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/init.h>
  23 #include <linux/module.h>
  24 #include <linux/of_i2c.h>
  25 #include <linux/of_gpio.h>
  26 #include <linux/platform_device.h>
  27 #include <linux/slab.h>
  28
  29
  30 /**
  31  * struct i2c_arbitrator_data - Driver data for I2C arbitrator
  32  *
  33  * @parent: Parent adapter
  34  * @child: Child bus
  35  * @our_gpio: GPIO we'll use to claim.
  36  * @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
  37  *   this then consider it released.
  38  * @their_gpio: GPIO that the other side will use to claim.
  39  * @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO ==
  40  *   this then consider it released.
  41  * @slew_delay_us: microseconds to wait for a GPIO to go high.
  42  * @wait_retry_us: we'll attempt another claim after this many microseconds.
  43  * @wait_free_us: we'll give up after this many microseconds.
  44  */
  45
  46 struct i2c_arbitrator_data {
  47         struct i2c_adapter *parent;
  48         struct i2c_adapter *child;
  49         int our_gpio;
  50         int our_gpio_release;
  51         int their_gpio;
  52         int their_gpio_release;
  53         unsigned int slew_delay_us;
  54         unsigned int wait_retry_us;
  55         unsigned int wait_free_us;
  56 };
  57
  58
  59 /**
  60  * i2c_arbitrator_select - claim the I2C bus
  61  *
  62  * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
  63  */
  64 static int i2c_arbitrator_select(struct i2c_adapter *adap, void *data, u32 chan)
  65 {
  66         const struct i2c_arbitrator_data *arb = data;
  67         unsigned long stop_retry, stop_time;
  68
  69         /* Start a round of trying to claim the bus */
  70         stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
  71         do {
  72                 /* Indicate that we want to claim the bus */
  73                 gpio_set_value(arb->our_gpio, !arb->our_gpio_release);
  74                 udelay(arb->slew_delay_us);
  75
  76                 /* Wait for the other master to release it */
  77                 stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
  78                 while (time_before(jiffies, stop_retry)) {
  79                         int gpio_val = !!gpio_get_value(arb->their_gpio);
  80
  81                         if (gpio_val == arb->their_gpio_release) {
  82                                 /* We got it, so return */
  83                                 return 0;
  84                         }
  85
  86                         usleep_range(50, 200);
  87                 }
  88
  89                 /* It didn't release, so give up, wait, and try again */
  90                 gpio_set_value(arb->our_gpio, arb->our_gpio_release);
  91
  92                 usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
  93         } while (time_before(jiffies, stop_time));
  94
  95         /* Give up, release our claim */
  96         gpio_set_value(arb->our_gpio, arb->our_gpio_release);
  97         udelay(arb->slew_delay_us);
  98         dev_err(&adap->dev, "Could not claim bus, timeout\n");
  99         return -EBUSY;
 100 }
 101
 102 /**
 103  * i2c_arbitrator_deselect - release the I2C bus
 104  *
 105  * Release the I2C bus using the GPIO-based signalling protocol.
 106  */
 107 static int i2c_arbitrator_deselect(struct i2c_adapter *adap, void *data,
 108                                    u32 chan)
 109 {
 110         const struct i2c_arbitrator_data *arb = data;
 111
 112         /* Release the bus and wait for the other master to notice */
 113         gpio_set_value(arb->our_gpio, arb->our_gpio_release);
 114         udelay(arb->slew_delay_us);
 115
 116         return 0;
 117 }
 118
 119 static int i2c_arbitrator_probe(struct platform_device *pdev)
 120 {
 121         struct device *dev = &pdev->dev;
 122         struct device_node *np = dev->of_node;
 123         struct device_node *parent_np;
 124         struct i2c_arbitrator_data *arb;
 125         enum of_gpio_flags gpio_flags;
 126         unsigned long out_init;
 127         int ret;
 128
 129         /* We only support probing from device tree; no platform_data */
 130         if (!np) {
 131                 dev_err(dev, "Cannot find device tree node\n");
 132                 return -ENODEV;
 133         }
 134         if (dev->platform_data) {
 135                 dev_err(dev, "Platform data is not supported\n");
 136                 return -EINVAL;
 137         }
 138
 139         arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL);
 140         if (!arb) {
 141                 dev_err(dev, "Cannot allocate i2c_arbitrator_data\n");
 142                 return -ENOMEM;
 143         }
 144         platform_set_drvdata(pdev, arb);
 145
 146         /* Request GPIOs */
 147         ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags);
 148         if (!gpio_is_valid(ret)) {
 149                 if (ret != -EPROBE_DEFER)
 150                         dev_err(dev, "Error getting our-claim-gpio\n");
 151                 return ret;
 152         }
 153         arb->our_gpio = ret;
 154         arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
 155         out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ?
