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

/*
 * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
 *
 * Copyright (C) 2012 Google, Inc
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

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


/**
 * struct i2c_arbitrator_data - Driver data for I2C arbitrator
 *
 * @our_gpio: GPIO we'll use to claim.
 * @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
 *   this then consider it released.
 * @their_gpio: GPIO that the other side will use to claim.
 * @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
 *   this then consider it released.
 * @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 {
	int our_gpio;
	int our_gpio_release;
	int their_gpio;
	int their_gpio_release;
	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 */
		gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
		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 = !!gpio_get_value(arb->their_gpio);

			if (gpio_val == arb->their_gpio_release) {
				/* We got it, so return */
				return 0;
			}

			usleep_range(50, 200);
		}

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

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

	/* Give up, release our claim */
	gpio_set_value(arb->our_gpio, arb->our_gpio_release);
	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 */
	gpio_set_value(arb->our_gpio, arb->our_gpio_release);
	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;
	enum of_gpio_flags gpio_flags;
	unsigned long out_init;
	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 */
	ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
	if (!gpio_is_valid(ret)) {
		if (ret != -EPROBE_DEFER)
			dev_err(dev, "Error getting our-claim-gpio\n");
		return ret;
	}
	arb->our_gpio = ret;
	arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
	out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
		GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
	ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
				    "our-claim-gpio");
	if (ret) {
		if (ret != -EPROBE_DEFER)
			dev_err(dev, "Error requesting our-claim-gpio\n");
		return ret;
	}

	ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
	if (!gpio_is_valid(ret)) {
		if (ret != -EPROBE_DEFER)
			dev_err(dev, "Error getting their-claim-gpio\n");
		return ret;
	}
	arb->their_gpio = ret;
	arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
	ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
				    "their-claim-gpio");
	if (ret) {
		if (ret != -EPROBE_DEFER)
			dev_err(dev, "Error requesting their-claim-gpio\n");
		return ret;
	}

	/* At the moment we only support a single two master (us + 1 other) */
	if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
		dev_err(dev, "Only one other master is supported\n");
		return -EINVAL;
	}

