This driver supports I2C adapter functionality for NCT6694 MFD
device based on USB interface, each I2C controller use default
baudrate(100K).

Signed-off-by: Ming Yu <tmyu0@nuvoton.com>
---
 MAINTAINERS                      |   1 +
 drivers/i2c/busses/Kconfig       |  10 ++
 drivers/i2c/busses/Makefile      |   1 +
 drivers/i2c/busses/i2c-nct6694.c | 152 +++++++++++++++++++++++++++++++
 4 files changed, 164 insertions(+)
 create mode 100644 drivers/i2c/busses/i2c-nct6694.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 6688c5c470b7..a190f2b08fa3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16546,6 +16546,7 @@ M:	Ming Yu <tmyu0@nuvoton.com>
 L:	linux-kernel@vger.kernel.org
 S:	Supported
 F:	drivers/gpio/gpio-nct6694.c
+F:	drivers/i2c/busses/i2c-nct6694.c
 F:	drivers/mfd/nct6694.c
 F:	include/linux/mfd/nct6694.h
 
diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 4977abcd7c46..1962cf1e71f9 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -1325,6 +1325,16 @@ config I2C_LJCA
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-ljca.
 
+config I2C_NCT6694
+	tristate "Nuvoton NCT6694 I2C adapter support"
+	depends on MFD_NCT6694
+	help
+	  If you say yes to this option, support will be included for Nuvoton
+	  NCT6694, a USB to I2C interface.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called i2c-nct6694.
+
 config I2C_CP2615
 	tristate "Silicon Labs CP2615 USB sound card and I2C adapter"
 	depends on USB
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index a6bcbf2febcf..6d2fd8e56569 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -135,6 +135,7 @@ obj-$(CONFIG_I2C_GXP)		+= i2c-gxp.o
 obj-$(CONFIG_I2C_DIOLAN_U2C)	+= i2c-diolan-u2c.o
 obj-$(CONFIG_I2C_DLN2)		+= i2c-dln2.o
 obj-$(CONFIG_I2C_LJCA)		+= i2c-ljca.o
+obj-$(CONFIG_I2C_NCT6694)	+= i2c-nct6694.o
 obj-$(CONFIG_I2C_CP2615) += i2c-cp2615.o
 obj-$(CONFIG_I2C_PARPORT)	+= i2c-parport.o
 obj-$(CONFIG_I2C_PCI1XXXX)	+= i2c-mchp-pci1xxxx.o
diff --git a/drivers/i2c/busses/i2c-nct6694.c b/drivers/i2c/busses/i2c-nct6694.c
new file mode 100644
index 000000000000..2a5e0629f860
--- /dev/null
+++ b/drivers/i2c/busses/i2c-nct6694.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Nuvoton NCT6694 I2C adapter driver based on USB interface.
+ *
+ * Copyright (C) 2024 Nuvoton Technology Corp.
+ */
+
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/nct6694.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+/* Host interface */
+#define NCT6694_I2C_MOD		0x03
+
+/* Message Channel*/
+/* Command 00h */
+#define NCT6694_I2C_CMD0_OFFSET	0x0000	/* OFFSET = SEL|CMD */
+#define NCT6694_I2C_CMD0_LEN	0x90
+
+enum i2c_baudrate {
+	I2C_BR_25K = 0,
+	I2C_BR_50K,
+	I2C_BR_100K,
+	I2C_BR_200K,
+	I2C_BR_400K,
+	I2C_BR_800K,
+	I2C_BR_1M
+};
+
+struct __packed nct6694_i2c_cmd0 {
+	u8 port;
+	u8 br;
+	u8 addr;
+	u8 w_cnt;
+	u8 r_cnt;
+	u8 rsv[11];
