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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
4 *
5 * Copyright (C) 2012 Google, Inc
6 */
7
8#include <linux/delay.h>
9#include <linux/gpio/consumer.h>
10#include <linux/kernel.h>
11#include <linux/i2c.h>
12#include <linux/i2c-mux.h>
13#include <linux/module.h>
14#include <linux/platform_device.h>
15#include <linux/slab.h>
16
17
18/**
19 * struct i2c_arbitrator_data - Driver data for I2C arbitrator
20 *
21 * @our_gpio: GPIO descriptor we'll use to claim.
22 * @their_gpio: GPIO descriptor that the other side will use to claim.
23 * @slew_delay_us: microseconds to wait for a GPIO to go high.
24 * @wait_retry_us: we'll attempt another claim after this many microseconds.
25 * @wait_free_us: we'll give up after this many microseconds.
26 */
27
28struct i2c_arbitrator_data {
29 struct gpio_desc *our_gpio;
30 struct gpio_desc *their_gpio;
31 unsigned int slew_delay_us;
32 unsigned int wait_retry_us;
33 unsigned int wait_free_us;
34};
35
36
37/**
38 * i2c_arbitrator_select - claim the I2C bus
39 *
40 * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
41 */
42static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
43{
44 const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
45 unsigned long stop_retry, stop_time;
46
47 /* Start a round of trying to claim the bus */
48 stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
49 do {
50 /* Indicate that we want to claim the bus */
51 gpiod_set_value(arb->our_gpio, 1);
52 udelay(arb->slew_delay_us);
53
54 /* Wait for the other master to release it */
55 stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
56 while (time_before(jiffies, stop_retry)) {
57 int gpio_val = gpiod_get_value(arb->their_gpio);
58
59 if (!gpio_val) {
60 /* We got it, so return */
61 return 0;
62 }
63
64 usleep_range(50, 200);
65 }
66
67 /* It didn't release, so give up, wait, and try again */
68 gpiod_set_value(arb->our_gpio, 0);
69
70 usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
71 } while (time_before(jiffies, stop_time));
72
73 /* Give up, release our claim */
74 gpiod_set_value(arb->our_gpio, 0);
75 udelay(arb->slew_delay_us);
76 dev_err(muxc->dev, "Could not claim bus, timeout\n");
77 return -EBUSY;
78}
79
80/**
81 * i2c_arbitrator_deselect - release the I2C bus
82 *
83 * Release the I2C bus using the GPIO-based signalling protocol.
84 */
85static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
86{
87 const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
88
89 /* Release the bus and wait for the other master to notice */
90 gpiod_set_value(arb->our_gpio, 0);
91 udelay(arb->slew_delay_us);
92
93 return 0;
94}
95
96static int i2c_arbitrator_probe(struct platform_device *pdev)
97{
98 struct device *dev = &pdev->dev;
99 struct device_node *np = dev->of_node;
100 struct device_node *parent_np;
101 struct i2c_mux_core *muxc;
102 struct i2c_arbitrator_data *arb;
103 struct gpio_desc *dummy;
104 int ret;
105
106 /* We only support probing from device tree; no platform_data */
107 if (!np) {
108 dev_err(dev, "Cannot find device tree node\n");
109 return -ENODEV;
110 }
111 if (dev_get_platdata(dev)) {
112 dev_err(dev, "Platform data is not supported\n");
113 return -EINVAL;
114 }
115
116 muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
117 i2c_arbitrator_select, i2c_arbitrator_deselect);
118 if (!muxc)
119 return -ENOMEM;
120 arb = i2c_mux_priv(muxc);
121
122 platform_set_drvdata(pdev, muxc);
123
124 /* Request GPIOs, our GPIO as unclaimed to begin with */
125 arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);
126 if (IS_ERR(arb->our_gpio)) {
127 dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",
128 PTR_ERR(arb->our_gpio));
129 return PTR_ERR(arb->our_gpio);
130 }
131
132 arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);
133 if (IS_ERR(arb->their_gpio)) {
134 dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",
135 PTR_ERR(arb->their_gpio));
136 return PTR_ERR(arb->their_gpio);
137 }
138
139 /* At the moment we only support a single two master (us + 1 other) */
140 dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);
141 if (!IS_ERR(dummy)) {
142 dev_err(dev, "Only one other master is supported\n");
143 return -EINVAL;
144 } else if (PTR_ERR(dummy) == -EPROBE_DEFER) {
145 return -EPROBE_DEFER;
146 }
147
148 /* Arbitration parameters */
149 if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
150 arb->slew_delay_us = 10;
151 if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
