[PATCH v3 5/7] rtc: New driver for RTC in Netronix embedded controller

["Jonathan Neuschäfer" <j.neuschaefer@gmx.net>]

With this driver, mainline Linux can keep its time and date in sync with
the vendor kernel.

Advanced functionality like alarm and automatic power-on is not yet
supported.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
---

v3:
- Add email address to copyright line
- Remove OF compatible string and don't include linux/of_device.h
- Don't use a comma after sentinels
- Avoid ret |= ... pattern
- Move 8-bit register conversion to ntxec.h
- Relicense as GPLv2 or later

v2:
- https://lore.kernel.org/lkml/20200905133230.1014581-7-j.neuschaefer@gmx.net/
- Rework top-of-file comment [Lee Jones]
- Sort the #include lines [Alexandre Belloni]
- don't align = signs in struct initializers [Uwe Kleine-König]
- Switch to regmap
- Fix register number used to read minutes and seconds
- Prefix registers with NTXEC_REG_
- Add help text to the Kconfig option
- Use devm_rtc_allocate_device and rtc_register_device, set ->range_min and ->range_max
---
 drivers/rtc/Kconfig     |   8 +++
 drivers/rtc/Makefile    |   1 +
 drivers/rtc/rtc-ntxec.c | 132 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 141 insertions(+)
 create mode 100644 drivers/rtc/rtc-ntxec.c

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 48c536acd777f..ae8f3dc36c9a3 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -1301,6 +1301,14 @@ config RTC_DRV_CROS_EC
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-cros-ec.

+config RTC_DRV_NTXEC
+	tristate "Netronix embedded controller RTC driver"
+	depends on MFD_NTXEC
+	help
+	  Say yes here if you want to support the RTC functionality of the
+	  embedded controller found in certain e-book readers designed by the
+	  ODM Netronix.
+
 comment "on-CPU RTC drivers"

 config RTC_DRV_ASM9260
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 880e08a409c3d..733479db18896 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -111,6 +111,7 @@ obj-$(CONFIG_RTC_DRV_MT7622)	+= rtc-mt7622.o
 obj-$(CONFIG_RTC_DRV_MV)	+= rtc-mv.o
 obj-$(CONFIG_RTC_DRV_MXC)	+= rtc-mxc.o
 obj-$(CONFIG_RTC_DRV_MXC_V2)	+= rtc-mxc_v2.o
+obj-$(CONFIG_RTC_DRV_NTXEC)	+= rtc-ntxec.o
 obj-$(CONFIG_RTC_DRV_OMAP)	+= rtc-omap.o
 obj-$(CONFIG_RTC_DRV_OPAL)	+= rtc-opal.o
 obj-$(CONFIG_RTC_DRV_PALMAS)	+= rtc-palmas.o
diff --git a/drivers/rtc/rtc-ntxec.c b/drivers/rtc/rtc-ntxec.c
new file mode 100644
index 0000000000000..af23c7cc76544
--- /dev/null
+++ b/drivers/rtc/rtc-ntxec.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the ODM Netronix, Inc. It contains RTC,
+ * battery monitoring, system power management, and PWM functionality.
+ *
+ * This driver implements access to the RTC time and date.
+ *
+ * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>
+ */
+
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+#include <linux/types.h>
+
+struct ntxec_rtc {
+	struct device *dev;
+	struct ntxec *ec;
+};
+
+#define NTXEC_REG_WRITE_YEAR	0x10
+#define NTXEC_REG_WRITE_MONTH	0x11
+#define NTXEC_REG_WRITE_DAY	0x12
+#define NTXEC_REG_WRITE_HOUR	0x13
+#define NTXEC_REG_WRITE_MINUTE	0x14
+#define NTXEC_REG_WRITE_SECOND	0x15
+
+#define NTXEC_REG_READ_YM	0x20
+#define NTXEC_REG_READ_DH	0x21
+#define NTXEC_REG_READ_MS	0x23
+
+static int ntxec_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ntxec_rtc *rtc = dev_get_drvdata(dev);
+	unsigned int value;
+	int res;
+
+	res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_YM, &value);
+	if (res < 0)
+		return res;
+
+	tm->tm_year = (value >> 8) + 100;
+	tm->tm_mon = (value & 0xff) - 1;
+
+	res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_DH, &value);
+	if (res < 0)
+		return res;
+
+	tm->tm_mday = value >> 8;
+	tm->tm_hour = value & 0xff;
+
+	res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MS, &value);
+	if (res < 0)
+		return res;
+
+	tm->tm_min = value >> 8;
+	tm->tm_sec = value & 0xff;
+
+	return 0;
+}
+
+static int ntxec_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ntxec_rtc *rtc = dev_get_drvdata(dev);
+	int res = 0;
+
+	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_YEAR, ntxec_reg8(tm->tm_year - 100));
+	if (res)
+		return res;
+
+	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_MONTH, ntxec_reg8(tm->tm_mon + 1));
+	if (res)
+		return res;
+
+	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_DAY, ntxec_reg8(tm->tm_mday));
+	if (res)
+		return res;
+
+	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_HOUR, ntxec_reg8(tm->tm_hour));
+	if (res)
+		return res;
+
+	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_MINUTE, ntxec_reg8(tm->tm_min));
+	if (res)
+		return res;
+
+	return regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_SECOND, ntxec_reg8(tm->tm_sec));
+}
+
+static const struct rtc_class_ops ntxec_rtc_ops = {
+	.read_time = ntxec_read_time,
+	.set_time = ntxec_set_time,
+};
+
+static int ntxec_rtc_probe(struct platform_device *pdev)
+{
+	struct rtc_device *dev;
+	struct ntxec_rtc *rtc;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->dev = &pdev->dev;
+	rtc->ec = dev_get_drvdata(pdev->dev.parent);
+	platform_set_drvdata(pdev, rtc);
+
+	dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+
+	dev->ops = &ntxec_rtc_ops;
+	dev->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	dev->range_max = 9025257599LL; /* 2255-12-31 23:59:59 */
+
+	return rtc_register_device(dev);
+}
+
+static struct platform_driver ntxec_rtc_driver = {
+	.driver = {
+		.name = "ntxec-rtc",
+	},
+	.probe = ntxec_rtc_probe,
+};
+module_platform_driver(ntxec_rtc_driver);
+
+MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");
+MODULE_DESCRIPTION("RTC driver for Netronix EC");
+MODULE_LICENSE("GPL");
--
2.28.0