[PATCH v3 2/2] i2c: Add GPIO-based hotplug gate

Svyatoslav Ryhel
2023-07-29T16:09:34Z

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

Implement driver for hot-plugged I2C busses, where some devices on
a bus are hot-pluggable and their presence is indicated by GPIO line.

This feature is mainly used by the ASUS Transformers family. The
Transformers have a connector that's used for USB, charging or for
attaching a dock-keyboard (which also has a battery and a touchpad).
This connector probably (can't be verified since no datasheets or
special equipment is available) has an I2C bus lines and a "detect"
line (pulled low on the dock side) among the pins. I guess there
is either no additional chip or a transparent bridge/buffer chip,
but nothing that could be controlled by software. For DT this setup
could be modelled like an I2C gate or 2-port mux with enable joining
two I2C buses (one "closer" to the CPU as a parent).

Co-developed-by: Ion Agorria <ion@agorria.com>
Signed-off-by: Ion Agorria <ion@agorria.com>
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
---
drivers/i2c/Kconfig | 11 ++
drivers/i2c/Makefile | 1 +
drivers/i2c/i2c-hotplug-gpio.c | 266 +++++++++++++++++++++++++++++++++
3 files changed, 278 insertions(+)
create mode 100644 drivers/i2c/i2c-hotplug-gpio.c

diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 438905e2a1d0..3e3f7675ea4a 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -98,6 +98,17 @@ config I2C_SMBUS
source "drivers/i2c/algos/Kconfig"
source "drivers/i2c/busses/Kconfig"

+config I2C_HOTPLUG_GPIO
+ tristate "Hot-plugged I2C bus detected by GPIO"
+ depends on GPIOLIB
+ depends on OF
+ help
+ If you say yes to this option, support will be included 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_STUB
tristate "I2C/SMBus Test Stub"
depends on m
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index c1d493dc9bac..9fd44310835a 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_I2C_SMBUS) += i2c-smbus.o
obj-$(CONFIG_I2C_CHARDEV) += i2c-dev.o
obj-$(CONFIG_I2C_MUX) += i2c-mux.o
obj-y += algos/ busses/ muxes/
+obj-$(CONFIG_I2C_HOTPLUG_GPIO) += i2c-hotplug-gpio.o
obj-$(CONFIG_I2C_STUB) += i2c-stub.o
obj-$(CONFIG_I2C_SLAVE_EEPROM) += i2c-slave-eeprom.o
obj-$(CONFIG_I2C_SLAVE_TESTUNIT) += i2c-slave-testunit.o
diff --git a/drivers/i2c/i2c-hotplug-gpio.c b/drivers/i2c/i2c-hotplug-gpio.c
new file mode 100644
index 000000000000..18c2d7f44d29
--- /dev/null
+++ b/drivers/i2c/i2c-hotplug-gpio.c
@@ -0,0 +1,266 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * I2C hotplug gate controlled by GPIO
+ */
+
+#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 devm_i2c_put_adapter(void *adapter)
+{
+ i2c_put_adapter(adapter);
+}
+
+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 ret;
+
+ 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;
+
+ ret = devm_add_action_or_reset(&pdev->dev, devm_i2c_put_adapter,
+ parent);
+ if (ret)
+ return ret;
+
+ 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)
+ priv->adap.bus_recovery_info = &i2c_hotplug_recovery_info;
+
+ if (!priv->adap.algo)
+ return -EINVAL;
+
+ 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);
+
+ ret = devm_request_threaded_irq(&pdev->dev, priv->irq, NULL,
+ i2c_hotplug_interrupt,
+ IRQF_ONESHOT | IRQF_SHARED,
+ "i2c-hotplug", priv);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "failed to register IRQ %d\n", priv->irq);
+
+ irq_wake_thread(priv->irq, priv);
+
+ return 0;
+}
+
+static int i2c_hotplug_gpio_remove(struct platform_device *pdev)
+{
+ struct i2c_hotplug_priv *priv = platform_get_drvdata(pdev);
+
+ i2c_hotplug_deactivate(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 = {
+ .probe = i2c_hotplug_gpio_probe,
+ .remove = i2c_hotplug_gpio_remove,
+ .driver = {
+ .name = "i2c-hotplug-gpio",
+ .of_match_table = i2c_hotplug_gpio_of_match,
+ },
+};
+
+module_platform_driver(i2c_hotplug_gpio_driver);
+
+MODULE_DESCRIPTION("Hot-plugged I2C bus detected by GPIO");
+MODULE_AUTHOR("Michał Mirosław <mirq-linux@rere.qmqm.pl>");
+MODULE_LICENSE("GPL");
--
2.39.2