/*
 * 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_find_i2c_adapter_by_node(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 = {
                .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");