![Wolfram Sang](/assets/img/avatar_default.png)
I2C of helpers used to live in of_i2c.c but experience (from SPI) shows that it is much cleaner to have this in the core. This also removes a circular dependency between the helpers and the core, and so we can finally register child nodes in the core instead of doing this manually in each driver. So, fix the drivers and documentation, too. Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
251 lines
7.1 KiB
C
251 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/init.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_find_i2c_adapter_by_node(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 -EINVAL;
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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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.owner = THIS_MODULE,
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.name = "i2c-arb-gpio-challenge",
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.of_match_table = of_match_ptr(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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