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realtek: add new i2c-gpio-shared driver for shared SCL lines

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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 2025-06-13 04:29:52 -04:00 committed by Robert Marko
parent 2f85dc277b
commit acd7ecc9ed
3 changed files with 271 additions and 0 deletions
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51
target/linux/realtek/files-6.12/Documentation/devicetree/bindings/i2c/i2c-gpio-shared.yaml Normal file
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# SPDX-License-Identifier: GPL-2.0
%YAML 1.2
---
$id: http://devicetree.org/schemas/i2c/i2c-gpio-shared.yaml#
$schema: http://devicetree.org/meta-schemas/core.yaml#
title: mulitple GPIO bitbanged I2C busses with shared SCL
maintainers:
- Markus Stockhausen <markus.stockhausen@gmx.de>
allOf:
- $ref: /schemas/i2c/i2c-controller.yaml#
properties:
compatible:
items:
- const: i2c-gpio-shared
scl-gpios:
description:
gpio used for the shared scl signal, this should be flagged as
active high using open drain with (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN)
from <dt-bindings/gpio/gpio.h> since the signal is by definition
open drain.
maxItems: 1
examples:
- |
#include <dt-bindings/gpio/gpio.h>
i2c-gpio-shared {
compatible = "i2c-gpio-shared";
scl-gpios = <&gpio1 31 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
#address-cells = <1>;
#size-cells = <0>;
i2c0: i2c@0 {
sda-gpios = <&gpio1 6 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
i2c-gpio,delay-us = <2>;
};
i2c1: i2c@1 {
sda-gpios = <&gpio1 7 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
i2c-gpio,delay-us = <2>;
};
};
required:
- compatible
- scl-gpios

179
target/linux/realtek/files-6.12/drivers/i2c/busses/i2c-gpio-shared.c Normal file
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// SPDX-License-Identifier: GPL-2.0
/*
* Bitbanging driver for multiple I2C busses with shared SCL pin using the GPIO API
* Copyright (c) 2025 Markus Stockhausen <markus.stockhausen at gmx.de>
*/
#include <linux/i2c-algo-bit.h>
#include <linux/gpio/consumer.h>
#include <linux/mod_devicetable.h>
#include <linux/mutex.h>
#include <linux/platform_device.h>
struct gpio_shared_ctx;
struct gpio_shared_bus {
int num;
struct gpio_desc *sda;
struct i2c_adapter adap;
struct i2c_algo_bit_data bit_data;
struct gpio_shared_ctx *ctx;
};
#define GPIO_SHARED_MAX_BUS 4
struct gpio_shared_ctx {
struct device *dev;
struct gpio_desc *scl;
struct mutex lock;
struct gpio_shared_bus bus[GPIO_SHARED_MAX_BUS];
};
static void gpio_shared_setsda(void *data, int state)
{
struct gpio_shared_bus *bus = data;
gpiod_set_value_cansleep(bus->sda, state);
}
static void gpio_shared_setscl(void *data, int state)
{
struct gpio_shared_bus *bus = data;
struct gpio_shared_ctx *ctx = bus->ctx;
gpiod_set_value_cansleep(ctx->scl, state);
}
static int gpio_shared_getsda(void *data)
{
struct gpio_shared_bus *bus = data;
return gpiod_get_value_cansleep(bus->sda);
}
static int gpio_shared_getscl(void *data)
{
struct gpio_shared_bus *bus = data;
struct gpio_shared_ctx *ctx = bus->ctx;
return gpiod_get_value_cansleep(ctx->scl);
}
static int gpio_shared_pre_xfer(struct i2c_adapter *adap)
{
struct gpio_shared_bus *bus = container_of(adap, typeof(*bus), adap);
struct gpio_shared_ctx *ctx = bus->ctx;
mutex_lock(&ctx->lock);
dev_dbg(ctx->dev, "lock before transfer to bus %d\n", bus->num);
return 0;
}
static void gpio_shared_post_xfer(struct i2c_adapter *adap)
{
struct gpio_shared_bus *bus = container_of(adap, typeof(*bus), adap);
struct gpio_shared_ctx *ctx = bus->ctx;
dev_dbg(ctx->dev, "unlock after transfer to bus %d\n", bus->num);
mutex_unlock(&ctx->lock);
}
static int gpio_shared_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct fwnode_handle *child;
struct gpio_shared_ctx *ctx;
int msecs, ret, bus_num = -1;
ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return -ENOMEM;
ctx->dev = dev;
mutex_init(&ctx->lock);
ctx->scl = devm_gpiod_get(dev, "scl", GPIOD_OUT_HIGH_OPEN_DRAIN);
if (IS_ERR(ctx->scl))
return dev_err_probe(dev, PTR_ERR(ctx->scl), "shared SCL node not found\n");
if (device_get_child_node_count(dev) >= GPIO_SHARED_MAX_BUS)
return dev_err_probe(dev, -EINVAL, "Too many channels\n");
device_for_each_child_node(dev, child) {
struct gpio_shared_bus *bus = &ctx->bus[++bus_num];
struct i2c_adapter *adap = &bus->adap;
struct i2c_algo_bit_data *bit_data = &bus->bit_data;
bus->sda = devm_fwnode_gpiod_get(dev, child, "sda", GPIOD_OUT_HIGH_OPEN_DRAIN,
fwnode_get_name(child));
if (IS_ERR(bus->sda)) {
fwnode_handle_put(child);
dev_err(dev, "SDA node for bus %d not found\n", bus_num);
continue;
}
bus->num = bus_num;
bus->ctx = ctx;
bit_data->data = bus;
bit_data->setsda = gpio_shared_setsda;
bit_data->setscl = gpio_shared_setscl;
bit_data->pre_xfer = gpio_shared_pre_xfer;
bit_data->post_xfer = gpio_shared_post_xfer;
if (fwnode_property_read_u32(child, "i2c-gpio,delay-us", &bit_data->udelay))
bit_data->udelay = 5;
if (!fwnode_property_read_bool(child, "i2c-gpio,sda-output-only"))
bit_data->getsda = gpio_shared_getsda;
if (!device_property_read_bool(dev, "i2c-gpio,scl-output-only"))
bit_data->getscl = gpio_shared_getscl;
if (!device_property_read_u32(dev, "i2c-gpio,timeout-ms", &msecs))
bit_data->timeout = msecs_to_jiffies(msecs);
else
bit_data->timeout = HZ / 10; /* 100ms */
if (gpiod_cansleep(bus->sda) || gpiod_cansleep(ctx->scl))
dev_warn(dev, "Slow GPIO pins might wreak havoc into I2C/SMBus bus timing");
else
bit_data->can_do_atomic = true;
adap->owner = THIS_MODULE;
strscpy(adap->name, KBUILD_MODNAME, sizeof(adap->name));
adap->dev.parent = dev;
device_set_node(&adap->dev, child);
adap->algo_data = &bus->bit_data;
adap->class = I2C_CLASS_HWMON;
ret = i2c_bit_add_bus(adap);
if (ret)
return ret;
dev_info(dev, "shared I2C bus %u using lines %u (SDA) and %u (SCL) delay=%d\n",
bus_num, desc_to_gpio(bus->sda), desc_to_gpio(ctx->scl),
bit_data->udelay);
}
return 0;
}
static const struct of_device_id gpio_shared_of_match[] = {
{ .compatible = "i2c-gpio-shared" },
{}
};
MODULE_DEVICE_TABLE(of, gpio_shared_of_match);
static struct platform_driver gpio_shared_driver = {
.probe = gpio_shared_probe,
.driver = {
.name = "i2c-gpio-shared",
.of_match_table = gpio_shared_of_match,
},
};
module_platform_driver(gpio_shared_driver);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Markus Stockhausen <markus.stockhausen at gmx.de>");
MODULE_DESCRIPTION("bitbanging multi I2C driver for shared SCL");

