This driver supports RTC functionality for NCT6694 MFD device
based on USB interface.

Signed-off-by: Ming Yu <tmyu0@nuvoton.com>
---
 MAINTAINERS               |   1 +
 drivers/rtc/Kconfig       |  10 ++
 drivers/rtc/Makefile      |   1 +
 drivers/rtc/rtc-nct6694.c | 263 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 275 insertions(+)
 create mode 100644 drivers/rtc/rtc-nct6694.c

diff --git a/MAINTAINERS b/MAINTAINERS
index d6414eea0463..6d1cfec28076 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16550,6 +16550,7 @@ F:	drivers/hwmon/nct6694-hwmon.c
 F:	drivers/i2c/busses/i2c-nct6694.c
 F:	drivers/mfd/nct6694.c
 F:	drivers/net/can/nct6694_canfd.c
+F:	drivers/rtc/rtc-nct6694.c
 F:	drivers/watchdog/nct6694_wdt.c
 F:	include/linux/mfd/nct6694.h
 
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 66eb1122248b..36829d096194 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -406,6 +406,16 @@ config RTC_DRV_NCT3018Y
 	   This driver can also be built as a module, if so, the module will be
 	   called "rtc-nct3018y".
 
+config RTC_DRV_NCT6694
+	tristate "Nuvoton NCT6694 RTC support"
+	depends on MFD_NCT6694
+	help
+	  If you say yes to this option, support will be included for Nuvoton
+	  NCT6694, a USB device to RTC.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called rtc-nct6694.
+
 config RTC_DRV_RK808
 	tristate "Rockchip RK805/RK808/RK809/RK817/RK818 RTC"
 	depends on MFD_RK8XX
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index f62340ecc534..64443d26bb5b 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -116,6 +116,7 @@ obj-$(CONFIG_RTC_DRV_MXC)	+= rtc-mxc.o
 obj-$(CONFIG_RTC_DRV_MXC_V2)	+= rtc-mxc_v2.o
 obj-$(CONFIG_RTC_DRV_GAMECUBE)	+= rtc-gamecube.o
 obj-$(CONFIG_RTC_DRV_NCT3018Y)	+= rtc-nct3018y.o
+obj-$(CONFIG_RTC_DRV_NCT6694)	+= rtc-nct6694.o
 obj-$(CONFIG_RTC_DRV_NTXEC)	+= rtc-ntxec.o
 obj-$(CONFIG_RTC_DRV_OMAP)	+= rtc-omap.o
 obj-$(CONFIG_RTC_DRV_OPAL)	+= rtc-opal.o
diff --git a/drivers/rtc/rtc-nct6694.c b/drivers/rtc/rtc-nct6694.c
new file mode 100644
index 000000000000..097555a16b4f
--- /dev/null
+++ b/drivers/rtc/rtc-nct6694.c
@@ -0,0 +1,263 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Nuvoton NCT6694 RTC driver based on USB interface.
+ *
+ * Copyright (C) 2024 Nuvoton Technology Corp.
+ */
+
+#include <linux/bcd.h>
+#include <linux/irqdomain.h>
+#include <linux/kernel.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/nct6694.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+/* Host interface */
+#define NCT6694_RTC_MOD		0x08
+
+/* Message Channel */
+/* Command 00h */
+#define NCT6694_RTC_CMD0_LEN	0x07
+#define NCT6694_RTC_CMD0_OFFSET	0x0000	/* OFFSET = SEL|CMD */
+/* Command 01h */
+#define NCT6694_RTC_CMD1_LEN	0x05
+#define NCT6694_RTC_CMD1_OFFSET	0x0001	/* OFFSET = SEL|CMD */
+/* Command 02h */
+#define NCT6694_RTC_CMD2_LEN	0x02
+#define NCT6694_RTC_CMD2_OFFSET	0x0002	/* OFFSET = SEL|CMD */
+
+#define NCT6694_RTC_IRQ_INT_EN		BIT(0)	/* Transmit a USB INT-in when RTC alarm */
