Message-ID: <20250915060141.12540-3-clamor95@gmail.com>
Date: Mon, 15 Sep 2025 09:01:38 +0300
From: Svyatoslav Ryhel <clamor95@...il.com>
To: Andi Shyti <andi.shyti@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Peter Rosin <peda@...ntia.se>,
	Michał Mirosław <mirq-linux@...e.qmqm.pl>,
	Svyatoslav Ryhel <clamor95@...il.com>,
	Jonas Schwöbel <jonasschwoebel@...oo.de>
Cc: linux-i2c@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 2/2] i2c: muxes: Add GPIO-detected hotplug I2C

From: Michał Mirosław <mirq-linux@...e.qmqm.pl>

Add support for hot-plugged I2C busses, where some devices on the bus are
hot-pluggable and their presence is indicated by GPIO line.

This feature is used by the ASUS Transformers, Microsoft Surface RT/2 and
maybe more.

Co-developed-by: Ion Agorria <ion@...rria.com>
Signed-off-by: Ion Agorria <ion@...rria.com>
Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
---
 drivers/i2c/muxes/Kconfig            |  11 ++
 drivers/i2c/muxes/Makefile           |   1 +
 drivers/i2c/muxes/i2c-hotplug-gpio.c | 263 +++++++++++++++++++++++++++
 3 files changed, 275 insertions(+)
 create mode 100644 drivers/i2c/muxes/i2c-hotplug-gpio.c

diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 6d2f66810cdc..0e410be5ce55 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -19,6 +19,17 @@ config I2C_ARB_GPIO_CHALLENGE
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-arb-gpio-challenge.
 
+config I2C_HOTPLUG_GPIO
+	tristate "Hot-plugged I2C bus detected by GPIO"
+	depends on GPIOLIB
+	depends on OF
+	help
+	  Say Y here if you want support for hot-plugging I2C devices
+	  with presence detected by GPIO pin value.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called i2c-hotplug-gpio.
+
 config I2C_MUX_GPIO
 	tristate "GPIO-based I2C multiplexer"
 	depends on GPIOLIB
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index 4b24f49515a7..36df41c8cf05 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -6,6 +6,7 @@ obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE)	+= i2c-arb-gpio-challenge.o
 
