1 // SPDX-License-Identifier: GPL-2.0-only
3  * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
12 #include <linux/i2c-mux.h>
19  * struct i2c_arbitrator_data - Driver data for I2C arbitrator
22  * @their_gpio: GPIO descriptor that the other side will use to claim.
38  * i2c_arbitrator_select - claim the I2C bus
40  * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
48 	stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;  in i2c_arbitrator_select()
51 		gpiod_set_value(arb->our_gpio, 1);  in i2c_arbitrator_select()
52 		udelay(arb->slew_delay_us);  in i2c_arbitrator_select()
54 		/* Wait for the other master to release it */  in i2c_arbitrator_select()
55 		stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;  in i2c_arbitrator_select()
57 			int gpio_val = gpiod_get_value(arb->their_gpio);  in i2c_arbitrator_select()
68 		gpiod_set_value(arb->our_gpio, 0);  in i2c_arbitrator_select()
70 		usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);  in i2c_arbitrator_select()
74 	gpiod_set_value(arb->our_gpio, 0);  in i2c_arbitrator_select()
75 	udelay(arb->slew_delay_us);  in i2c_arbitrator_select()
76 	dev_err(muxc->dev, "Could not claim bus, timeout\n");  in i2c_arbitrator_select()
77 	return -EBUSY;  in i2c_arbitrator_select()
81  * i2c_arbitrator_deselect - release the I2C bus
83  * Release the I2C bus using the GPIO-based signalling protocol.
89 	/* Release the bus and wait for the other master to notice */  in i2c_arbitrator_deselect()
90 	gpiod_set_value(arb->our_gpio, 0);  in i2c_arbitrator_deselect()
91 	udelay(arb->slew_delay_us);  in i2c_arbitrator_deselect()
98 	struct device *dev = &pdev->dev;  in i2c_arbitrator_probe()
99 	struct device_node *np = dev->of_node;  in i2c_arbitrator_probe()
109 		return -ENODEV;  in i2c_arbitrator_probe()
113 		return -EINVAL;  in i2c_arbitrator_probe()
119 		return -ENOMEM;  in i2c_arbitrator_probe()
125 	arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);  in i2c_arbitrator_probe()
126 	if (IS_ERR(arb->our_gpio)) {  in i2c_arbitrator_probe()
127 		dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",  in i2c_arbitrator_probe()
128 			PTR_ERR(arb->our_gpio));  in i2c_arbitrator_probe()
129 		return PTR_ERR(arb->our_gpio);  in i2c_arbitrator_probe()
132 	arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);  in i2c_arbitrator_probe()
133 	if (IS_ERR(arb->their_gpio)) {  in i2c_arbitrator_probe()
134 		dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",  in i2c_arbitrator_probe()
135 			PTR_ERR(arb->their_gpio));  in i2c_arbitrator_probe()
136 		return PTR_ERR(arb->their_gpio);  in i2c_arbitrator_probe()
139 	/* At the moment we only support a single two master (us + 1 other) */  in i2c_arbitrator_probe()
140 	dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);  in i2c_arbitrator_probe()
142 		dev_err(dev, "Only one other master is supported\n");  in i2c_arbitrator_probe()
143 		return -EINVAL;  in i2c_arbitrator_probe()
144 	} else if (PTR_ERR(dummy) == -EPROBE_DEFER) {  in i2c_arbitrator_probe()
145 		return -EPROBE_DEFER;  in i2c_arbitrator_probe()
149 	if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))  in i2c_arbitrator_probe()
150 		arb->slew_delay_us = 10;  in i2c_arbitrator_probe()
151 	if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))  in i2c_arbitrator_probe()
152 		arb->wait_retry_us = 3000;  in i2c_arbitrator_probe()
153 	if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))  in i2c_arbitrator_probe()
154 		arb->wait_free_us = 50000;  in i2c_arbitrator_probe()
157 	parent_np = of_parse_phandle(np, "i2c-parent", 0);  in i2c_arbitrator_probe()
159 		dev_err(dev, "Cannot parse i2c-parent\n");  in i2c_arbitrator_probe()
160 		return -EINVAL;  in i2c_arbitrator_probe()
162 	muxc->parent = of_get_i2c_adapter_by_node(parent_np);  in i2c_arbitrator_probe()
164 	if (!muxc->parent) {  in i2c_arbitrator_probe()
166 		return -EPROBE_DEFER;  in i2c_arbitrator_probe()
172 		i2c_put_adapter(muxc->parent);  in i2c_arbitrator_probe()
182 	i2c_put_adapter(muxc->parent);  in i2c_arbitrator_remove()
186 	{ .compatible = "i2c-arb-gpio-challenge", },
195 		.name	= "i2c-arb-gpio-challenge",
202 MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
205 MODULE_ALIAS("platform:i2c-arb-gpio-challenge");