/*
   * 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
  ");
  	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
  ");
  		return -ENODEV;
  	}
  	if (dev_get_platdata(dev)) {
  		dev_err(dev, "Platform data is not supported
  ");
  		return -EINVAL;
  	}
  
  	arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
  	if (!arb) {
  		dev_err(dev, "Cannot allocate i2c_arbitrator_data
  ");
  		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
  ");
  		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
  ");
  		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
  ");
  		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
  ");
  		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
  ");
  		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
  ");
  		return -EINVAL;
  	}
  	arb->parent = of_find_i2c_adapter_by_node(parent_np);
  	if (!arb->parent) {
  		dev_err(dev, "Cannot find parent bus
  ");
  		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
  ");
  		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	= {
  		.owner	= THIS_MODULE,
  		.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");