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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> | |
b81dfaa0 | 22 | #include <linux/module.h> |
b81dfaa0 DA |
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 | ||
44 | struct 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 | */ | |
62 | static 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 | */ | |
105 | static 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 | ||
117 | static 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 | } | |
6d4028c6 | 132 | if (dev_get_platdata(dev)) { |
b81dfaa0 DA |
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_find_i2c_adapter_by_node(parent_np); | |
200 | if (!arb->parent) { | |
201 | dev_err(dev, "Cannot find parent bus\n"); | |
0cd98069 | 202 | return -EPROBE_DEFER; |
b81dfaa0 DA |
203 | } |
204 | ||
205 | /* Actually add the mux adapter */ | |
206 | arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0, | |
207 | i2c_arbitrator_select, | |
208 | i2c_arbitrator_deselect); | |
209 | if (!arb->child) { | |
210 | dev_err(dev, "Failed to add adapter\n"); | |
211 | ret = -ENODEV; | |
212 | i2c_put_adapter(arb->parent); | |
213 | } | |
214 | ||
215 | return ret; | |
216 | } | |
217 | ||
218 | static int i2c_arbitrator_remove(struct platform_device *pdev) | |
219 | { | |
220 | struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev); | |
221 | ||
222 | i2c_del_mux_adapter(arb->child); | |
223 | i2c_put_adapter(arb->parent); | |
224 | ||
225 | return 0; | |
226 | } | |
227 | ||
228 | static const struct of_device_id i2c_arbitrator_of_match[] = { | |
229 | { .compatible = "i2c-arb-gpio-challenge", }, | |
230 | {}, | |
231 | }; | |
232 | MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match); | |
233 | ||
234 | static struct platform_driver i2c_arbitrator_driver = { | |
235 | .probe = i2c_arbitrator_probe, | |
236 | .remove = i2c_arbitrator_remove, | |
237 | .driver = { | |
b81dfaa0 | 238 | .name = "i2c-arb-gpio-challenge", |
4e905323 | 239 | .of_match_table = i2c_arbitrator_of_match, |
b81dfaa0 DA |
240 | }, |
241 | }; | |
242 | ||
243 | module_platform_driver(i2c_arbitrator_driver); | |
244 | ||
245 | MODULE_DESCRIPTION("GPIO-based I2C Arbitration"); | |
246 | MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>"); | |
247 | MODULE_LICENSE("GPL v2"); | |
248 | MODULE_ALIAS("platform:i2c-arb-gpio-challenge"); |