250 lines
7.1 KiB
C
250 lines
7.1 KiB
C
/*
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* GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
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*
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* Copyright (C) 2012 Google, Inc
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*
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* This software is licensed under the terms of the GNU General Public
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* License version 2, as published by the Free Software Foundation, and
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* may be copied, distributed, and modified under those terms.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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*/
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#include <linux/delay.h>
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#include <linux/gpio.h>
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#include <linux/kernel.h>
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#include <linux/i2c.h>
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#include <linux/i2c-mux.h>
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#include <linux/module.h>
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#include <linux/of_gpio.h>
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#include <linux/platform_device.h>
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#include <linux/slab.h>
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/**
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* struct i2c_arbitrator_data - Driver data for I2C arbitrator
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*
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* @parent: Parent adapter
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* @child: Child bus
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* @our_gpio: GPIO we'll use to claim.
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* @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
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* this then consider it released.
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* @their_gpio: GPIO that the other side will use to claim.
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* @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
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* this then consider it released.
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* @slew_delay_us: microseconds to wait for a GPIO to go high.
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* @wait_retry_us: we'll attempt another claim after this many microseconds.
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* @wait_free_us: we'll give up after this many microseconds.
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*/
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struct i2c_arbitrator_data {
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struct i2c_adapter *parent;
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struct i2c_adapter *child;
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int our_gpio;
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int our_gpio_release;
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int their_gpio;
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int their_gpio_release;
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unsigned int slew_delay_us;
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unsigned int wait_retry_us;
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unsigned int wait_free_us;
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};
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/**
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* i2c_arbitrator_select - claim the I2C bus
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*
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* Use the GPIO-based signalling protocol; return -EBUSY if we fail.
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*/
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static int i2c_arbitrator_select(struct i2c_adapter *adap, void *data, u32 chan)
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{
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const struct i2c_arbitrator_data *arb = data;
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unsigned long stop_retry, stop_time;
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/* Start a round of trying to claim the bus */
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stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
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do {
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/* Indicate that we want to claim the bus */
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gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
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udelay(arb->slew_delay_us);
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/* Wait for the other master to release it */
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stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
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while (time_before(jiffies, stop_retry)) {
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int gpio_val = !!gpio_get_value(arb->their_gpio);
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if (gpio_val == arb->their_gpio_release) {
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/* We got it, so return */
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return 0;
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}
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usleep_range(50, 200);
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}
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/* It didn't release, so give up, wait, and try again */
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gpio_set_value(arb->our_gpio, arb->our_gpio_release);
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usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
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} while (time_before(jiffies, stop_time));
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/* Give up, release our claim */
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gpio_set_value(arb->our_gpio, arb->our_gpio_release);
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udelay(arb->slew_delay_us);
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dev_err(&adap->dev, "Could not claim bus, timeout\n");
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return -EBUSY;
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}
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/**
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* i2c_arbitrator_deselect - release the I2C bus
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*
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* Release the I2C bus using the GPIO-based signalling protocol.
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*/
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static int i2c_arbitrator_deselect(struct i2c_adapter *adap, void *data,
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u32 chan)
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{
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const struct i2c_arbitrator_data *arb = data;
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/* Release the bus and wait for the other master to notice */
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gpio_set_value(arb->our_gpio, arb->our_gpio_release);
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udelay(arb->slew_delay_us);
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return 0;
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}
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static int i2c_arbitrator_probe(struct platform_device *pdev)
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{
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struct device *dev = &pdev->dev;
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struct device_node *np = dev->of_node;
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struct device_node *parent_np;
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struct i2c_arbitrator_data *arb;
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enum of_gpio_flags gpio_flags;
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unsigned long out_init;
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int ret;
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/* We only support probing from device tree; no platform_data */
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if (!np) {
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dev_err(dev, "Cannot find device tree node\n");
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return -ENODEV;
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}
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if (dev_get_platdata(dev)) {
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dev_err(dev, "Platform data is not supported\n");
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return -EINVAL;
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}
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arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
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if (!arb) {
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dev_err(dev, "Cannot allocate i2c_arbitrator_data\n");
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return -ENOMEM;
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}
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platform_set_drvdata(pdev, arb);
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/* Request GPIOs */
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ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
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if (!gpio_is_valid(ret)) {
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if (ret != -EPROBE_DEFER)
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dev_err(dev, "Error getting our-claim-gpio\n");
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return ret;
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}
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arb->our_gpio = ret;
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arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
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out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
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GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
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ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
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"our-claim-gpio");
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if (ret) {
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if (ret != -EPROBE_DEFER)
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dev_err(dev, "Error requesting our-claim-gpio\n");
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return ret;
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}
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ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
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if (!gpio_is_valid(ret)) {
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if (ret != -EPROBE_DEFER)
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dev_err(dev, "Error getting their-claim-gpio\n");
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return ret;
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}
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arb->their_gpio = ret;
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arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
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ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
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"their-claim-gpio");
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if (ret) {
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if (ret != -EPROBE_DEFER)
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dev_err(dev, "Error requesting their-claim-gpio\n");
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return ret;
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}
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/* At the moment we only support a single two master (us + 1 other) */
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if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
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dev_err(dev, "Only one other master is supported\n");
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return -EINVAL;
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}
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/* Arbitration parameters */
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if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
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arb->slew_delay_us = 10;
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if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
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arb->wait_retry_us = 3000;
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if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
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arb->wait_free_us = 50000;
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/* Find our parent */
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parent_np = of_parse_phandle(np, "i2c-parent", 0);
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if (!parent_np) {
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dev_err(dev, "Cannot parse i2c-parent\n");
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return -EINVAL;
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}
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arb->parent = of_get_i2c_adapter_by_node(parent_np);
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of_node_put(parent_np);
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if (!arb->parent) {
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dev_err(dev, "Cannot find parent bus\n");
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return -EPROBE_DEFER;
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}
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/* Actually add the mux adapter */
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arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0,
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i2c_arbitrator_select,
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i2c_arbitrator_deselect);
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if (!arb->child) {
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dev_err(dev, "Failed to add adapter\n");
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ret = -ENODEV;
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i2c_put_adapter(arb->parent);
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}
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return ret;
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}
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static int i2c_arbitrator_remove(struct platform_device *pdev)
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{
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struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev);
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i2c_del_mux_adapter(arb->child);
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i2c_put_adapter(arb->parent);
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return 0;
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}
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static const struct of_device_id i2c_arbitrator_of_match[] = {
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{ .compatible = "i2c-arb-gpio-challenge", },
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{},
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};
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MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
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static struct platform_driver i2c_arbitrator_driver = {
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.probe = i2c_arbitrator_probe,
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.remove = i2c_arbitrator_remove,
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.driver = {
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.name = "i2c-arb-gpio-challenge",
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.of_match_table = i2c_arbitrator_of_match,
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},
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};
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module_platform_driver(i2c_arbitrator_driver);
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MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
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MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
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MODULE_LICENSE("GPL v2");
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MODULE_ALIAS("platform:i2c-arb-gpio-challenge");
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