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// SPDX-License-Identifier: GPL-2.0-only
/*
* GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
*
* Copyright (C) 2012 Google, Inc
*/
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/kernel.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
/**
* struct i2c_arbitrator_data - Driver data for I2C arbitrator
*
* @our_gpio: GPIO descriptor we'll use to claim.
* @their_gpio: GPIO descriptor that the other side will use to claim.
* @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 gpio_desc *our_gpio;
struct gpio_desc *their_gpio;
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_mux_core *muxc, u32 chan)
{
const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
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 */
gpiod_set_value(arb->our_gpio, 1);
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 = gpiod_get_value(arb->their_gpio);
if (!gpio_val) {
/* We got it, so return */
return 0;
}
usleep_range(50, 200);
}
/* It didn't release, so give up, wait, and try again */
gpiod_set_value(arb->our_gpio, 0);
usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
} while (time_before(jiffies, stop_time));
/* Give up, release our claim */
gpiod_set_value(arb->our_gpio, 0);
udelay(arb->slew_delay_us);
dev_err(muxc->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_mux_core *muxc, u32 chan)
{
const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
/* Release the bus and wait for the other master to notice */
gpiod_set_value(arb->our_gpio, 0);
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_mux_core *muxc;
struct i2c_arbitrator_data *arb;
struct gpio_desc *dummy;
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;
}
muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
i2c_arbitrator_select, i2c_arbitrator_deselect);
if (!muxc)
return -ENOMEM;
arb = i2c_mux_priv(muxc);
platform_set_drvdata(pdev, muxc);
/* Request GPIOs, our GPIO as unclaimed to begin with */
arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);
if (IS_ERR(arb->our_gpio)) {
dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",
PTR_ERR(arb->our_gpio));
return PTR_ERR(arb->our_gpio);
}
arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);
if (IS_ERR(arb->their_gpio)) {
dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",
PTR_ERR(arb->their_gpio));
return PTR_ERR(arb->their_gpio);
}
/* At the moment we only support a single two master (us + 1 other) */
dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);
if (!IS_ERR(dummy)) {
dev_err(dev, "Only one other master is supported\n");
return -EINVAL;
} else if (PTR_ERR(dummy) == -EPROBE_DEFER) {
return -EPROBE_DEFER;
}
/* 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;
}
muxc->parent = of_get_i2c_adapter_by_node(parent_np);
of_node_put(parent_np);
if (!muxc->parent) {
dev_err(dev, "Cannot find parent bus\n");
return -EPROBE_DEFER;
}
/* Actually add the mux adapter */
ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
if (ret)
i2c_put_adapter(muxc->parent);
return ret;
}
static int i2c_arbitrator_remove(struct platform_device *pdev)
{
struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
i2c_mux_del_adapters(muxc);
i2c_put_adapter(muxc->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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