152 arb->wait_retry_us = 3000;
153 if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
154 arb->wait_free_us = 50000;
155
156 /* Find our parent */
157 parent_np = of_parse_phandle(np, "i2c-parent", 0);
158 if (!parent_np) {
159 dev_err(dev, "Cannot parse i2c-parent\n");
160 return -EINVAL;
161 }
162 muxc->parent = of_get_i2c_adapter_by_node(parent_np);
163 of_node_put(parent_np);
164 if (!muxc->parent) {
165 dev_err(dev, "Cannot find parent bus\n");
166 return -EPROBE_DEFER;
167 }
168
169 /* Actually add the mux adapter */
170 ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
171 if (ret)
172 i2c_put_adapter(muxc->parent);
173
174 return ret;
175}
176
177static int i2c_arbitrator_remove(struct platform_device *pdev)
178{
179 struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
180
181 i2c_mux_del_adapters(muxc);
182 i2c_put_adapter(muxc->parent);
183 return 0;
184}
185
186static const struct of_device_id i2c_arbitrator_of_match[] = {
187 { .compatible = "i2c-arb-gpio-challenge", },
188 {},
189};
190MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
191
192static struct platform_driver i2c_arbitrator_driver = {
193 .probe = i2c_arbitrator_probe,
194 .remove = i2c_arbitrator_remove,
195 .driver = {
196 .name = "i2c-arb-gpio-challenge",
197 .of_match_table = i2c_arbitrator_of_match,
198 },
199};
200
201module_platform_driver(i2c_arbitrator_driver);
202
203MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
204MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
205MODULE_LICENSE("GPL v2");
206MODULE_ALIAS("platform:i2c-arb-gpio-challenge");
1/*
2 * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
3 *
4 * Copyright (C) 2012 Google, Inc
5 *
6 * This software is licensed under the terms of the GNU General Public
7 * License version 2, as published by the Free Software Foundation, and
8 * may be copied, distributed, and modified under those terms.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 */
16
17#include <linux/delay.h>
18#include <linux/gpio.h>
19#include <linux/kernel.h>
20#include <linux/i2c.h>
21#include <linux/i2c-mux.h>
22#include <linux/module.h>
23#include <linux/of_gpio.h>
24#include <linux/platform_device.h>
25#include <linux/slab.h>
26
27
28/**
29 * struct i2c_arbitrator_data - Driver data for I2C arbitrator
30 *
31 * @our_gpio: GPIO we'll use to claim.
32 * @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
33 * this then consider it released.
34 * @their_gpio: GPIO that the other side will use to claim.
35 * @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
36 * this then consider it released.
37 * @slew_delay_us: microseconds to wait for a GPIO to go high.
38 * @wait_retry_us: we'll attempt another claim after this many microseconds.
39 * @wait_free_us: we'll give up after this many microseconds.
40 */
41
42struct i2c_arbitrator_data {
43 int our_gpio;
44 int our_gpio_release;
45 int their_gpio;
46 int their_gpio_release;
47 unsigned int slew_delay_us;
48 unsigned int wait_retry_us;
49 unsigned int wait_free_us;
50};
51
52
53/**
54 * i2c_arbitrator_select - claim the I2C bus
55 *
56 * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
57 */
58static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
59{
60 const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
61 unsigned long stop_retry, stop_time;
62
63 /* Start a round of trying to claim the bus */
64 stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
65 do {
66 /* Indicate that we want to claim the bus */
67 gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
68 udelay(arb->slew_delay_us);
69
70 /* Wait for the other master to release it */
71 stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
72 while (time_before(jiffies, stop_retry)) {
73 int gpio_val = !!gpio_get_value(arb->their_gpio);
74
75 if (gpio_val == arb->their_gpio_release) {
76 /* We got it, so return */
77 return 0;
78 }
79
80 usleep_range(50, 200);
81 }
82
83 /* It didn't release, so give up, wait, and try again */
84 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
85
86 usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
87 } while (time_before(jiffies, stop_time));
88
89 /* Give up, release our claim */
90 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
91 udelay(arb->slew_delay_us);
92 dev_err(muxc->dev, "Could not claim bus, timeout\n");
93 return -EBUSY;
94}
95
96/**
97 * i2c_arbitrator_deselect - release the I2C bus
98 *
99 * Release the I2C bus using the GPIO-based signalling protocol.
