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b81dfaa0 DA |
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 | * | |
b81dfaa0 DA |
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 | ||
42 | struct i2c_arbitrator_data { | |
b81dfaa0 DA |
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 | */ | |
8aacd901 | 58 | static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan) |
b81dfaa0 | 59 | { |
8aacd901 | 60 | const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc); |
b81dfaa0 DA |
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); | |
8aacd901 | 92 | dev_err(muxc->dev, "Could not claim bus, timeout\n"); |
b81dfaa0 DA |
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 | */ | |
8aacd901 | 101 | static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan) |
b81dfaa0 | 102 | { |
8aacd901 | 103 | const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc); |
b81dfaa0 DA |
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 | ||
112 | static 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; | |
8aacd901 | 117 | struct i2c_mux_core *muxc; |
b81dfaa0 DA |
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 | } | |
6d4028c6 | 128 | if (dev_get_platdata(dev)) { |
b81dfaa0 DA |
129 | dev_err(dev, "Platform data is not supported\n"); |
130 | return -EINVAL; | |
131 | } | |
132 | ||
8aacd901 PR |
133 | muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), 0, |
134 | i2c_arbitrator_select, i2c_arbitrator_deselect); | |
135 | if (!muxc) | |
b81dfaa0 | 136 | return -ENOMEM; |
8aacd901 PR |
137 | arb = i2c_mux_priv(muxc); |
138 | ||
139 | platform_set_drvdata(pdev, muxc); | |
b81dfaa0 DA |
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 | } | |
8aacd901 | 196 | muxc->parent = of_get_i2c_adapter_by_node(parent_np); |
bdbf4a29 | 197 | of_node_put(parent_np); |
8aacd901 | 198 | if (!muxc->parent) { |
b81dfaa0 | 199 | dev_err(dev, "Cannot find parent bus\n"); |
0cd98069 | 200 | return -EPROBE_DEFER; |
b81dfaa0 DA |
201 | } |
202 | ||
203 | /* Actually add the mux adapter */ | |
8aacd901 PR |
204 | ret = i2c_mux_add_adapter(muxc, 0, 0, 0); |
205 | if (ret) { | |
b81dfaa0 | 206 | dev_err(dev, "Failed to add adapter\n"); |
8aacd901 | 207 | i2c_put_adapter(muxc->parent); |
b81dfaa0 DA |
208 | } |
209 | ||
210 | return ret; | |
211 | } | |
212 | ||
213 | static int i2c_arbitrator_remove(struct platform_device *pdev) | |
214 | { | |
8aacd901 | 215 | struct i2c_mux_core *muxc = platform_get_drvdata(pdev); |
b81dfaa0 | 216 | |
8aacd901 PR |
217 | i2c_mux_del_adapters(muxc); |
218 | i2c_put_adapter(muxc->parent); | |
b81dfaa0 DA |
219 | return 0; |
220 | } | |
221 | ||
222 | static const struct of_device_id i2c_arbitrator_of_match[] = { | |
223 | { .compatible = "i2c-arb-gpio-challenge", }, | |
224 | {}, | |
225 | }; | |
226 | MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match); | |
227 | ||
228 | static struct platform_driver i2c_arbitrator_driver = { | |
229 | .probe = i2c_arbitrator_probe, | |
230 | .remove = i2c_arbitrator_remove, | |
231 | .driver = { | |
b81dfaa0 | 232 | .name = "i2c-arb-gpio-challenge", |
4e905323 | 233 | .of_match_table = i2c_arbitrator_of_match, |
b81dfaa0 DA |
234 | }, |
235 | }; | |
236 | ||
237 | module_platform_driver(i2c_arbitrator_driver); | |
238 | ||
239 | MODULE_DESCRIPTION("GPIO-based I2C Arbitration"); | |
240 | MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>"); | |
241 | MODULE_LICENSE("GPL v2"); | |
242 | MODULE_ALIAS("platform:i2c-arb-gpio-challenge"); |