PTR_ERR(arb->their_gpio);
	}

	/* At the moment we only support a single two master (us + 1 other) */
	dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);
	if (!IS_ERR(dummy)) {
		dev_err(dev, "Only one other master is supported\n");
		return -EINVAL;
	} else if (PTR_ERR(dummy) == -EPROBE_DEFER) {
		return -EPROBE_DEFER;
	}

	/* Arbitration parameters */
	if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
		arb->slew_delay_us = 10;
	if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
		arb->wait_retry_us = 3000;
	if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
		arb->wait_free_us = 50000;

	/* Find our parent */
	parent_np = of_parse_phandle(np, "i2c-parent", 0);
	if (!parent_np) {
		dev_err(dev, "Cannot parse i2c-parent\n");
		return -EINVAL;
	}
	muxc->parent = of_get_i2c_adapter_by_node(parent_np);
	of_node_put(parent_np);
	if (!muxc->parent) {
		dev_err(dev, "Cannot find parent bus\n");
		return -EPROBE_DEFER;
	}

	/* Actually add the mux adapter */
	ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
	if (ret)
		i2c_put_adapter(muxc->parent);

	return ret;
}

static int i2c_arbitrator_remove(struct platform_device *pdev)
{
	struct i2c_mux_core *muxc = platform_get_drvdata(pdev);

	i2c_mux_del_adapters(muxc);
	i2c_put_adapter(muxc->parent);
	return 0;
}

static const struct of_device_id i2c_arbitrator_of_match[] = {
	{ .compatible = "i2c-arb-gpio-challenge", },
	{},
};
MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);

static struct platform_driver i2c_arbitrator_driver = {
	.probe	= i2c_arbitrator_probe,
	.remove	= i2c_arbitrator_remove,
	.driver	= {
		.name	= "i2c-arb-gpio-challenge",
		.of_match_table = i2c_arbitrator_of_match,
	},
};

module_platform_driver(i2c_arbitrator_driver);

MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:i2c-arb-gpio-challenge");
Commit	Line	Data
9c92ab61	1	// SPDX-License-Identifier: GPL-2.0-only
b81dfaa0 DA	2	/*
	3	* GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
	4	*
	5	* Copyright (C) 2012 Google, Inc
b81dfaa0 DA	6	*/
	7
	8	#include <linux/delay.h>
d9a183bf	9	#include <linux/gpio/consumer.h>
b81dfaa0 DA	10	#include <linux/kernel.h>
	11	#include <linux/i2c.h>
	12	#include <linux/i2c-mux.h>
b81dfaa0	13	#include <linux/module.h>
b81dfaa0 DA	14	#include <linux/platform_device.h>
	15	#include <linux/slab.h>
	16
	17
	18	/**
	19	* struct i2c_arbitrator_data - Driver data for I2C arbitrator
	20	*
d9a183bf LW	21	* @our_gpio: GPIO descriptor we'll use to claim.
d9a183bf LW	22	* @their_gpio: GPIO descriptor that the other side will use to claim.
b81dfaa0 DA	23	* @slew_delay_us: microseconds to wait for a GPIO to go high.
	24	* @wait_retry_us: we'll attempt another claim after this many microseconds.
	25	* @wait_free_us: we'll give up after this many microseconds.
	26	*/
	27
	28	struct i2c_arbitrator_data {
d9a183bf LW	29	struct gpio_desc *our_gpio;
d9a183bf LW	30	struct gpio_desc *their_gpio;
b81dfaa0 DA	31	unsigned int slew_delay_us;
	32	unsigned int wait_retry_us;
	33	unsigned int wait_free_us;
	34	};
	35
	36
45ce82f5	37	/*
b81dfaa0 DA	38	* i2c_arbitrator_select - claim the I2C bus
	39	*
	40	* Use the GPIO-based signalling protocol; return -EBUSY if we fail.
	41	*/
8aacd901	42	static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
b81dfaa0	43	{
8aacd901	44	const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
b81dfaa0 DA	45	unsigned long stop_retry, stop_time;
	46
	47	/* Start a round of trying to claim the bus */
	48	stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
	49	do {
	50	/* Indicate that we want to claim the bus */
d9a183bf	51	gpiod_set_value(arb->our_gpio, 1);
b81dfaa0 DA	52	udelay(arb->slew_delay_us);
	53
	54	/* Wait for the other master to release it */
	55	stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
	56	while (time_before(jiffies, stop_retry)) {
d9a183bf	57	int gpio_val = gpiod_get_value(arb->their_gpio);
b81dfaa0	58
d9a183bf	59	if (!gpio_val) {
b81dfaa0 DA	60	/* We got it, so return */
	61	return 0;
	62	}
	63
	64	usleep_range(50, 200);
	65	}
	66
	67	/* It didn't release, so give up, wait, and try again */
d9a183bf	68	gpiod_set_value(arb->our_gpio, 0);
b81dfaa0 DA	69
	70	usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
	71	} while (time_before(jiffies, stop_time));
	72
	73	/* Give up, release our claim */
d9a183bf	74	gpiod_set_value(arb->our_gpio, 0);
b81dfaa0	75	udelay(arb->slew_delay_us);
8aacd901	76	dev_err(muxc->dev, "Could not claim bus, timeout\n");
b81dfaa0 DA	77	return -EBUSY;
	78	}
	79
45ce82f5	80	/*
b81dfaa0 DA	81	* i2c_arbitrator_deselect - release the I2C bus
	82	*
	83	* Release the I2C bus using the GPIO-based signalling protocol.
	84	*/
8aacd901	85	static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
b81dfaa0	86	{
8aacd901	87	const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
b81dfaa0 DA	88
b81dfaa0 DA	89	/* Release the bus and wait for the other master to notice */
d9a183bf	90	gpiod_set_value(arb->our_gpio, 0);
b81dfaa0 DA	91	udelay(arb->slew_delay_us);
	92
	93	return 0;
	94	}
	95
	96	static int i2c_arbitrator_probe(struct platform_device *pdev)
	97	{
	98	struct device *dev = &pdev->dev;
	99	struct device_node *np = dev->of_node;
	100	struct device_node *parent_np;
8aacd901	101	struct i2c_mux_core *muxc;
b81dfaa0	102	struct i2c_arbitrator_data *arb;
d9a183bf	103	struct gpio_desc *dummy;
b81dfaa0 DA	104	int ret;
	105
	106	/* We only support probing from device tree; no platform_data */
	107	if (!np) {
	108	dev_err(dev, "Cannot find device tree node\n");
	109	return -ENODEV;
	110	}
6d4028c6	111	if (dev_get_platdata(dev)) {
b81dfaa0 DA	112	dev_err(dev, "Platform data is not supported\n");
	113	return -EINVAL;
	114	}
	115
40839590	116	muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
8aacd901 PR	117	i2c_arbitrator_select, i2c_arbitrator_deselect);
8aacd901 PR	118	if (!muxc)
b81dfaa0	119	return -ENOMEM;
8aacd901 PR	120	arb = i2c_mux_priv(muxc);
	121
	122	platform_set_drvdata(pdev, muxc);
b81dfaa0	123
d9a183bf LW	124	/* Request GPIOs, our GPIO as unclaimed to begin with */
	125	arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);
	126	if (IS_ERR(arb->our_gpio)) {
	127	dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",
	128	PTR_ERR(arb->our_gpio));
	129	return PTR_ERR(arb->our_gpio);
b81dfaa0 DA	130	}
b81dfaa0 DA	131
d9a183bf LW	132	arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);
	133	if (IS_ERR(arb->their_gpio)) {
	134	dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",
	135	PTR_ERR(arb->their_gpio));
	136	return PTR_ERR(arb->their_gpio);
b81dfaa0 DA	137	}
	138
	139	/* At the moment we only support a single two master (us + 1 other) */
d9a183bf LW	140	dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);
d9a183bf LW	141	if (!IS_ERR(dummy)) {
b81dfaa0 DA	142	dev_err(dev, "Only one other master is supported\n");
b81dfaa0 DA	143	return -EINVAL;
d9a183bf LW	144	} else if (PTR_ERR(dummy) == -EPROBE_DEFER) {
d9a183bf LW	145	return -EPROBE_DEFER;
b81dfaa0 DA	146	}
	147
	148	/* Arbitration parameters */
	149	if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
	150	arb->slew_delay_us = 10;
	151	if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
	152	arb->wait_retry_us = 3000;
	153	if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
	154	arb->wait_free_us = 50000;
	155
	156	/* Find our parent */
	157	parent_np = of_parse_phandle(np, "i2c-parent", 0);
	158	if (!parent_np) {
	159	dev_err(dev, "Cannot parse i2c-parent\n");
	160	return -EINVAL;
	161	}
8aacd901	162	muxc->parent = of_get_i2c_adapter_by_node(parent_np);
bdbf4a29	163	of_node_put(parent_np);
8aacd901	164	if (!muxc->parent) {
b81dfaa0	165	dev_err(dev, "Cannot find parent bus\n");
0cd98069	166	return -EPROBE_DEFER;
b81dfaa0 DA	167	}
	168
	169	/* Actually add the mux adapter */
8aacd901	170	ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
1144d13e	171	if (ret)
8aacd901	172	i2c_put_adapter(muxc->parent);
b81dfaa0 DA	173
	174	return ret;
	175	}
	176
	177	static int i2c_arbitrator_remove(struct platform_device *pdev)
	178	{
8aacd901	179	struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
b81dfaa0	180
8aacd901 PR	181	i2c_mux_del_adapters(muxc);
8aacd901 PR	182	i2c_put_adapter(muxc->parent);
b81dfaa0 DA	183	return 0;
	184	}
	185
	186	static const struct of_device_id i2c_arbitrator_of_match[] = {
	187	{ .compatible = "i2c-arb-gpio-challenge", },
	188	{},
	189	};
	190	MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
	191
	192	static struct platform_driver i2c_arbitrator_driver = {
	193	.probe = i2c_arbitrator_probe,
	194	.remove = i2c_arbitrator_remove,
	195	.driver = {
b81dfaa0	196	.name = "i2c-arb-gpio-challenge",
4e905323	197	.of_match_table = i2c_arbitrator_of_match,
b81dfaa0 DA	198	},
	199	};
	200
	201	module_platform_driver(i2c_arbitrator_driver);
	202
	203	MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
	204	MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
	205	MODULE_LICENSE("GPL v2");
	206	MODULE_ALIAS("platform:i2c-arb-gpio-challenge");