LXR linux/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
  28struct 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 */
  42static 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 */
  85static 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
  96static 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
 177static 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
 186static const struct of_device_id i2c_arbitrator_of_match[] = {
 187        { .compatible = "i2c-arb-gpio-challenge", },
 188        {},
 189};
 190MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);
 191
 192static 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
 201module_platform_driver(i2c_arbitrator_driver);
 202
 203MODULE_DESCRIPTION("GPIO-based I2C Arbitration");
 204MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");
 205MODULE_LICENSE("GPL v2");
 206MODULE_ALIAS("platform:i2c-arb-gpio-challenge");
 207