41
target/linux/realtek/patches-6.12/805-add-i2c-gpio-shared-driver.patch Normal file
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From 9d2327c5f1ac63cb14af088a95eba110ab0c473e Mon Sep 17 00:00:00 2001
From: Markus Stockhausen <markus.stockhausen@gmx.de>
Date: Wed, 7 May 2025 09:47:24 -0400
Subject: [PATCH] realtek: add i2c-gpio-shared driver
Adds the Kconfig and Makefile settings to make the new driver available.
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
---
drivers/i2c/busses/Kconfig | 9 +++++++++
drivers/i2c/busses/Makefile | 1 +
2 files changed, 10 insertions(+)
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -683,6 +683,15 @@ config I2C_GPIO
This is a very simple bitbanging I2C driver utilizing the
arch-neutral GPIO API to control the SCL and SDA lines.
+config I2C_GPIO_SHARED
+ tristate "multiple GPIO-based bitbanging I2C with shared SCL"
+ depends on GPIOLIB || COMPILE_TEST
+ select I2C_ALGOBIT
+ help
+ This is an alternative of the I2C GPIO driver for devices with only
+ few GPIO pins where multiple busses with dedicated SDA lines share
+ a single SCL line.
+
config I2C_GPIO_FAULT_INJECTOR
bool "GPIO-based fault injector"
depends on I2C_GPIO
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -67,6 +67,7 @@ obj-$(CONFIG_I2C_EG20T) += i2c-eg20t.o
obj-$(CONFIG_I2C_EMEV2) += i2c-emev2.o
obj-$(CONFIG_I2C_EXYNOS5) += i2c-exynos5.o
obj-$(CONFIG_I2C_GPIO) += i2c-gpio.o
+obj-$(CONFIG_I2C_GPIO_SHARED) += i2c-gpio-shared.o
obj-$(CONFIG_I2C_HIGHLANDER) += i2c-highlander.o
obj-$(CONFIG_I2C_HISI) += i2c-hisi.o
obj-$(CONFIG_I2C_HIX5HD2) += i2c-hix5hd2.o