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  * @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 {
  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  */
  58 static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
  59 {
  60         const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
  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);
  92         dev_err(muxc->dev, "Could not claim bus, timeout\n");
  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  */
 101 static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
 102 {
 103         const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
 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;
 117         struct i2c_mux_core *muxc;
 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         }
 128         if (dev_get_platdata(dev)) {
 129                 dev_err(dev, "Platform data is not supported\n");
 130                 return -EINVAL;
 131         }
 132
 133         muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), 0,
 134                              i2c_arbitrator_select, i2c_arbitrator_deselect);
 135         if (!muxc)
 136                 return -ENOMEM;
 137         arb = i2c_mux_priv(muxc);
 138
 139         platform_set_drvdata(pdev, muxc);
 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         }
 196         muxc->parent = of_get_i2c_adapter_by_node(parent_np);
 197         of_node_put(parent_np);
 198         if (!muxc->parent) {
 199                 dev_err(dev, "Cannot find parent bus\n");
 200                 return -EPROBE_DEFER;
 201         }
 202
 203         /* Actually add the mux adapter */
 204         ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
 205         if (ret) {
 206                 dev_err(dev, "Failed to add adapter\n");
 207                 i2c_put_adapter(muxc->parent);
 208         }
 209
 210         return ret;
 211 }
 212
 213 static int i2c_arbitrator_remove(struct platform_device *pdev)
 214 {
 215         struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
 216
 217         i2c_mux_del_adapters(muxc);
 218         i2c_put_adapter(muxc->parent);
 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 = {
 232                 .name   = "i2c-arb-gpio-challenge",
 233                 .of_match_table = i2c_arbitrator_of_match,
 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");