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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 * @parent: Parent adapter
32 * @child: Child bus
33 * @our_gpio: GPIO we'll use to claim.
34 * @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
35 * this then consider it released.
36 * @their_gpio: GPIO that the other side will use to claim.
37 * @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
38 * this then consider it released.
39 * @slew_delay_us: microseconds to wait for a GPIO to go high.
40 * @wait_retry_us: we'll attempt another claim after this many microseconds.
41 * @wait_free_us: we'll give up after this many microseconds.
42 */
43
44struct i2c_arbitrator_data {
45 struct i2c_adapter *parent;
46 struct i2c_adapter *child;
47 int our_gpio;
48 int our_gpio_release;
49 int their_gpio;
50 int their_gpio_release;
51 unsigned int slew_delay_us;
52 unsigned int wait_retry_us;
53 unsigned int wait_free_us;
54};
55
56
57/**
58 * i2c_arbitrator_select - claim the I2C bus
59 *
60 * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
61 */
62static int i2c_arbitrator_select(struct i2c_adapter *adap, void *data, u32 chan)
63{
64 const struct i2c_arbitrator_data *arb = data;
65 unsigned long stop_retry, stop_time;
66
67 /* Start a round of trying to claim the bus */
68 stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
69 do {
70 /* Indicate that we want to claim the bus */
71 gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
72 udelay(arb->slew_delay_us);
73
74 /* Wait for the other master to release it */
75 stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
76 while (time_before(jiffies, stop_retry)) {
77 int gpio_val = !!gpio_get_value(arb->their_gpio);
78
79 if (gpio_val == arb->their_gpio_release) {
80 /* We got it, so return */
81 return 0;
82 }
83
84 usleep_range(50, 200);
85 }
86
87 /* It didn't release, so give up, wait, and try again */
88 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
89
90 usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
91 } while (time_before(jiffies, stop_time));
92
93 /* Give up, release our claim */
94 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
95 udelay(arb->slew_delay_us);
96 dev_err(&adap->dev, "Could not claim bus, timeout\n");
97 return -EBUSY;
98}
99
100/**
101 * i2c_arbitrator_deselect - release the I2C bus
102 *
103 * Release the I2C bus using the GPIO-based signalling protocol.
104 */
105static int i2c_arbitrator_deselect(struct i2c_adapter *adap, void *data,
106 u32 chan)
107{
108 const struct i2c_arbitrator_data *arb = data;
109
110 /* Release the bus and wait for the other master to notice */
111 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
112 udelay(arb->slew_delay_us);
113
114 return 0;
115}
116
117static int i2c_arbitrator_probe(struct platform_device *pdev)
118{
119 struct device *dev = &pdev->dev;
120 struct device_node *np = dev->of_node;
121 struct device_node *parent_np;
122 struct i2c_arbitrator_data *arb;
123 enum of_gpio_flags gpio_flags;
124 unsigned long out_init;
125 int ret;
126
127 /* We only support probing from device tree; no platform_data */
128 if (!np) {
129 dev_err(dev, "Cannot find device tree node\n");
130 return -ENODEV;
131 }
132 if (dev_get_platdata(dev)) {
133 dev_err(dev, "Platform data is not supported\n");
134 return -EINVAL;
135 }
136
137 arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
138 if (!arb) {
139 dev_err(dev, "Cannot allocate i2c_arbitrator_data\n");
140 return -ENOMEM;
141 }
142 platform_set_drvdata(pdev, arb);
143
144 /* Request GPIOs */
145 ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
146 if (!gpio_is_valid(ret)) {
147 if (ret != -EPROBE_DEFER)
148 dev_err(dev, "Error getting our-claim-gpio\n");
149 return ret;
150 }
151 arb->our_gpio = ret;
152 arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
153 out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
154 GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
155 ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
156 "our-claim-gpio");
157 if (ret) {
158 if (ret != -EPROBE_DEFER)
159 dev_err(dev, "Error requesting our-claim-gpio\n");
160 return ret;
161 }
162
163 ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
164 if (!gpio_is_valid(ret)) {
165 if (ret != -EPROBE_DEFER)
166 dev_err(dev, "Error getting their-claim-gpio\n");
167 return ret;
168 }
169 arb->their_gpio = ret;
170 arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
171 ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
172 "their-claim-gpio");
173 if (ret) {
174 if (ret != -EPROBE_DEFER)
175 dev_err(dev, "Error requesting their-claim-gpio\n");
176 return ret;
177 }
178
179 /* At the moment we only support a single two master (us + 1 other) */
180 if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
181 dev_err(dev, "Only one other master is supported\n");
182 return -EINVAL;
183 }
184
185 /* Arbitration parameters */
186 if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
187 arb->slew_delay_us = 10;
188 if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
189 arb->wait_retry_us = 3000;
190 if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
191 arb->wait_free_us = 50000;
192
193 /* Find our parent */
194 parent_np = of_parse_phandle(np, "i2c-parent", 0);
195 if (!parent_np) {
196 dev_err(dev, "Cannot parse i2c-parent\n");
197 return -EINVAL;
198 }
199 arb->parent = of_get_i2c_adapter_by_node(parent_np);
200 of_node_put(parent_np);
201 if (!arb->parent) {
202 dev_err(dev, "Cannot find parent bus\n");
203 return -EPROBE_DEFER;
204 }
205
206 /* Actually add the mux adapter */
207 arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0,
208 i2c_arbitrator_select,
209 i2c_arbitrator_deselect);
210 if (!arb->child) {
211 dev_err(dev, "Failed to add adapter\n");
212 ret = -ENODEV;
213 i2c_put_adapter(arb->parent);
214 }
215
216 return ret;
217}
218
219static int i2c_arbitrator_remove(struct platform_device *pdev)
220{
221 struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev);
222
223 i2c_del_mux_adapter(arb->child);
224 i2c_put_adapter(arb->parent);
225
226 return 0;
227}
228
229static const struct of_device_id i2c_arbitrator_of_match[] = {
230 { .compatible = "i2c-arb-gpio-challenge", },
231 {},
232};
233MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
234
235static struct platform_driver i2c_arbitrator_driver = {
236 .probe = i2c_arbitrator_probe,
237 .remove = i2c_arbitrator_remove,
238 .driver = {
239 .name = "i2c-arb-gpio-challenge",
240 .of_match_table = i2c_arbitrator_of_match,
241 },
242};
243
244module_platform_driver(i2c_arbitrator_driver);
245
246MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
247MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
248MODULE_LICENSE("GPL v2");
249MODULE_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");