 obj-$(CONFIG_I2C_DEMUX_PINCTRL)		+= i2c-demux-pinctrl.o
 
+obj-$(CONFIG_I2C_HOTPLUG_GPIO)	+= i2c-hotplug-gpio.o
 obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
 obj-$(CONFIG_I2C_MUX_GPMUX)	+= i2c-mux-gpmux.o
 obj-$(CONFIG_I2C_MUX_LTC4306)	+= i2c-mux-ltc4306.o
diff --git a/drivers/i2c/muxes/i2c-hotplug-gpio.c b/drivers/i2c/muxes/i2c-hotplug-gpio.c
new file mode 100644
index 000000000000..7f56964e285e
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-hotplug-gpio.c
@@ -0,0 +1,263 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+struct i2c_hotplug_priv {
+	struct i2c_adapter adap;
+	struct i2c_adapter *parent;
+	struct device *dev;
+	struct gpio_desc *gpio;
+	int irq;
+};
+
+static inline struct i2c_adapter *i2c_hotplug_parent(struct i2c_adapter *adap)
+{
+	struct i2c_hotplug_priv *priv = container_of(adap, struct i2c_hotplug_priv, adap);
+
+	return priv->parent;
+}
+
+static int i2c_hotplug_master_xfer(struct i2c_adapter *adap,
+				   struct i2c_msg msgs[], int num)
+{
+	struct i2c_adapter *parent = i2c_hotplug_parent(adap);
+
+	return parent->algo->master_xfer(parent, msgs, num);
+}
+
+static int i2c_hotplug_smbus_xfer(struct i2c_adapter *adap, u16 addr,
+				  unsigned short flags, char read_write,
+				  u8 command, int protocol,
+				  union i2c_smbus_data *data)
+{
+	struct i2c_adapter *parent = i2c_hotplug_parent(adap);
+
+	return parent->algo->smbus_xfer(parent, addr, flags, read_write,
+					command, protocol, data);
+}
+
+static u32 i2c_hotplug_functionality(struct i2c_adapter *adap)
+{
+	u32 parent_func = i2c_get_functionality(i2c_hotplug_parent(adap));
+
+	return parent_func & ~I2C_FUNC_SLAVE;
+}
+
+static const struct i2c_algorithm i2c_hotplug_algo_i2c = {
+	.master_xfer = i2c_hotplug_master_xfer,
+	.functionality = i2c_hotplug_functionality,
+};
+
+static const struct i2c_algorithm i2c_hotplug_algo_smbus = {
+	.smbus_xfer = i2c_hotplug_smbus_xfer,
+	.functionality = i2c_hotplug_functionality,
+};
+
+static const struct i2c_algorithm i2c_hotplug_algo_both = {
+	.master_xfer = i2c_hotplug_master_xfer,
+	.smbus_xfer = i2c_hotplug_smbus_xfer,
+	.functionality = i2c_hotplug_functionality,
+};
+
+static const struct i2c_algorithm *const i2c_hotplug_algo[2][2] = {
+	/* non-I2C */
+	{ NULL, &i2c_hotplug_algo_smbus },
+	/* I2C */
+	{ &i2c_hotplug_algo_i2c, &i2c_hotplug_algo_both }
+};
+
+static void i2c_hotplug_lock_bus(struct i2c_adapter *adap, unsigned int flags)
+{
+	i2c_lock_bus(i2c_hotplug_parent(adap), flags);
+}
+
+static int i2c_hotplug_trylock_bus(struct i2c_adapter *adap,
+				   unsigned int flags)
+{
+	return i2c_trylock_bus(i2c_hotplug_parent(adap), flags);
+}
+
+static void i2c_hotplug_unlock_bus(struct i2c_adapter *adap,
+				   unsigned int flags)
+{
+	i2c_unlock_bus(i2c_hotplug_parent(adap), flags);
+}
+
+static const struct i2c_lock_operations i2c_hotplug_lock_ops = {
+	.lock_bus = i2c_hotplug_lock_bus,
+	.trylock_bus = i2c_hotplug_trylock_bus,
+	.unlock_bus = i2c_hotplug_unlock_bus,
+};
+
+static int i2c_hotplug_recover_bus(struct i2c_adapter *adap)
+{
+	return i2c_recover_bus(i2c_hotplug_parent(adap));
+}
+
+static struct i2c_bus_recovery_info i2c_hotplug_recovery_info = {
+	.recover_bus = i2c_hotplug_recover_bus,
+};
+
+static int i2c_hotplug_activate(struct i2c_hotplug_priv *priv)
+{
+	int ret;
+
+	if (priv->adap.algo_data)
+		return 0;
+
+	/*
+	 * Store the dev data in adapter dev, since
+	 * previous i2c_del_adapter might have wiped it.
+	 */
+	priv->adap.dev.parent = priv->dev;
+	priv->adap.dev.of_node = priv->dev->of_node;
+
+	dev_dbg(priv->adap.dev.parent, "connection detected");
+
+	ret = i2c_add_adapter(&priv->adap);
+	if (!ret)
+		priv->adap.algo_data = (void *)1;
+
+	return ret;