+#define NCT6694_RTC_IRQ_GPO_EN		BIT(5)	/* Trigger a GPO Low Pulse when RTC alarm */
+
+#define NCT6694_RTC_IRQ_EN		(NCT6694_RTC_IRQ_INT_EN | NCT6694_RTC_IRQ_GPO_EN)
+#define NCT6694_RTC_IRQ_STS		BIT(0)	/* Write 1 clear IRQ status */
+
+struct __packed nct6694_rtc_cmd0 {
+	u8 sec;
+	u8 min;
+	u8 hour;
+	u8 week;
+	u8 day;
+	u8 month;
+	u8 year;
+};
+
+struct __packed nct6694_rtc_cmd1 {
+	u8 sec;
+	u8 min;
+	u8 hour;
+	u8 alarm_en;
+	u8 alarm_pend;
+};
+
+struct __packed nct6694_rtc_cmd2 {
+	u8 irq_en;
+	u8 irq_pend;
+};
+
+struct nct6694_rtc_data {
+	struct nct6694 *nct6694;
+	struct rtc_device *rtc;
+	struct mutex lock;
+	unsigned char *xmit_buf;
+};
+
+static int nct6694_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct nct6694_rtc_data *data = dev_get_drvdata(dev);
+	struct nct6694_rtc_cmd0 *buf = (struct nct6694_rtc_cmd0 *)data->xmit_buf;
+	int ret;
+
+	guard(mutex)(&data->lock);
+
+	ret = nct6694_read_msg(data->nct6694, NCT6694_RTC_MOD,
+			       NCT6694_RTC_CMD0_OFFSET,
+			       NCT6694_RTC_CMD0_LEN,
+			       buf);
+	if (ret)
+		return ret;
+
+	tm->tm_sec = bcd2bin(buf->sec);		/* tm_sec expect 0 ~ 59 */
+	tm->tm_min = bcd2bin(buf->min);		/* tm_min expect 0 ~ 59 */
+	tm->tm_hour = bcd2bin(buf->hour);	/* tm_hour expect 0 ~ 23 */
+	tm->tm_wday = bcd2bin(buf->week) - 1;	/* tm_wday expect 0 ~ 6 */
+	tm->tm_mday = bcd2bin(buf->day);	/* tm_mday expect 1 ~ 31 */
+	tm->tm_mon = bcd2bin(buf->month) - 1;	/* tm_month expect 0 ~ 11 */
+	tm->tm_year = bcd2bin(buf->year) + 100;	/* tm_year expect since 1900 */
+
+	return ret;
+}
+
+static int nct6694_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct nct6694_rtc_data *data = dev_get_drvdata(dev);
+	struct nct6694_rtc_cmd0 *buf = (struct nct6694_rtc_cmd0 *)data->xmit_buf;
+
+	guard(mutex)(&data->lock);
+
+	buf->sec = bin2bcd(tm->tm_sec);
+	buf->min = bin2bcd(tm->tm_min);
+	buf->hour = bin2bcd(tm->tm_hour);
+	buf->week = bin2bcd(tm->tm_wday + 1);
+	buf->day = bin2bcd(tm->tm_mday);
+	buf->month = bin2bcd(tm->tm_mon + 1);
+	buf->year = bin2bcd(tm->tm_year - 100);
+
+	return nct6694_write_msg(data->nct6694, NCT6694_RTC_MOD,
+				 NCT6694_RTC_CMD0_OFFSET,
+				 NCT6694_RTC_CMD0_LEN,
+				 buf);
+}
+
+static int nct6694_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct nct6694_rtc_data *data = dev_get_drvdata(dev);
+	struct nct6694_rtc_cmd1 *buf = (struct nct6694_rtc_cmd1 *)data->xmit_buf;
+	int ret;
+
+	guard(mutex)(&data->lock);
+
+	ret = nct6694_read_msg(data->nct6694, NCT6694_RTC_MOD,
+			       NCT6694_RTC_CMD1_OFFSET,
+			       NCT6694_RTC_CMD1_LEN,
+			       buf);
+	if (ret)
+		return ret;
+
+	alrm->time.tm_sec = bcd2bin(buf->sec);
+	alrm->time.tm_min = bcd2bin(buf->min);
+	alrm->time.tm_hour = bcd2bin(buf->hour);
+	alrm->enabled = buf->alarm_en;
+	alrm->pending = buf->alarm_pend;
+
+	return ret;
+}
+
+static int nct6694_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct nct6694_rtc_data *data = dev_get_drvdata(dev);
+	struct nct6694_rtc_cmd1 *buf = (struct nct6694_rtc_cmd1 *)data->xmit_buf;