	/* 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) {
		dev_err(dev, "Failed to add adapter\n");
		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
b81dfaa0 DA	1	/*
	2	* GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
	3	*
	4	* Copyright (C) 2012 Google, Inc
	5	*
	6	* This software is licensed under the terms of the GNU General Public
	7	* License version 2, as published by the Free Software Foundation, and
	8	* may be copied, distributed, and modified under those terms.
	9	*
	10	* This program is distributed in the hope that it will be useful,
	11	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	13	* GNU General Public License for more details.
	14	*
	15	*/
	16
	17	#include <linux/delay.h>
	18	#include <linux/gpio.h>
	19	#include <linux/kernel.h>
	20	#include <linux/i2c.h>
	21	#include <linux/i2c-mux.h>
b81dfaa0	22	#include <linux/module.h>
b81dfaa0 DA	23	#include <linux/of_gpio.h>
	24	#include <linux/platform_device.h>
	25	#include <linux/slab.h>
	26
	27
	28	/**
	29	* struct i2c_arbitrator_data - Driver data for I2C arbitrator
	30	*
b81dfaa0 DA	31	* @our_gpio: GPIO we'll use to claim.
	32	* @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
	33	* this then consider it released.
	34	* @their_gpio: GPIO that the other side will use to claim.
	35	* @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
	36	* this then consider it released.
	37	* @slew_delay_us: microseconds to wait for a GPIO to go high.
	38	* @wait_retry_us: we'll attempt another claim after this many microseconds.
	39	* @wait_free_us: we'll give up after this many microseconds.
	40	*/
	41
	42	struct i2c_arbitrator_data {
b81dfaa0 DA	43	int our_gpio;
	44	int our_gpio_release;
	45	int their_gpio;
	46	int their_gpio_release;
	47	unsigned int slew_delay_us;
	48	unsigned int wait_retry_us;
	49	unsigned int wait_free_us;
	50	};
	51
	52
	53	/**
	54	* i2c_arbitrator_select - claim the I2C bus
	55	*
	56	* Use the GPIO-based signalling protocol; return -EBUSY if we fail.
	57	*/
8aacd901	58	static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
b81dfaa0	59	{
8aacd901	60	const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
b81dfaa0 DA	61	unsigned long stop_retry, stop_time;
	62
	63	/* Start a round of trying to claim the bus */
	64	stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
	65	do {
	66	/* Indicate that we want to claim the bus */
	67	gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
	68	udelay(arb->slew_delay_us);
	69
	70	/* Wait for the other master to release it */
	71	stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
	72	while (time_before(jiffies, stop_retry)) {
	73	int gpio_val = !!gpio_get_value(arb->their_gpio);
	74
	75	if (gpio_val == arb->their_gpio_release) {
	76	/* We got it, so return */
	77	return 0;
	78	}
	79
	80	usleep_range(50, 200);
	81	}
	82
	83	/* It didn't release, so give up, wait, and try again */
	84	gpio_set_value(arb->our_gpio, arb->our_gpio_release);
	85
	86	usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
	87	} while (time_before(jiffies, stop_time));
	88
	89	/* Give up, release our claim */
	90	gpio_set_value(arb->our_gpio, arb->our_gpio_release);
	91	udelay(arb->slew_delay_us);
8aacd901	92	dev_err(muxc->dev, "Could not claim bus, timeout\n");
b81dfaa0 DA	93	return -EBUSY;
	94	}
	95
	96	/**
	97	* i2c_arbitrator_deselect - release the I2C bus
	98	*
	99	* Release the I2C bus using the GPIO-based signalling protocol.
	100	*/
8aacd901	101	static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
b81dfaa0	102	{
8aacd901	103	const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
b81dfaa0 DA	104
	105	/* Release the bus and wait for the other master to notice */
	106	gpio_set_value(arb->our_gpio, arb->our_gpio_release);
	107	udelay(arb->slew_delay_us);
	108
	109	return 0;
	110	}
	111
	112	static int i2c_arbitrator_probe(struct platform_device *pdev)
	113	{
	114	struct device *dev = &pdev->dev;
	115	struct device_node *np = dev->of_node;
	116	struct device_node *parent_np;
8aacd901	117	struct i2c_mux_core *muxc;
b81dfaa0 DA	118	struct i2c_arbitrator_data *arb;
	119	enum of_gpio_flags gpio_flags;
	120	unsigned long out_init;
	121	int ret;
	122
	123	/* We only support probing from device tree; no platform_data */
	124	if (!np) {
	125	dev_err(dev, "Cannot find device tree node\n");
	126	return -ENODEV;
	127	}
6d4028c6	128	if (dev_get_platdata(dev)) {
b81dfaa0 DA	129	dev_err(dev, "Platform data is not supported\n");
	130	return -EINVAL;
	131	}
	132
40839590	133	muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
8aacd901 PR	134	i2c_arbitrator_select, i2c_arbitrator_deselect);
8aacd901 PR	135	if (!muxc)
b81dfaa0	136	return -ENOMEM;
8aacd901 PR	137	arb = i2c_mux_priv(muxc);
	138
	139	platform_set_drvdata(pdev, muxc);
b81dfaa0 DA	140
	141	/* Request GPIOs */
	142	ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
	143	if (!gpio_is_valid(ret)) {
	144	if (ret != -EPROBE_DEFER)
	145	dev_err(dev, "Error getting our-claim-gpio\n");
	146	return ret;
	147	}
	148	arb->our_gpio = ret;
	149	arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
	150	out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
	151	GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
	152	ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
	153	"our-claim-gpio");
	154	if (ret) {
	155	if (ret != -EPROBE_DEFER)
	156	dev_err(dev, "Error requesting our-claim-gpio\n");
	157	return ret;
	158	}
	159
	160	ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
	161	if (!gpio_is_valid(ret)) {
	162	if (ret != -EPROBE_DEFER)
	163	dev_err(dev, "Error getting their-claim-gpio\n");
	164	return ret;
	165	}
	166	arb->their_gpio = ret;
	167	arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
	168	ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
	169	"their-claim-gpio");
	170	if (ret) {
	171	if (ret != -EPROBE_DEFER)
	172	dev_err(dev, "Error requesting their-claim-gpio\n");
	173	return ret;
	174	}
	175
	176	/* At the moment we only support a single two master (us + 1 other) */
	177	if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
	178	dev_err(dev, "Only one other master is supported\n");
	179	return -EINVAL;
	180	}
	181
	182	/* Arbitration parameters */
	183	if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
	184	arb->slew_delay_us = 10;
	185	if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
	186	arb->wait_retry_us = 3000;
	187	if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
	188	arb->wait_free_us = 50000;
	189
	190	/* Find our parent */
	191	parent_np = of_parse_phandle(np, "i2c-parent", 0);
	192	if (!parent_np) {
	193	dev_err(dev, "Cannot parse i2c-parent\n");
	194	return -EINVAL;
	195	}
8aacd901	196	muxc->parent = of_get_i2c_adapter_by_node(parent_np);
bdbf4a29	197	of_node_put(parent_np);
8aacd901	198	if (!muxc->parent) {
b81dfaa0	199	dev_err(dev, "Cannot find parent bus\n");
0cd98069	200	return -EPROBE_DEFER;
b81dfaa0 DA	201	}
	202
	203	/* Actually add the mux adapter */
8aacd901 PR	204	ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
8aacd901 PR	205	if (ret) {
b81dfaa0	206	dev_err(dev, "Failed to add adapter\n");
8aacd901	207	i2c_put_adapter(muxc->parent);
b81dfaa0 DA	208	}
	209
	210	return ret;
	211	}
	212
	213	static int i2c_arbitrator_remove(struct platform_device *pdev)
	214	{
8aacd901	215	struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
b81dfaa0	216
8aacd901 PR	217	i2c_mux_del_adapters(muxc);
8aacd901 PR	218	i2c_put_adapter(muxc->parent);
b81dfaa0 DA	219	return 0;
	220	}
	221
	222	static const struct of_device_id i2c_arbitrator_of_match[] = {
	223	{ .compatible = "i2c-arb-gpio-challenge", },
	224	{},
	225	};
	226	MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
	227
	228	static struct platform_driver i2c_arbitrator_driver = {
	229	.probe = i2c_arbitrator_probe,
	230	.remove = i2c_arbitrator_remove,
	231	.driver = {
b81dfaa0	232	.name = "i2c-arb-gpio-challenge",
4e905323	233	.of_match_table = i2c_arbitrator_of_match,
b81dfaa0 DA	234	},
	235	};
	236
	237	module_platform_driver(i2c_arbitrator_driver);
	238
	239	MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
	240	MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
	241	MODULE_LICENSE("GPL v2");
	242	MODULE_ALIAS("platform:i2c-arb-gpio-challenge");