realtek: add new i2c-gpio-shared driver for shared SCL lines
Some Realtek switches have been designed with I2C busses that share a single SCL line. The clock line is used for 2 or more busses. This cannot be used with the standard i2c-gpio driver that relies on distinct SDA and SCL pairs. Provide a derived i2c-gpio-shared driver that can be used instead. This driver can handle up to 4 busses with only a single clock line. Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de> Link: https://github.com/openwrt/openwrt/pull/18737 Signed-off-by: Robert Marko <robimarko@gmail.com>
This commit is contained in:
Markus Stockhausen
Robert Marko
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commit
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3 changed files with 271 additions and 0 deletions
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# SPDX-License-Identifier: GPL-2.0
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%YAML 1.2
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---
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$id: http://devicetree.org/schemas/i2c/i2c-gpio-shared.yaml#
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$schema: http://devicetree.org/meta-schemas/core.yaml#
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title: mulitple GPIO bitbanged I2C busses with shared SCL
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maintainers:
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- Markus Stockhausen <markus.stockhausen@gmx.de>
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allOf:
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- $ref: /schemas/i2c/i2c-controller.yaml#
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properties:
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compatible:
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items:
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- const: i2c-gpio-shared
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scl-gpios:
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description:
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gpio used for the shared scl signal, this should be flagged as
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active high using open drain with (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)
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from <dt-bindings/gpio/gpio.h> since the signal is by definition
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open drain.
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maxItems: 1
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examples:
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- |
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#include <dt-bindings/gpio/gpio.h>
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i2c-gpio-shared {
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compatible = "i2c-gpio-shared";
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scl-gpios = <&gpio1 31 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
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#address-cells = <1>;
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#size-cells = <0>;
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i2c0: i2c@0 {
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sda-gpios = <&gpio1 6 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
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i2c-gpio,delay-us = <2>;
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};
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i2c1: i2c@1 {
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sda-gpios = <&gpio1 7 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
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i2c-gpio,delay-us = <2>;
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};
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};
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required:
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- compatible
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- scl-gpios
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@ -0,0 +1,179 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Bitbanging driver for multiple I2C busses with shared SCL pin using the GPIO API
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* Copyright (c) 2025 Markus Stockhausen <markus.stockhausen at gmx.de>
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*/
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#include <linux/i2c-algo-bit.h>
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#include <linux/gpio/consumer.h>
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#include <linux/mod_devicetable.h>
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#include <linux/mutex.h>
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#include <linux/platform_device.h>
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struct gpio_shared_ctx;
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struct gpio_shared_bus {
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int num;
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struct gpio_desc *sda;
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struct i2c_adapter adap;
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struct i2c_algo_bit_data bit_data;
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struct gpio_shared_ctx *ctx;
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};
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#define GPIO_SHARED_MAX_BUS 4
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struct gpio_shared_ctx {
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struct device *dev;
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struct gpio_desc *scl;
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struct mutex lock;
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struct gpio_shared_bus bus[GPIO_SHARED_MAX_BUS];
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};
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static void gpio_shared_setsda(void *data, int state)
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{
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struct gpio_shared_bus *bus = data;
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gpiod_set_value_cansleep(bus->sda, state);
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}
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static void gpio_shared_setscl(void *data, int state)
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{
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struct gpio_shared_bus *bus = data;
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struct gpio_shared_ctx *ctx = bus->ctx;
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gpiod_set_value_cansleep(ctx->scl, state);
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}
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static int gpio_shared_getsda(void *data)
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{
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struct gpio_shared_bus *bus = data;
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return gpiod_get_value_cansleep(bus->sda);
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}
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static int gpio_shared_getscl(void *data)
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{
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struct gpio_shared_bus *bus = data;
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struct gpio_shared_ctx *ctx = bus->ctx;
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return gpiod_get_value_cansleep(ctx->scl);
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}
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static int gpio_shared_pre_xfer(struct i2c_adapter *adap)
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{
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struct gpio_shared_bus *bus = container_of(adap, typeof(*bus), adap);
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struct gpio_shared_ctx *ctx = bus->ctx;
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mutex_lock(&ctx->lock);
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dev_dbg(ctx->dev, "lock before transfer to bus %d\n", bus->num);
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return 0;
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}
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static void gpio_shared_post_xfer(struct i2c_adapter *adap)
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{
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struct gpio_shared_bus *bus = container_of(adap, typeof(*bus), adap);
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struct gpio_shared_ctx *ctx = bus->ctx;
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dev_dbg(ctx->dev, "unlock after transfer to bus %d\n", bus->num);
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mutex_unlock(&ctx->lock);
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}
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static int gpio_shared_probe(struct platform_device *pdev)
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{
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struct device *dev = &pdev->dev;
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struct fwnode_handle *child;
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struct gpio_shared_ctx *ctx;
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int msecs, ret, bus_num = -1;
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ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return -ENOMEM;