+	u8 write_data[0x40];
+	u8 read_data[0x40];
+};
+
+struct nct6694_i2c_data {
+	struct nct6694 *nct6694;
+	struct i2c_adapter adapter;
+	unsigned char *xmit_buf;
+	unsigned char port;
+	unsigned char br;
+};
+
+static int nct6694_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
+{
+	struct nct6694_i2c_data *data = adap->algo_data;
+	struct nct6694_i2c_cmd0 *cmd = (struct nct6694_i2c_cmd0 *)data->xmit_buf;
+	int ret, i;
+
+	for (i = 0; i < num ; i++) {
+		struct i2c_msg *msg_temp = &msgs[i];
+
+		memset(data->xmit_buf, 0, sizeof(struct nct6694_i2c_cmd0));
+
+		if (msg_temp->len > 64)
+			return -EPROTO;
+		cmd->port = data->port;
+		cmd->br = data->br;
+		cmd->addr = i2c_8bit_addr_from_msg(msg_temp);
+		if (msg_temp->flags & I2C_M_RD) {
+			cmd->r_cnt = msg_temp->len;
+			ret = nct6694_write_msg(data->nct6694, NCT6694_I2C_MOD,
+						NCT6694_I2C_CMD0_OFFSET,
+						NCT6694_I2C_CMD0_LEN,
+						cmd);
+			if (ret < 0)
+				return 0;
+
+			memcpy(msg_temp->buf, cmd->read_data, msg_temp->len);
+		} else {
+			cmd->w_cnt = msg_temp->len;
+			memcpy(cmd->write_data, msg_temp->buf, msg_temp->len);
+			ret = nct6694_write_msg(data->nct6694, NCT6694_I2C_MOD,
+						NCT6694_I2C_CMD0_OFFSET,
+						NCT6694_I2C_CMD0_LEN,
+						cmd);
+			if (ret < 0)
+				return 0;
+		}
+	}
+
+	return num;
+}
+
+static u32 nct6694_func(struct i2c_adapter *adapter)
+{
+	return (I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL);
+}
+
+static const struct i2c_algorithm algorithm = {
+	.master_xfer = nct6694_xfer,
+	.functionality = nct6694_func,
+};
+
+static int nct6694_i2c_probe(struct platform_device *pdev)
+{
+	const struct mfd_cell *cell = mfd_get_cell(pdev);
+	struct nct6694 *nct6694 = dev_get_drvdata(pdev->dev.parent);
+	struct nct6694_i2c_data *data;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->xmit_buf = devm_kcalloc(&pdev->dev, NCT6694_MAX_PACKET_SZ,
+				      sizeof(unsigned char), GFP_KERNEL);
+	if (!data->xmit_buf)
+		return -ENOMEM;
+
+	data->nct6694 = nct6694;
+	data->port = cell->id;
+	data->br = I2C_BR_100K;
+
+	sprintf(data->adapter.name, "NCT6694 I2C Adapter %d", cell->id);
+	data->adapter.owner = THIS_MODULE;
+	data->adapter.algo = &algorithm;
+	data->adapter.dev.parent = &pdev->dev;
+	data->adapter.algo_data = data;
+
+	platform_set_drvdata(pdev, data);
+
+	return i2c_add_adapter(&data->adapter);
+}
+
+static void nct6694_i2c_remove(struct platform_device *pdev)
+{
+	struct nct6694_i2c_data *data = platform_get_drvdata(pdev);
+
+	i2c_del_adapter(&data->adapter);
+}
+
+static struct platform_driver nct6694_i2c_driver = {
+	.driver = {
+		.name	= "nct6694-i2c",
+	},
+	.probe		= nct6694_i2c_probe,
+	.remove		= nct6694_i2c_remove,
+};
+
+module_platform_driver(nct6694_i2c_driver);
+
+MODULE_DESCRIPTION("USB-I2C adapter driver for NCT6694");
+MODULE_AUTHOR("Ming Yu <tmyu0@nuvoton.com>");
+MODULE_LICENSE("GPL");
-- 
2.34.1