+}
+
+static void i2c_hotplug_deactivate(struct i2c_hotplug_priv *priv)
+{
+	if (!priv->adap.algo_data)
+		return;
+
+	dev_dbg(priv->adap.dev.parent, "disconnection detected");
+
+	i2c_del_adapter(&priv->adap);
+	priv->adap.algo_data = NULL;
+}
+
+static irqreturn_t i2c_hotplug_interrupt(int irq, void *dev_id)
+{
+	struct i2c_hotplug_priv *priv = dev_id;
+
+	/* debounce */
+	msleep(20);
+
+	if (gpiod_get_value_cansleep(priv->gpio))
+		i2c_hotplug_activate(priv);
+	else
+		i2c_hotplug_deactivate(priv);
+
+	return IRQ_HANDLED;
+}
+
+static void wrap_i2c_put_adapter(void *adapter)
+{
+	i2c_put_adapter(adapter);
+}
+
+static void wrap_i2c_hotplug_deactivate(void *priv)
+{
+	i2c_hotplug_deactivate(priv);
+}
+
+static int i2c_hotplug_gpio_probe(struct platform_device *pdev)
+{
+	struct device_node *parent_np;
+	struct i2c_adapter *parent;
+	struct i2c_hotplug_priv *priv;
+	bool is_i2c, is_smbus;
+	int err;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, priv);
+	priv->dev = &pdev->dev;
+
+	parent_np = of_parse_phandle(pdev->dev.of_node, "i2c-parent", 0);
+	if (IS_ERR(parent_np))
+		return dev_err_probe(&pdev->dev, PTR_ERR(parent_np),
+				     "cannot parse i2c-parent\n");
+
+	parent = of_find_i2c_adapter_by_node(parent_np);
+	of_node_put(parent_np);
+	if (IS_ERR(parent))
+		return dev_err_probe(&pdev->dev, PTR_ERR(parent),
+				     "failed to get parent I2C adapter\n");
+	priv->parent = parent;
+
+	err = devm_add_action_or_reset(&pdev->dev, wrap_i2c_put_adapter,
+				       parent);
+	if (err)
+		return err;
+
+	priv->gpio = devm_gpiod_get(&pdev->dev, "detect", GPIOD_IN);
+	if (IS_ERR(priv->gpio))
+		return dev_err_probe(&pdev->dev, PTR_ERR(priv->gpio),
+				     "failed to get detect GPIO\n");
+
+	is_i2c = parent->algo->master_xfer;
+	is_smbus = parent->algo->smbus_xfer;
+
+	snprintf(priv->adap.name, sizeof(priv->adap.name),
+		 "i2c-hotplug (master i2c-%d)", i2c_adapter_id(parent));
+	priv->adap.owner = THIS_MODULE;
+	priv->adap.algo = i2c_hotplug_algo[is_i2c][is_smbus];
+	priv->adap.algo_data = NULL;
+	priv->adap.lock_ops = &i2c_hotplug_lock_ops;
+	priv->adap.class = parent->class;
+	priv->adap.retries = parent->retries;
+	priv->adap.timeout = parent->timeout;
+	priv->adap.quirks = parent->quirks;
+	if (parent->bus_recovery_info)
+		/* .bus_recovery_info is not const, but won't be modified */
+		priv->adap.bus_recovery_info = (void *)&i2c_hotplug_recovery_info;
+
+	if (!priv->adap.algo)
+		return -EINVAL;
+
+	err = devm_add_action_or_reset(&pdev->dev, wrap_i2c_hotplug_deactivate, priv);
+	if (err)
+		return err;
+
+	priv->irq = platform_get_irq(pdev, 0);
+	if (priv->irq < 0)
+		return dev_err_probe(&pdev->dev, priv->irq,
+				     "failed to get IRQ %d\n", priv->irq);
+
+	err = devm_request_threaded_irq(&pdev->dev, priv->irq, NULL,
+					i2c_hotplug_interrupt,
+					IRQF_ONESHOT | IRQF_SHARED,
+					"i2c-hotplug", priv);
+	if (err)
+		return dev_err_probe(&pdev->dev, err,
+				     "failed to register IRQ %d\n", priv->irq);
+
+	irq_wake_thread(priv->irq, priv);
+
+	return 0;
+}
+
+static const struct of_device_id i2c_hotplug_gpio_of_match[] = {
+	{ .compatible = "i2c-hotplug-gpio" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, i2c_hotplug_gpio_of_match);
+
+static struct platform_driver i2c_hotplug_gpio_driver = {
+	.driver	= {
+		.name = "i2c-hotplug-gpio",
+		.of_match_table = i2c_hotplug_gpio_of_match,
+	},
+	.probe = i2c_hotplug_gpio_probe,
+};
+
+module_platform_driver(i2c_hotplug_gpio_driver);
+
+MODULE_DESCRIPTION("Hot-plugged I2C bus detected by GPIO");
+MODULE_AUTHOR("Michał Mirosław <mirq-linux@...e.qmqm.pl>");
+MODULE_LICENSE("GPL");
-- 
2.48.1

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