[PATCH 3/7] i2c: muxes: add support for mule i2c multiplexer

[Farouk Bouabid]

Mule is an mcu that emulates a set of i2c devices which are reacheable
through an i2c-mux.

The emulated devices share a single i2c address with the mux itself where
the requested register is what determines which logic is executed (mux or
device):

1- The devices on the mux can be selected (mux function) by writing the
appropriate device number to an i2c config register (0xff) that is not
used by any device logic.

2- Any access to a register other than the config register will be
handled by the previously selected device.

Signed-off-by: Farouk Bouabid <farouk.bouabid@xxxxxxxxxxxxxxxxxxxxx>
---
 drivers/i2c/muxes/Kconfig        |  11 +++
 drivers/i2c/muxes/Makefile       |   1 +
 drivers/i2c/muxes/i2c-mux-mule.c | 157 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 169 insertions(+)

diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index db1b9057612a..593a20a6ac51 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -119,4 +119,15 @@ 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 "Mule I2C device multiplexer"
+	depends on OF
+	help
+	  If you say yes to this option, support will be included for a
+	  Mule I2C device multiplexer. This driver provides access to
+	  I2C devices connected on the Mule I2C mux.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called i2c-mux-mule.
+
 endmenu
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index 6d9d865e8518..4b24f49515a7 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/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
diff --git a/drivers/i2c/muxes/i2c-mux-mule.c b/drivers/i2c/muxes/i2c-mux-mule.c
new file mode 100644
index 000000000000..da2a9526522e
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-mux-mule.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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/property.h>
+#include <linux/regmap.h>
+
+#define MUX_CONFIG_REG	0xff
+#define MUX_DEFAULT_DEV	0x0
+
+struct mule_i2c_reg_mux {
+	struct regmap *regmap;
+};
+
+static const struct regmap_config mule_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+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 inline int __mux_select(struct regmap *regmap, u32 dev)
+{
+	return regmap_write(regmap, MUX_CONFIG_REG, dev);
+}
+
+static int mux_select(struct i2c_mux_core *muxc, u32 dev)
+{
+	struct mule_i2c_reg_mux *mux = muxc->priv;
+
+	return __mux_select(mux->regmap, dev);
+}
+
+static int mux_deselect(struct i2c_mux_core *muxc, u32 dev)
+{
+	return mux_select(muxc, MUX_DEFAULT_DEV);
+}
+
+static void mux_remove(void *data)
+{
+	struct i2c_mux_core *muxc = data;
+
+	i2c_mux_del_adapters(muxc);
+
+	mux_deselect(muxc, MUX_DEFAULT_DEV);
+}
+
+static int mule_i2c_mux_probe(struct i2c_client *client)
+{
+	struct i2c_adapter *adap = client->adapter;
+	struct mule_i2c_reg_mux *priv;
+	struct i2c_mux_core *muxc;
+	struct device_node *dev;
+	unsigned int readback;
+	bool old_fw;
+	int ndev, ret;
+
+	/* Count devices on the mux */
+	ndev = of_get_child_count(client->dev.of_node);
+	dev_dbg(&client->dev, "%u devices on the mux\n", ndev);
+
+	muxc = i2c_mux_alloc(adap, &client->dev,
+						 ndev, sizeof(*priv),
+						 I2C_MUX_LOCKED,
+						 mux_select, mux_deselect);
+	if (!muxc)
+		return -ENOMEM;
+
+	muxc->share_addr_with_children = 1;
+	priv = i2c_mux_priv(muxc);
+
+	priv->regmap = devm_regmap_init_i2c(client, &mule_regmap_config);
+	if (IS_ERR(priv->regmap))
+		return dev_err_probe(&client->dev, PTR_ERR(priv->regmap),
+							 "Failed to allocate i2c register map\n");
+
+	i2c_set_clientdata(client, muxc);
+
+	/*
+	 * Mux 0 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 = mux_select(muxc, 0);
+	if (ret)
+		return ret;
+
+	ret = regmap_read(priv->regmap, MUX_CONFIG_REG, &readback);
+	if (ret)
+		return ret;
+
+	old_fw = (readback == 0);
+
+	ret = devm_add_action_or_reset(&client->dev, mux_remove, muxc);
+	if (ret)
+		return ret;
+
+	/* Create device adapters */
+	for_each_child_of_node(client->dev.of_node, dev) {
+		u32 reg;
+
+		ret = of_property_read_u32(dev, "reg", &reg);
+		if (ret) {
+			dev_err(&client->dev, "No reg property found for %s: %d\n",
+					of_node_full_name(dev), ret);
+			return ret;
+		}
+
+		if (!old_fw && reg != 0) {
+			dev_warn(&client->dev,
+					 "Mux %d not supported, please update Mule FW\n", reg);
+			continue;
+		}
+
+		ret = mux_select(muxc, reg);
+		if (ret) {
+			dev_warn(&client->dev,
+					 "Mux %d not supported, please update Mule FW\n", reg);
+			continue;
+		}
+
+		ret = i2c_mux_add_adapter(muxc, 0, reg, 0);
+		if (ret) {
+			dev_err(&client->dev, "Failed to add i2c mux adapter %d: %d\n", reg, ret);
+			return ret;
+		}
+	}
+
+	mux_deselect(muxc, MUX_DEFAULT_DEV);
+
+	return 0;
+}
+
+static struct i2c_driver mule_i2c_mux_driver = {
+	.driver		= {
+		.name	= "mule-i2c-mux",
+		.of_match_table = mule_i2c_mux_of_match,
+	},
+	.probe		= mule_i2c_mux_probe,
+};
+
+module_i2c_driver(mule_i2c_mux_driver);
+
+MODULE_AUTHOR("Farouk Bouabid <farouk.bouabid@xxxxxxxxxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("I2C mux driver for Mule");
+MODULE_LICENSE("GPL");

-- 
2.34.1