100 */
101static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
102{
103 const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
104
105 /* Release the bus and wait for the other master to notice */
106 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
107 udelay(arb->slew_delay_us);
108
109 return 0;
110}
111
112static int i2c_arbitrator_probe(struct platform_device *pdev)
113{
114 struct device *dev = &pdev->dev;
115 struct device_node *np = dev->of_node;
116 struct device_node *parent_np;
117 struct i2c_mux_core *muxc;
118 struct i2c_arbitrator_data *arb;
119 enum of_gpio_flags gpio_flags;
120 unsigned long out_init;
121 int ret;
122
123 /* We only support probing from device tree; no platform_data */
124 if (!np) {
125 dev_err(dev, "Cannot find device tree node\n");
126 return -ENODEV;
127 }
128 if (dev_get_platdata(dev)) {
129 dev_err(dev, "Platform data is not supported\n");
130 return -EINVAL;
131 }
132
133 muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
134 i2c_arbitrator_select, i2c_arbitrator_deselect);
135 if (!muxc)
136 return -ENOMEM;
137 arb = i2c_mux_priv(muxc);
138
139 platform_set_drvdata(pdev, muxc);
140
141 /* Request GPIOs */
142 ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
143 if (!gpio_is_valid(ret)) {
144 if (ret != -EPROBE_DEFER)
145 dev_err(dev, "Error getting our-claim-gpio\n");
146 return ret;
147 }
148 arb->our_gpio = ret;
149 arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
150 out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
151 GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
152 ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
153 "our-claim-gpio");
154 if (ret) {
155 if (ret != -EPROBE_DEFER)
156 dev_err(dev, "Error requesting our-claim-gpio\n");
157 return ret;
158 }
159
160 ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
161 if (!gpio_is_valid(ret)) {
162 if (ret != -EPROBE_DEFER)
163 dev_err(dev, "Error getting their-claim-gpio\n");
164 return ret;
165 }
166 arb->their_gpio = ret;
167 arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
168 ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
169 "their-claim-gpio");
170 if (ret) {
171 if (ret != -EPROBE_DEFER)
172 dev_err(dev, "Error requesting their-claim-gpio\n");
173 return ret;
174 }
175
176 /* At the moment we only support a single two master (us + 1 other) */
177 if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
178 dev_err(dev, "Only one other master is supported\n");
179 return -EINVAL;
180 }
181
182 /* Arbitration parameters */
183 if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
184 arb->slew_delay_us = 10;
185 if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
186 arb->wait_retry_us = 3000;
187 if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
188 arb->wait_free_us = 50000;
189
190 /* Find our parent */
191 parent_np = of_parse_phandle(np, "i2c-parent", 0);
192 if (!parent_np) {
193 dev_err(dev, "Cannot parse i2c-parent\n");
194 return -EINVAL;
195 }
196 muxc->parent = of_get_i2c_adapter_by_node(parent_np);
197 of_node_put(parent_np);
198 if (!muxc->parent) {
199 dev_err(dev, "Cannot find parent bus\n");
200 return -EPROBE_DEFER;
201 }
202
203 /* Actually add the mux adapter */
204 ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
205 if (ret)
206 i2c_put_adapter(muxc->parent);
207
208 return ret;
209}
210
211static int i2c_arbitrator_remove(struct platform_device *pdev)
212{
213 struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
214
215 i2c_mux_del_adapters(muxc);
216 i2c_put_adapter(muxc->parent);
217 return 0;
218}
219
220static const struct of_device_id i2c_arbitrator_of_match[] = {
221 { .compatible = "i2c-arb-gpio-challenge", },
222 {},
223};
224MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
225
226static struct platform_driver i2c_arbitrator_driver = {
227 .probe = i2c_arbitrator_probe,
228 .remove = i2c_arbitrator_remove,
229 .driver = {
230 .name = "i2c-arb-gpio-challenge",
231 .of_match_table = i2c_arbitrator_of_match,
232 },
233};
234
235module_platform_driver(i2c_arbitrator_driver);
236
237MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
238MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
239MODULE_LICENSE("GPL v2");
240MODULE_ALIAS("platform:i2c-arb-gpio-challenge");