diff options
| -rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt | 80 | ||||
| -rw-r--r-- | drivers/i2c/muxes/Kconfig | 12 | ||||
| -rw-r--r-- | drivers/i2c/muxes/Makefile | 2 | ||||
| -rw-r--r-- | drivers/i2c/muxes/i2c-arb-gpio-challenge.c | 251 |
4 files changed, 345 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt new file mode 100644 index 000000000000..1ac8ea8ade1d --- /dev/null +++ b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt @@ -0,0 +1,80 @@ +GPIO-based I2C Arbitration Using a Challenge & Response Mechanism +================================================================= +This uses GPIO lines and a challenge & response mechanism to arbitrate who is +the master of an I2C bus in a multimaster situation. + +In many cases using GPIOs to arbitrate is not needed and a design can use +the standard I2C multi-master rules. Using GPIOs is generally useful in +the case where there is a device on the bus that has errata and/or bugs +that makes standard multimaster mode not feasible. + + +Algorithm: + +All masters on the bus have a 'bus claim' line which is an output that the +others can see. These are all active low with pull-ups enabled. We'll +describe these lines as: + +- OUR_CLAIM: output from us signaling to other hosts that we want the bus +- THEIR_CLAIMS: output from others signaling that they want the bus + +The basic algorithm is to assert your line when you want the bus, then make +sure that the other side doesn't want it also. A detailed explanation is best +done with an example. + +Let's say we want to claim the bus. We: +1. Assert OUR_CLAIM. +2. Waits a little bit for the other sides to notice (slew time, say 10 + microseconds). +3. Check THEIR_CLAIMS. If none are asserted then the we have the bus and we are + done. +4. Otherwise, wait for a few milliseconds and see if THEIR_CLAIMS are released. +5. If not, back off, release the claim and wait for a few more milliseconds. +6. Go back to 1 (until retry time has expired). + + +Required properties: +- compatible: i2c-arb-gpio-challenge +- our-claim-gpio: The GPIO that we use to claim the bus. +- their-claim-gpios: The GPIOs that the other sides use to claim the bus. + Note that some implementations may only support a single other master. +- Standard I2C mux properties. See mux.txt in this directory. +- Single I2C child bus node at reg 0. See mux.txt in this directory. + +Optional properties: +- slew-delay-us: microseconds to wait for a GPIO to go high. Default is 10 us. +- wait-retry-us: we'll attempt another claim after this many microseconds. + Default is 3000 us. +- wait-free-us: we'll give up after this many microseconds. Default is 50000 us. + + +Example: + i2c@12CA0000 { + compatible = "acme,some-i2c-device"; + #address-cells = <1>; + #size-cells = <0>; + }; + + i2c-arbitrator { + compatible = "i2c-arb-gpio-challenge"; + #address-cells = <1>; + #size-cells = <0>; + + i2c-parent = <&{/i2c@12CA0000}>; + + our-claim-gpio = <&gpf0 3 1>; + their-claim-gpios = <&gpe0 4 1>; + slew-delay-us = <10>; + wait-retry-us = <3000>; + wait-free-us = <50000>; + + i2c@0 { + reg = <0>; + #address-cells = <1>; + #size-cells = <0>; + + i2c@52 { + // Normal I2C device + }; + }; + }; diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig index 0be5b83c08fa..5faf244d2476 100644 --- a/drivers/i2c/muxes/Kconfig +++ b/drivers/i2c/muxes/Kconfig @@ -5,6 +5,18 @@ menu "Multiplexer I2C Chip support" depends on I2C_MUX +config I2C_ARB_GPIO_CHALLENGE + tristate "GPIO-based I2C arbitration" + depends on GENERIC_GPIO && OF + help + If you say yes to this option, support will be included for an + I2C multimaster arbitration scheme using GPIOs and a challenge & + response mechanism where masters have to claim the bus by asserting + a GPIO. + + This driver can also be built as a module. If so, the module + will be called i2c-arb-gpio-challenge. + config I2C_MUX_GPIO tristate "GPIO-based I2C multiplexer" depends on GENERIC_GPIO diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile index 76da8692afff..465778b5d5dc 100644 --- a/drivers/i2c/muxes/Makefile +++ b/drivers/i2c/muxes/Makefile @@ -1,6 +1,8 @@ # # Makefile for multiplexer I2C chip drivers. +obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE) += i2c-arb-gpio-challenge.o + obj-$(CONFIG_I2C_MUX_GPIO) += i2c-mux-gpio.o obj-$(CONFIG_I2C_MUX_PCA9541) += i2c-mux-pca9541.o obj-$(CONFIG_I2C_MUX_PCA954x) += i2c-mux-pca954x.o 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 000000000000..210b6f7b9028 --- /dev/null +++ b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c @@ -0,0 +1,251 @@ +/* + * GPIO-based I2C Arbitration Using a Challenge & Response Mechanism + * + * Copyright (C) 2012 Google, Inc + * + * This software is licensed under the terms of the GNU General Public + * License version 2, as published by the Free Software Foundation, and + * may be copied, distributed, and modified under those terms. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + */ + +#include <linux/delay.h> +#include <linux/gpio.h> +#include <linux/kernel.h> +#include <linux/i2c.h> +#include <linux/i2c-mux.h> +#include <linux/init.h> +#include <linux/module.h> +#include <linux/of_i2c.h> +#include <linux/of_gpio.h> +#include <linux/platform_device.h> +#include <linux/slab.h> + + +/** + * struct i2c_arbitrator_data - Driver data for I2C arbitrator + * + * @parent: Parent adapter + * @child: Child bus + * @our_gpio: GPIO we'll use to claim. + * @our_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO == + * this then consider it released. + * @their_gpio: GPIO that the other side will use to claim. + * @their_gpio_release: 0 if active high; 1 if active low; AKA if the GPIO == + * this then consider it released. + * @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 i2c_adapter *parent; + struct i2c_adapter *child; + int our_gpio; + int our_gpio_release; + int their_gpio; + int their_gpio_release; + 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_adapter *adap, void *data, u32 chan) +{ + const struct i2c_arbitrator_data *arb = data; + 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 */ + gpio_set_value(arb->our_gpio, !arb->our_gpio_release); + 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 = !!gpio_get_value(arb->their_gpio); + + if (gpio_val == arb->their_gpio_release) { + /* We got it, so return */ + return 0; + } + + usleep_range(50, 200); + } + + /* It didn't release, so give up, wait, and try again */ + gpio_set_value(arb->our_gpio, arb->our_gpio_release); + + usleep_range(arb->wait_retry_us, arb->wait_retry_us * 2); + } while (time_before(jiffies, stop_time)); + + /* Give up, release our claim */ + gpio_set_value(arb->our_gpio, arb->our_gpio_release); + udelay(arb->slew_delay_us); + dev_err(&adap->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_adapter *adap, void *data, + u32 chan) +{ + const struct i2c_arbitrator_data *arb = data; + + /* Release the bus and wait for the other master to notice */ + gpio_set_value(arb->our_gpio, arb->our_gpio_release); + 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_arbitrator_data *arb; + enum of_gpio_flags gpio_flags; + unsigned long out_init; + 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->platform_data) { + dev_err(dev, "Platform data is not supported\n"); + return -EINVAL; + } + + arb = devm_kzalloc(dev, sizeof(*arb), GFP_KERNEL); + if (!arb) { + dev_err(dev, "Cannot allocate i2c_arbitrator_data\n"); + return -ENOMEM; + } + platform_set_drvdata(pdev, arb); + + /* Request GPIOs */ + ret = of_get_named_gpio_flags(np, "our-claim-gpio", 0, &gpio_flags); + if (!gpio_is_valid(ret)) { + if (ret != -EPROBE_DEFER) + dev_err(dev, "Error getting our-claim-gpio\n"); + return ret; + } + arb->our_gpio = ret; + arb->our_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW); + out_init = (gpio_flags & OF_GPIO_ACTIVE_LOW) ? + GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW; + ret = devm_gpio_request_one(dev, arb->our_gpio, out_init, + "our-claim-gpio"); + if (ret) { + if (ret != -EPROBE_DEFER) + dev_err(dev, "Error requesting our-claim-gpio\n"); + return ret; + } + + ret = of_get_named_gpio_flags(np, "their-claim-gpios", 0, &gpio_flags); + if (!gpio_is_valid(ret)) { + if (ret != -EPROBE_DEFER) + dev_err(dev, "Error getting their-claim-gpio\n"); + return ret; + } + arb->their_gpio = ret; + arb->their_gpio_release = !!(gpio_flags & OF_GPIO_ACTIVE_LOW); + ret = devm_gpio_request_one(dev, arb->their_gpio, GPIOF_IN, + "their-claim-gpio"); + if (ret) { + if (ret != -EPROBE_DEFER) + dev_err(dev, "Error requesting their-claim-gpio\n"); + return ret; + } + + /* At the moment we only support a single two master (us + 1 other) */ + if (gpio_is_valid(of_get_named_gpio(np, "their-claim-gpios", 1))) { + dev_err(dev, "Only one other master is supported\n"); + return -EINVAL; + } + + /* 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; + } + arb->parent = of_find_i2c_adapter_by_node(parent_np); + if (!arb->parent) { + dev_err(dev, "Cannot find parent bus\n"); + return -EINVAL; + } + + /* Actually add the mux adapter */ + arb->child = i2c_add_mux_adapter(arb->parent, dev, arb, 0, 0, 0, + i2c_arbitrator_select, + i2c_arbitrator_deselect); + if (!arb->child) { + dev_err(dev, "Failed to add adapter\n"); + ret = -ENODEV; + i2c_put_adapter(arb->parent); + } + + return ret; +} + +static int i2c_arbitrator_remove(struct platform_device *pdev) +{ + struct i2c_arbitrator_data *arb = platform_get_drvdata(pdev); + + i2c_del_mux_adapter(arb->child); + i2c_put_adapter(arb->parent); + + return 0; +} + +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 = i2c_arbitrator_remove, + .driver = { + .owner = THIS_MODULE, + .name = "i2c-arb-gpio-challenge", + .of_match_table = of_match_ptr(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"); |