 156                 GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
 157         ret = devm_gpio_request_one(dev, arb->our_gpio, out_init,
 158                                     "our-claim-gpio");
 159         if (ret) {
 160                 if (ret != -EPROBE_DEFER)
 161                         dev_err(dev, "Error requesting our-claim-gpio\n");
 162                 return ret;
 163         }
 164
 165         ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags);
 166         if (!gpio_is_valid(ret)) {
 167                 if (ret != -EPROBE_DEFER)
 168                         dev_err(dev, "Error getting their-claim-gpio\n");
 169                 return ret;
 170         }
 171         arb->their_gpio = ret;
 172         arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW);
 173         ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN,
 174                                     "their-claim-gpio");
 175         if (ret) {
 176                 if (ret != -EPROBE_DEFER)
 177                         dev_err(dev, "Error requesting their-claim-gpio\n");
 178                 return ret;
 179         }
 180
 181         /* At the moment we only support a single two master (us + 1 other) */
 182         if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) {
 183                 dev_err(dev, "Only one other master is supported\n");
 184                 return -EINVAL;
 185         }
 186
 187         /* Arbitration parameters */
 188         if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
 189                 arb->slew_delay_us = 10;
 190         if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
 191                 arb->wait_retry_us = 3000;
 192         if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
 193                 arb->wait_free_us = 50000;
 194
 195         /* Find our parent */
 196         parent_np = of_parse_phandle(np, "i2c-parent", 0);
 197         if (!parent_np) {
 198                 dev_err(dev, "Cannot parse i2c-parent\n");
 199                 return -EINVAL;
 200         }
 201         arb->parent = of_find_i2c_adapter_by_node(parent_np);
 202         if (!arb->parent) {
 203                 dev_err(dev, "Cannot find parent bus\n");
 204                 return -EINVAL;
 205         }
 206
 207         /* Actually add the mux adapter */
 208         arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0,
 209                                          i2c_arbitrator_select,
 210                                          i2c_arbitrator_deselect);
 211         if (!arb->child) {
 212                 dev_err(dev, "Failed to add adapter\n");
 213                 ret = -ENODEV;
 214                 i2c_put_adapter(arb->parent);
 215         }
 216
 217         return ret;
 218 }
 219
 220 static int i2c_arbitrator_remove(struct platform_device *pdev)
 221 {
 222         struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev);
 223
 224         i2c_del_mux_adapter(arb->child);
 225         i2c_put_adapter(arb->parent);
 226
 227         return 0;
 228 }
 229
 230 static const struct of_device_id i2c_arbitrator_of_match[] = {
 231         { .compatible = "i2c-arb-gpio-challenge", },
 232         {},
 233 };
 234 MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
 235
 236 static struct platform_driver i2c_arbitrator_driver = {
 237         .probe  = i2c_arbitrator_probe,
 238         .remove = i2c_arbitrator_remove,
 239         .driver = {
 240                 .owner  = THIS_MODULE,
 241                 .name   = "i2c-arb-gpio-challenge",
 242                 .of_match_table = of_match_ptr(i2c_arbitrator_of_match),
 243         },
 244 };
 245
 246 module_platform_driver(i2c_arbitrator_driver);
 247
 248 MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
 249 MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
 250 MODULE_LICENSE("GPL v2");
 251 MODULE_ALIAS("platform:i2c-arb-gpio-challenge");