summaryrefslogtreecommitdiff
path: root/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
blob: 5cf1b60b69e2140e674c7245577971c12c3e65b5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
/*
 * 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_find_i2c_adapter_by_node(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");