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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism4 *5 * Copyright (C) 2012 Google, Inc6 */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 arbitrator20 *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 bus39 *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 bus82 *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);171 if (ret)172 i2c_put_adapter(muxc->parent);173 174 return ret;175}176 177static void 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}184 185static const struct of_device_id i2c_arbitrator_of_match[] = {186 { .compatible = "i2c-arb-gpio-challenge", },187 {},188};189MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match);190 191static struct platform_driver i2c_arbitrator_driver = {192 .probe = i2c_arbitrator_probe,193 .remove_new = i2c_arbitrator_remove,194 .driver = {195 .name = "i2c-arb-gpio-challenge",196 .of_match_table = i2c_arbitrator_of_match,197 },198};199 200module_platform_driver(i2c_arbitrator_driver);201 202MODULE_DESCRIPTION("GPIO-based I2C Arbitration");203MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>");204MODULE_LICENSE("GPL v2");205MODULE_ALIAS("platform:i2c-arb-gpio-challenge");206