drivers/i2c/muxes/i2c-arb-gpio-challenge.c

   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
  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         }
 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_find_i2c_adapter_by_node(parent_np);
 200         if (!arb->parent) {
 201                 dev_err(dev, "Cannot find parent bus\n");
 202                 return -EPROBE_DEFER;
 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 = {
 238                 .name   = "i2c-arb-gpio-challenge",
 239                 .of_match_table = i2c_arbitrator_of_match,
 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");