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- /*
- * 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");
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