Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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> |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 22 | #include <linux/module.h> |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 | * |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 { |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 | */ |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 58 | static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan) |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 59 | { |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 60 | const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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); |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 92 | dev_err(muxc->dev, "Could not claim bus, timeout\n"); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 | */ |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 101 | static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan) |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 102 | { |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 103 | const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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; |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 117 | struct i2c_mux_core *muxc; |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 | } |
Jingoo Han | 6d4028c | 2013-07-30 16:59:33 +0900 | [diff] [blame] | 128 | if (dev_get_platdata(dev)) { |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 129 | dev_err(dev, "Platform data is not supported\n"); |
| 130 | return -EINVAL; |
| 131 | } |
| 132 | |
Peter Rosin | 4083959 | 2016-08-11 16:49:54 +0200 | [diff] [blame] | 133 | muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR, |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 134 | i2c_arbitrator_select, i2c_arbitrator_deselect); |
| 135 | if (!muxc) |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 136 | return -ENOMEM; |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 137 | arb = i2c_mux_priv(muxc); |
| 138 | |
| 139 | platform_set_drvdata(pdev, muxc); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 | } |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 196 | muxc->parent = of_get_i2c_adapter_by_node(parent_np); |
Vladimir Zapolskiy | bdbf4a2 | 2015-08-26 23:59:33 +0300 | [diff] [blame] | 197 | of_node_put(parent_np); |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 198 | if (!muxc->parent) { |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 199 | dev_err(dev, "Cannot find parent bus\n"); |
Wolfram Sang | 0cd9806 | 2013-10-10 10:19:13 +0200 | [diff] [blame] | 200 | return -EPROBE_DEFER; |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 201 | } |
| 202 | |
| 203 | /* Actually add the mux adapter */ |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 204 | ret = i2c_mux_add_adapter(muxc, 0, 0, 0); |
| 205 | if (ret) { |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 206 | dev_err(dev, "Failed to add adapter\n"); |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 207 | i2c_put_adapter(muxc->parent); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 208 | } |
| 209 | |
| 210 | return ret; |
| 211 | } |
| 212 | |
| 213 | static int i2c_arbitrator_remove(struct platform_device *pdev) |
| 214 | { |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 215 | struct i2c_mux_core *muxc = platform_get_drvdata(pdev); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 216 | |
Peter Rosin | 8aacd90 | 2016-04-20 08:39:46 +0200 | [diff] [blame] | 217 | i2c_mux_del_adapters(muxc); |
| 218 | i2c_put_adapter(muxc->parent); |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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 = { |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 232 | .name = "i2c-arb-gpio-challenge", |
Sachin Kamat | 4e90532 | 2013-09-30 09:04:25 +0530 | [diff] [blame] | 233 | .of_match_table = i2c_arbitrator_of_match, |
Doug Anderson | b81dfaa | 2013-04-16 06:29:00 +0000 | [diff] [blame] | 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"); |