i2c: muxes: add support for tsd,mule-i2c multiplexer

Theobroma Systems Mule is an MCU that emulates a set of I2C devices,
among which an amc6821 and devices that are reachable through an I2C-mux.
The devices on the mux can be selected by writing the appropriate device
number to an I2C config register (amc6821 reg 0xff).

This driver is expected to be probed as a platform device with amc6821
as its parent i2c device.

Add support for the mule-i2c-mux platform driver. The amc6821 driver
support for the mux will be added in a later commit.

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Farouk Bouabid <farouk.bouabid@cherry.de>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

drivers/i2c/muxes/Kconfig

@@ -119,4 +119,20 @@ config I2C_MUX_MLXCPLD
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-mux-mlxcpld.
 
+config I2C_MUX_MULE
+	tristate "Theobroma Systems Mule I2C device multiplexer"
+	depends on OF && SENSORS_AMC6821
+	help
+	  Mule is an MCU that emulates a set of I2C devices, among which
+	  devices that are reachable through an I2C-mux. The devices on the mux
+	  can be selected by writing the appropriate device number to an I2C
+	  configuration register.
+
+	  If you say yes to this option, support will be included for a
+	  Theobroma Systems Mule I2C multiplexer. This driver provides access to
+	  I2C devices connected on this mux.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called i2c-mux-mule.
+
 endmenu

drivers/i2c/muxes/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
 obj-$(CONFIG_I2C_MUX_GPMUX)	+= i2c-mux-gpmux.o
 obj-$(CONFIG_I2C_MUX_LTC4306)	+= i2c-mux-ltc4306.o
 obj-$(CONFIG_I2C_MUX_MLXCPLD)	+= i2c-mux-mlxcpld.o
+obj-$(CONFIG_I2C_MUX_MULE)	+= i2c-mux-mule.o
 obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
 obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
 obj-$(CONFIG_I2C_MUX_PINCTRL)	+= i2c-mux-pinctrl.o

drivers/i2c/muxes/i2c-mux-mule.c

@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Theobroma Systems Mule I2C device multiplexer
+ *
+ * Copyright (C) 2024 Theobroma Systems Design und Consulting GmbH
+ */
+
+#include <linux/i2c-mux.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+
+#define MULE_I2C_MUX_CONFIG_REG  0xff
+#define MULE_I2C_MUX_DEFAULT_DEV 0x0
+
+struct mule_i2c_reg_mux {
+	struct regmap *regmap;
+};
+
+static int mule_i2c_mux_select(struct i2c_mux_core *muxc, u32 dev)
+{
+	struct mule_i2c_reg_mux *mux = muxc->priv;
+
+	return regmap_write(mux->regmap, MULE_I2C_MUX_CONFIG_REG, dev);
+}
+
+static int mule_i2c_mux_deselect(struct i2c_mux_core *muxc, u32 dev)
+{
+	return mule_i2c_mux_select(muxc, MULE_I2C_MUX_DEFAULT_DEV);
+}
+
+static void mule_i2c_mux_remove(void *data)
+{
+	struct i2c_mux_core *muxc = data;
+
+	i2c_mux_del_adapters(muxc);
+
+	mule_i2c_mux_deselect(muxc, MULE_I2C_MUX_DEFAULT_DEV);
+}
+
+static int mule_i2c_mux_probe(struct platform_device *pdev)
+{
+	struct device *mux_dev = &pdev->dev;
+	struct mule_i2c_reg_mux *priv;
+	struct i2c_client *client;
+	struct i2c_mux_core *muxc;
+	struct device_node *dev;
+	unsigned int readback;
+	int ndev, ret;
+	bool old_fw;
+
+	/* Count devices on the mux */
+	ndev = of_get_child_count(mux_dev->of_node);
+	dev_dbg(mux_dev, "%d devices on the mux\n", ndev);
+
+	client = to_i2c_client(mux_dev->parent);
+
+	muxc = i2c_mux_alloc(client->adapter, mux_dev, ndev, sizeof(*priv),
+			     I2C_MUX_LOCKED, mule_i2c_mux_select, mule_i2c_mux_deselect);
+	if (!muxc)
+		return -ENOMEM;
+
+	priv = i2c_mux_priv(muxc);
+
+	priv->regmap = dev_get_regmap(mux_dev->parent, NULL);
+	if (IS_ERR(priv->regmap))
+		return dev_err_probe(mux_dev, PTR_ERR(priv->regmap),
+				     "No parent i2c register map\n");
+
+	platform_set_drvdata(pdev, muxc);
+
+	/*
+	 * MULE_I2C_MUX_DEFAULT_DEV is guaranteed to exist on all old and new
+	 * mule fw. Mule fw without mux support will accept write ops to the
+	 * config register, but readback returns 0xff (register not updated).
+	 */
+	ret = mule_i2c_mux_select(muxc, MULE_I2C_MUX_DEFAULT_DEV);
+	if (ret)
+		return dev_err_probe(mux_dev, ret,
+				     "Failed to write config register\n");
+
+	ret = regmap_read(priv->regmap, MULE_I2C_MUX_CONFIG_REG, &readback);
+	if (ret)
+		return dev_err_probe(mux_dev, ret,
+				     "Failed to read config register\n");
+
+	old_fw = (readback != MULE_I2C_MUX_DEFAULT_DEV);
+
+	ret = devm_add_action_or_reset(mux_dev, mule_i2c_mux_remove, muxc);
+	if (ret)
+		return dev_err_probe(mux_dev, ret,
+				     "Failed to register mux remove\n");
+
+	/* Create device adapters */
+	for_each_child_of_node(mux_dev->of_node, dev) {
+		u32 reg;
+
+		ret = of_property_read_u32(dev, "reg", &reg);
+		if (ret)
+			return dev_err_probe(mux_dev, ret,
+					     "No reg property found for %s\n",
+					     of_node_full_name(dev));
+
+		if (old_fw && reg != 0) {
+			dev_warn(mux_dev,
+				 "Mux is not supported, please update Mule FW\n");
+			continue;
+		}
+
+		ret = mule_i2c_mux_select(muxc, reg);
+		if (ret) {
+			dev_warn(mux_dev,
+				 "Device %d not supported, please update Mule FW\n", reg);
+			continue;
+		}
+
+		ret = i2c_mux_add_adapter(muxc, 0, reg);
+		if (ret)
+			return ret;
+	}
+
+	mule_i2c_mux_deselect(muxc, MULE_I2C_MUX_DEFAULT_DEV);
+
+	return 0;
+}
+
+static const struct of_device_id mule_i2c_mux_of_match[] = {
+	{ .compatible = "tsd,mule-i2c-mux", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mule_i2c_mux_of_match);
+
+static struct platform_driver mule_i2c_mux_driver = {
+	.driver = {
+		.name	= "mule-i2c-mux",
+		.of_match_table = mule_i2c_mux_of_match,
+	},
+	.probe		= mule_i2c_mux_probe,
+};
+
+module_platform_driver(mule_i2c_mux_driver);
+
+MODULE_AUTHOR("Farouk Bouabid <farouk.bouabid@cherry.de>");
+MODULE_DESCRIPTION("I2C mux driver for Theobroma Systems Mule");
+MODULE_LICENSE("GPL");