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

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism
   4  *
   5  * Copyright (C) 2012 Google, Inc
   6  */
   7
   8 #include <linux/delay.h>
   9 #include <linux/gpio/consumer.h>
  10 #include <linux/kernel.h>
  11 #include <linux/i2c.h>
  12 #include <linux/i2c-mux.h>
  13 #include <linux/module.h>
  14 #include <linux/platform_device.h>
  15 #include <linux/slab.h>
  16
  17
  18 /**
  19  * struct i2c_arbitrator_data - Driver data for I2C arbitrator
  20  *
  21  * @our_gpio: GPIO descriptor we'll use to claim.
  22  * @their_gpio: GPIO descriptor that the other side will use to claim.
  23  * @slew_delay_us: microseconds to wait for a GPIO to go high.
  24  * @wait_retry_us: we'll attempt another claim after this many microseconds.
  25  * @wait_free_us: we'll give up after this many microseconds.
  26  */
  27
  28 struct i2c_arbitrator_data {
  29         struct gpio_desc *our_gpio;
  30         struct gpio_desc *their_gpio;
  31         unsigned int slew_delay_us;
  32         unsigned int wait_retry_us;
  33         unsigned int wait_free_us;
  34 };
  35
  36
  37 /**
  38  * i2c_arbitrator_select - claim the I2C bus
  39  *
  40  * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
  41  */
  42 static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan)
  43 {
  44         const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
  45         unsigned long stop_retry, stop_time;
  46
  47         /* Start a round of trying to claim the bus */
  48         stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1;
  49         do {
  50                 /* Indicate that we want to claim the bus */
  51                 gpiod_set_value(arb->our_gpio, 1);
  52                 udelay(arb->slew_delay_us);
  53
  54                 /* Wait for the other master to release it */
  55                 stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1;
  56                 while (time_before(jiffies, stop_retry)) {
  57                         int gpio_val = gpiod_get_value(arb->their_gpio);
  58
  59                         if (!gpio_val) {
  60                                 /* We got it, so return */
  61                                 return 0;
  62                         }
  63
  64                         usleep_range(50, 200);
  65                 }
  66
  67                 /* It didn't release, so give up, wait, and try again */
  68                 gpiod_set_value(arb->our_gpio, 0);
  69
  70                 usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2);
  71         } while (time_before(jiffies, stop_time));
  72
  73         /* Give up, release our claim */
  74         gpiod_set_value(arb->our_gpio, 0);
  75         udelay(arb->slew_delay_us);
  76         dev_err(muxc->dev, "Could not claim bus, timeout\n");
  77         return -EBUSY;
  78 }
  79
  80 /**
  81  * i2c_arbitrator_deselect - release the I2C bus
  82  *
  83  * Release the I2C bus using the GPIO-based signalling protocol.
  84  */
  85 static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan)
  86 {
  87         const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc);
  88
  89         /* Release the bus and wait for the other master to notice */
  90         gpiod_set_value(arb->our_gpio, 0);
  91         udelay(arb->slew_delay_us);
  92
  93         return 0;
  94 }
  95
  96 static int i2c_arbitrator_probe(struct platform_device *pdev)
  97 {
  98         struct device *dev = &pdev->dev;
  99         struct device_node *np = dev->of_node;
 100         struct device_node *parent_np;
 101         struct i2c_mux_core *muxc;
 102         struct i2c_arbitrator_data *arb;
 103         struct gpio_desc *dummy;
 104         int ret;
 105
 106         /* We only support probing from device tree; no platform_data */
 107         if (!np) {
 108                 dev_err(dev, "Cannot find device tree node\n");
 109                 return -ENODEV;
 110         }
 111         if (dev_get_platdata(dev)) {
 112                 dev_err(dev, "Platform data is not supported\n");
 113                 return -EINVAL;
 114         }
 115
 116         muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR,
 117                              i2c_arbitrator_select, i2c_arbitrator_deselect);
 118         if (!muxc)
 119                 return -ENOMEM;
 120         arb = i2c_mux_priv(muxc);
 121
 122         platform_set_drvdata(pdev, muxc);
 123
 124         /* Request GPIOs, our GPIO as unclaimed to begin with */
 125         arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW);
 126         if (IS_ERR(arb->our_gpio)) {
 127                 dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n",
 128                         PTR_ERR(arb->our_gpio));
 129                 return PTR_ERR(arb->our_gpio);
 130         }
 131
 132         arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN);
 133         if (IS_ERR(arb->their_gpio)) {
 134                 dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n",
 135                         PTR_ERR(arb->their_gpio));
 136                 return PTR_ERR(arb->their_gpio);
 137         }
 138
 139         /* At the moment we only support a single two master (us + 1 other) */
 140         dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN);
 141         if (!IS_ERR(dummy)) {
 142                 dev_err(dev, "Only one other master is supported\n");
 143                 return -EINVAL;
 144         } else if (PTR_ERR(dummy) == -EPROBE_DEFER) {
 145                 return -EPROBE_DEFER;
 146         }
 147
 148         /* Arbitration parameters */
 149         if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us))
 150                 arb->slew_delay_us = 10;
 151         if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us))
 152                 arb->wait_retry_us = 3000;
 153         if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us))
 154                 arb->wait_free_us = 50000;
 155
 156         /* Find our parent */
 157         parent_np = of_parse_phandle(np, "i2c-parent", 0);
 158         if (!parent_np) {
 159                 dev_err(dev, "Cannot parse i2c-parent\n");
 160                 return -EINVAL;
 161         }
 162         muxc->parent = of_get_i2c_adapter_by_node(parent_np);
 163         of_node_put(parent_np);
 164         if (!muxc->parent) {
 165                 dev_err(dev, "Cannot find parent bus\n");
 166                 return -EPROBE_DEFER;
 167         }
 168
 169         /* Actually add the mux adapter */
 170         ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
 171         if (ret)
 172                 i2c_put_adapter(muxc->parent);
 173
 174         return ret;
 175 }
 176
 177 static int i2c_arbitrator_remove(struct platform_device *pdev)
 178 {
 179         struct i2c_mux_core *muxc = platform_get_drvdata(pdev);
 180
 181         i2c_mux_del_adapters(muxc);
 182         i2c_put_adapter(muxc->parent);
 183         return 0;
 184 }
 185
 186 static const struct of_device_id i2c_arbitrator_of_match[] = {
 187         { .compatible = "i2c-arb-gpio-challenge", },
 188         {},
 189 };
 190 MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
 191
 192 static struct platform_driver i2c_arbitrator_driver = {
 193         .probe  = i2c_arbitrator_probe,
 194         .remove = i2c_arbitrator_remove,
 195         .driver = {
 196                 .name   = "i2c-arb-gpio-challenge",
 197                 .of_match_table = i2c_arbitrator_of_match,
 198         },
 199 };
 200
 201 module_platform_driver(i2c_arbitrator_driver);
 202
 203 MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
 204 MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
 205 MODULE_LICENSE("GPL v2");
 206 MODULE_ALIAS("platform:i2c-arb-gpio-challenge");