diff options
Diffstat (limited to 'drivers/i2c/muxes/i2c-arb-gpio-challenge.c')
| -rw-r--r-- | drivers/i2c/muxes/i2c-arb-gpio-challenge.c | 205 |
1 files changed, 205 insertions, 0 deletions
diff --git a/drivers/i2c/muxes/i2c-arb-gpio-challenge.c b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c new file mode 100644 index 0000000000..24168e9f7d --- /dev/null +++ b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c @@ -0,0 +1,205 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism + * + * Copyright (C) 2012 Google, Inc + */ + +#include <linux/delay.h> +#include <linux/gpio/consumer.h> +#include <linux/kernel.h> +#include <linux/i2c.h> +#include <linux/i2c-mux.h> +#include <linux/module.h> +#include <linux/platform_device.h> +#include <linux/slab.h> + + +/** + * struct i2c_arbitrator_data - Driver data for I2C arbitrator + * + * @our_gpio: GPIO descriptor we'll use to claim. + * @their_gpio: GPIO descriptor that the other side will use to claim. + * @slew_delay_us: microseconds to wait for a GPIO to go high. + * @wait_retry_us: we'll attempt another claim after this many microseconds. + * @wait_free_us: we'll give up after this many microseconds. + */ + +struct i2c_arbitrator_data { + struct gpio_desc *our_gpio; + struct gpio_desc *their_gpio; + unsigned int slew_delay_us; + unsigned int wait_retry_us; + unsigned int wait_free_us; +}; + + +/* + * i2c_arbitrator_select - claim the I2C bus + * + * Use the GPIO-based signalling protocol; return -EBUSY if we fail. + */ +static int i2c_arbitrator_select(struct i2c_mux_core *muxc, u32 chan) +{ + const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc); + unsigned long stop_retry, stop_time; + + /* Start a round of trying to claim the bus */ + stop_time = jiffies + usecs_to_jiffies(arb->wait_free_us) + 1; + do { + /* Indicate that we want to claim the bus */ + gpiod_set_value(arb->our_gpio, 1); + udelay(arb->slew_delay_us); + + /* Wait for the other master to release it */ + stop_retry = jiffies + usecs_to_jiffies(arb->wait_retry_us) + 1; + while (time_before(jiffies, stop_retry)) { + int gpio_val = gpiod_get_value(arb->their_gpio); + + if (!gpio_val) { + /* We got it, so return */ + return 0; + } + + usleep_range(50, 200); + } + + /* It didn't release, so give up, wait, and try again */ + gpiod_set_value(arb->our_gpio, 0); + + usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2); + } while (time_before(jiffies, stop_time)); + + /* Give up, release our claim */ + gpiod_set_value(arb->our_gpio, 0); + udelay(arb->slew_delay_us); + dev_err(muxc->dev, "Could not claim bus, timeout\n"); + return -EBUSY; +} + +/* + * i2c_arbitrator_deselect - release the I2C bus + * + * Release the I2C bus using the GPIO-based signalling protocol. + */ +static int i2c_arbitrator_deselect(struct i2c_mux_core *muxc, u32 chan) +{ + const struct i2c_arbitrator_data *arb = i2c_mux_priv(muxc); + + /* Release the bus and wait for the other master to notice */ + gpiod_set_value(arb->our_gpio, 0); + udelay(arb->slew_delay_us); + + return 0; +} + +static int i2c_arbitrator_probe(struct platform_device *pdev) +{ + struct device *dev = &pdev->dev; + struct device_node *np = dev->of_node; + struct device_node *parent_np; + struct i2c_mux_core *muxc; + struct i2c_arbitrator_data *arb; + struct gpio_desc *dummy; + int ret; + + /* We only support probing from device tree; no platform_data */ + if (!np) { + dev_err(dev, "Cannot find device tree node\n"); + return -ENODEV; + } + if (dev_get_platdata(dev)) { + dev_err(dev, "Platform data is not supported\n"); + return -EINVAL; + } + + muxc = i2c_mux_alloc(NULL, dev, 1, sizeof(*arb), I2C_MUX_ARBITRATOR, + i2c_arbitrator_select, i2c_arbitrator_deselect); + if (!muxc) + return -ENOMEM; + arb = i2c_mux_priv(muxc); + + platform_set_drvdata(pdev, muxc); + + /* Request GPIOs, our GPIO as unclaimed to begin with */ + arb->our_gpio = devm_gpiod_get(dev, "our-claim", GPIOD_OUT_LOW); + if (IS_ERR(arb->our_gpio)) { + dev_err(dev, "could not get \"our-claim\" GPIO (%ld)\n", + PTR_ERR(arb->our_gpio)); + return PTR_ERR(arb->our_gpio); + } + + arb->their_gpio = devm_gpiod_get(dev, "their-claim", GPIOD_IN); + if (IS_ERR(arb->their_gpio)) { + dev_err(dev, "could not get \"their-claim\" GPIO (%ld)\n", + PTR_ERR(arb->their_gpio)); + return PTR_ERR(arb->their_gpio); + } + + /* At the moment we only support a single two master (us + 1 other) */ + dummy = devm_gpiod_get_index(dev, "their-claim", 1, GPIOD_IN); + if (!IS_ERR(dummy)) { + dev_err(dev, "Only one other master is supported\n"); + return -EINVAL; + } else if (PTR_ERR(dummy) == -EPROBE_DEFER) { + return -EPROBE_DEFER; + } + + /* Arbitration parameters */ + if (of_property_read_u32(np, "slew-delay-us", &arb->slew_delay_us)) + arb->slew_delay_us = 10; + if (of_property_read_u32(np, "wait-retry-us", &arb->wait_retry_us)) + arb->wait_retry_us = 3000; + if (of_property_read_u32(np, "wait-free-us", &arb->wait_free_us)) + arb->wait_free_us = 50000; + + /* Find our parent */ + parent_np = of_parse_phandle(np, "i2c-parent", 0); + if (!parent_np) { + dev_err(dev, "Cannot parse i2c-parent\n"); + return -EINVAL; + } + muxc->parent = of_get_i2c_adapter_by_node(parent_np); + of_node_put(parent_np); + if (!muxc->parent) { + dev_err(dev, "Cannot find parent bus\n"); + return -EPROBE_DEFER; + } + + /* Actually add the mux adapter */ + ret = i2c_mux_add_adapter(muxc, 0, 0, 0); + if (ret) + i2c_put_adapter(muxc->parent); + + return ret; +} + +static void i2c_arbitrator_remove(struct platform_device *pdev) +{ + struct i2c_mux_core *muxc = platform_get_drvdata(pdev); + + i2c_mux_del_adapters(muxc); + i2c_put_adapter(muxc->parent); +} + +static const struct of_device_id i2c_arbitrator_of_match[] = { + { .compatible = "i2c-arb-gpio-challenge", }, + {}, +}; +MODULE_DEVICE_TABLE(of, i2c_arbitrator_of_match); + +static struct platform_driver i2c_arbitrator_driver = { + .probe = i2c_arbitrator_probe, + .remove_new = i2c_arbitrator_remove, + .driver = { + .name = "i2c-arb-gpio-challenge", + .of_match_table = i2c_arbitrator_of_match, + }, +}; + +module_platform_driver(i2c_arbitrator_driver); + +MODULE_DESCRIPTION("GPIO-based I2C Arbitration"); +MODULE_AUTHOR("Doug Anderson <dianders@chromium.org>"); +MODULE_LICENSE("GPL v2"); +MODULE_ALIAS("platform:i2c-arb-gpio-challenge"); |