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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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