drivers/i2c/muxes/i2c-arb-gpio-challenge.c - arm/linux - Git at Google

 /*
  * 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
  *
  * @parent: Parent adapter
  * @child: Child bus
  * @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 {
 	struct i2c_adapter *parent;
 	struct i2c_adapter *child;
 	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_adapter *adap, void *data, u32 chan)
 {
 	const struct i2c_arbitrator_data *arb = data;
 	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(&adap->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_adapter *adap, void *data,
 				   u32 chan)
 {
 	const struct i2c_arbitrator_data *arb = data;

 	/* 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_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;
 	}

 	arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
 	if (!arb) {
 		dev_err(dev, "Cannot allocate i2c_arbitrator_data\n");
 		return -ENOMEM;
 	}
 	platform_set_drvdata(pdev, arb);

 	/* 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;
 	}
 	arb->parent = of_get_i2c_adapter_by_node(parent_np);
 	of_node_put(parent_np);
 	if (!arb->parent) {
 		dev_err(dev, "Cannot find parent bus\n");
 		return -EPROBE_DEFER;
 	}

 	/* Actually add the mux adapter */
 	arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0,
 					 i2c_arbitrator_select,
 					 i2c_arbitrator_deselect);
 	if (!arb->child) {
 		dev_err(dev, "Failed to add adapter\n");
 		ret = -ENODEV;
 		i2c_put_adapter(arb->parent);
 	}

 	return ret;
 }

 static int i2c_arbitrator_remove(struct platform_device *pdev)
 {
 	struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev);

 	i2c_del_mux_adapter(arb->child);
 	i2c_put_adapter(arb->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");
	/*
	* 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
	*
	* @parent: Parent adapter
	* @child: Child bus
	* @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 {
	struct i2c_adapter *parent;
	struct i2c_adapter *child;
	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_adapter adap, void data, u32 chan)
	{
	const struct i2c_arbitrator_data *arb = data;
	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(&adap->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_adapter adap, void data,
	u32 chan)
	{
	const struct i2c_arbitrator_data *arb = data;

	/* 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_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;
	}

	arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
	if (!arb) {
	dev_err(dev, "Cannot allocate i2c_arbitrator_data\n");
	return -ENOMEM;
	}
	platform_set_drvdata(pdev, arb);

	/* 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;
	}
	arb->parent = of_get_i2c_adapter_by_node(parent_np);
	of_node_put(parent_np);
	if (!arb->parent) {
	dev_err(dev, "Cannot find parent bus\n");
	return -EPROBE_DEFER;
	}

	/* Actually add the mux adapter */
	arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0,
	i2c_arbitrator_select,
	i2c_arbitrator_deselect);
	if (!arb->child) {
	dev_err(dev, "Failed to add adapter\n");
	ret = -ENODEV;
	i2c_put_adapter(arb->parent);
	}

	return ret;
	}

	static int i2c_arbitrator_remove(struct platform_device *pdev)
	{
	struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev);

	i2c_del_mux_adapter(arb->child);
	i2c_put_adapter(arb->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");