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ctx->dev = dev;
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mutex_init(&ctx->lock);
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ctx->scl = devm_gpiod_get(dev, "scl", GPIOD_OUT_HIGH_OPEN_DRAIN);
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if (IS_ERR(ctx->scl))
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return dev_err_probe(dev, PTR_ERR(ctx->scl), "shared SCL node not found\n");
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if (device_get_child_node_count(dev) >= GPIO_SHARED_MAX_BUS)
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return dev_err_probe(dev, -EINVAL, "Too many channels\n");
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device_for_each_child_node(dev, child) {
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struct gpio_shared_bus *bus = &ctx->bus[++bus_num];
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struct i2c_adapter *adap = &bus->adap;
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struct i2c_algo_bit_data *bit_data = &bus->bit_data;
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bus->sda = devm_fwnode_gpiod_get(dev, child, "sda", GPIOD_OUT_HIGH_OPEN_DRAIN,
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fwnode_get_name(child));
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if (IS_ERR(bus->sda)) {
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fwnode_handle_put(child);
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dev_err(dev, "SDA node for bus %d not found\n", bus_num);
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continue;
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}
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bus->num = bus_num;
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bus->ctx = ctx;
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bit_data->data = bus;
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bit_data->setsda = gpio_shared_setsda;
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bit_data->setscl = gpio_shared_setscl;
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bit_data->pre_xfer = gpio_shared_pre_xfer;
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bit_data->post_xfer = gpio_shared_post_xfer;
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if (fwnode_property_read_u32(child, "i2c-gpio,delay-us", &bit_data->udelay))
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bit_data->udelay = 5;
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if (!fwnode_property_read_bool(child, "i2c-gpio,sda-output-only"))
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bit_data->getsda = gpio_shared_getsda;
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if (!device_property_read_bool(dev, "i2c-gpio,scl-output-only"))
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bit_data->getscl = gpio_shared_getscl;
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if (!device_property_read_u32(dev, "i2c-gpio,timeout-ms", &msecs))
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bit_data->timeout = msecs_to_jiffies(msecs);
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else
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bit_data->timeout = HZ / 10; /* 100ms */
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if (gpiod_cansleep(bus->sda) || gpiod_cansleep(ctx->scl))
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dev_warn(dev, "Slow GPIO pins might wreak havoc into I2C/SMBus bus timing");
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else
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bit_data->can_do_atomic = true;
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adap->owner = THIS_MODULE;
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strscpy(adap->name, KBUILD_MODNAME, sizeof(adap->name));
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adap->dev.parent = dev;
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device_set_node(&adap->dev, child);
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adap->algo_data = &bus->bit_data;
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adap->class = I2C_CLASS_HWMON;
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ret = i2c_bit_add_bus(adap);
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if (ret)
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return ret;
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dev_info(dev, "shared I2C bus %u using lines %u (SDA) and %u (SCL) delay=%d\n",
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bus_num, desc_to_gpio(bus->sda), desc_to_gpio(ctx->scl),
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bit_data->udelay);
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}
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return 0;
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}
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static const struct of_device_id gpio_shared_of_match[] = {
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{ .compatible = "i2c-gpio-shared" },
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{}
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};
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MODULE_DEVICE_TABLE(of, gpio_shared_of_match);
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static struct platform_driver gpio_shared_driver = {
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.probe = gpio_shared_probe,
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.driver = {
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.name = "i2c-gpio-shared",
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.of_match_table = gpio_shared_of_match,
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},
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};
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module_platform_driver(gpio_shared_driver);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Markus Stockhausen <markus.stockhausen at gmx.de>");
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MODULE_DESCRIPTION("bitbanging multi I2C driver for shared SCL");
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@ -0,0 +1,41 @@
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From 9d2327c5f1ac63cb14af088a95eba110ab0c473e Mon Sep 17 00:00:00 2001
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From: Markus Stockhausen <markus.stockhausen@gmx.de>
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Date: Wed, 7 May 2025 09:47:24 -0400
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Subject: [PATCH] realtek: add i2c-gpio-shared driver
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Adds the Kconfig and Makefile settings to make the new driver available.
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Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
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---
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drivers/i2c/busses/Kconfig | 9 +++++++++
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drivers/i2c/busses/Makefile | 1 +
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2 files changed, 10 insertions(+)
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--- a/drivers/i2c/busses/Kconfig
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+++ b/drivers/i2c/busses/Kconfig
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@@ -683,6 +683,15 @@ config I2C_GPIO
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This is a very simple bitbanging I2C driver utilizing the
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arch-neutral GPIO API to control the SCL and SDA lines.
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+config I2C_GPIO_SHARED
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+ tristate "multiple GPIO-based bitbanging I2C with shared SCL"
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+ depends on GPIOLIB || COMPILE_TEST
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+ select I2C_ALGOBIT
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+ help
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+ This is an alternative of the I2C GPIO driver for devices with only
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+ few GPIO pins where multiple busses with dedicated SDA lines share
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+ a single SCL line.
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+
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config I2C_GPIO_FAULT_INJECTOR
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bool "GPIO-based fault injector"
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depends on I2C_GPIO
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--- a/drivers/i2c/busses/Makefile
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+++ b/drivers/i2c/busses/Makefile
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@@ -67,6 +67,7 @@ obj-$(CONFIG_I2C_EG20T) += i2c-eg20t.o
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obj-$(CONFIG_I2C_EMEV2) += i2c-emev2.o
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obj-$(CONFIG_I2C_EXYNOS5) += i2c-exynos5.o
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obj-$(CONFIG_I2C_GPIO) += i2c-gpio.o
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+obj-$(CONFIG_I2C_GPIO_SHARED) += i2c-gpio-shared.o
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obj-$(CONFIG_I2C_HIGHLANDER) += i2c-highlander.o
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obj-$(CONFIG_I2C_HISI) += i2c-hisi.o
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obj-$(CONFIG_I2C_HIX5HD2) += i2c-hix5hd2.o
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