+
+	guard(mutex)(&data->lock);
+
+	buf->sec = bin2bcd(alrm->time.tm_sec);
+	buf->min = bin2bcd(alrm->time.tm_min);
+	buf->hour = bin2bcd(alrm->time.tm_hour);
+	buf->alarm_en = alrm->enabled ? NCT6694_RTC_IRQ_EN : 0;
+	buf->alarm_pend = 0;
+
+	return nct6694_write_msg(data->nct6694, NCT6694_RTC_MOD,
+				 NCT6694_RTC_CMD1_OFFSET,
+				 NCT6694_RTC_CMD1_LEN,
+				 buf);
+}
+
+static int nct6694_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct nct6694_rtc_data *data = dev_get_drvdata(dev);
+	struct nct6694_rtc_cmd2 *buf = (struct nct6694_rtc_cmd2 *)data->xmit_buf;
+
+	guard(mutex)(&data->lock);
+
+	if (enabled)
+		buf->irq_en |= NCT6694_RTC_IRQ_EN;
+	else
+		buf->irq_en &= ~NCT6694_RTC_IRQ_EN;
+
+	buf->irq_pend = 0;
+
+	return nct6694_write_msg(data->nct6694, NCT6694_RTC_MOD,
+				 NCT6694_RTC_CMD2_OFFSET,
+				 NCT6694_RTC_CMD2_LEN,
+				 buf);
+}
+
+static const struct rtc_class_ops nct6694_rtc_ops = {
+	.read_time = nct6694_rtc_read_time,
+	.set_time = nct6694_rtc_set_time,
+	.read_alarm = nct6694_rtc_read_alarm,
+	.set_alarm = nct6694_rtc_set_alarm,
+	.alarm_irq_enable = nct6694_rtc_alarm_irq_enable,
+};
+
+static irqreturn_t nct6694_irq(int irq, void *dev_id)
+{
+	struct nct6694_rtc_data *data = dev_id;
+	struct nct6694_rtc_cmd2 *buf = (struct nct6694_rtc_cmd2 *)data->xmit_buf;
+	int ret;
+
+	guard(mutex)(&data->lock);
+
+	buf->irq_en = NCT6694_RTC_IRQ_EN;
+	buf->irq_pend = NCT6694_RTC_IRQ_STS;
+	ret = nct6694_write_msg(data->nct6694, NCT6694_RTC_MOD,
+				NCT6694_RTC_CMD2_OFFSET,
+				NCT6694_RTC_CMD2_LEN,
+				buf);
+	if (ret)
+		return IRQ_NONE;
+
+	rtc_update_irq(data->rtc, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static int nct6694_rtc_probe(struct platform_device *pdev)
+{
+	struct nct6694_rtc_data *data;
+	struct nct6694 *nct6694 = dev_get_drvdata(pdev->dev.parent);
+	int ret, irq;
+
+	irq = irq_create_mapping(nct6694->domain, NCT6694_IRQ_RTC);
+	if (!irq)
+		return -EINVAL;
+
+	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->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(data->rtc))
+		return PTR_ERR(data->rtc);
+
+	data->nct6694 = nct6694;
+	data->rtc->ops = &nct6694_rtc_ops;
+	data->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	data->rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	mutex_init(&data->lock);
+
+	device_set_wakeup_capable(&pdev->dev, 1);
+
+	platform_set_drvdata(pdev, data);
+
+	ret = devm_request_threaded_irq(&pdev->dev, irq, NULL,
+					nct6694_irq, IRQF_ONESHOT,
+					"nct6694-rtc", data);
+	if (ret < 0)
+		return dev_err_probe(&pdev->dev, ret, "Failed to request irq\n");
+
+	/* Register rtc device to RTC framework */
+	return devm_rtc_register_device(data->rtc);
+}
+
+static struct platform_driver nct6694_rtc_driver = {
+	.driver = {
+		.name	= "nct6694-rtc",
+	},
+	.probe		= nct6694_rtc_probe,
+};
+
+module_platform_driver(nct6694_rtc_driver);
+
+MODULE_DESCRIPTION("USB-RTC driver for NCT6694");
+MODULE_AUTHOR("Ming Yu <tmyu0@nuvoton.com>");
+MODULE_LICENSE("GPL");
-- 
2.34.1