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