rtc: sd3078: new driver.

The sd3078 is a combination RTC and SRAM device with I2C interface.
Signed-off-by: Dianlong Li <long17.cool@163.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

MAINTAINERS

@@ -16458,6 +16458,12 @@ L:	linux-gpio@vger.kernel.org
 S:	Maintained
 F:	drivers/gpio/gpio-wcove.c
 
+WHWAVE RTC DRIVER
+M:	Dianlong Li <long17.cool@163.com>
+L:	linux-rtc@vger.kernel.org
+S:	Maintained
+F:	drivers/rtc/rtc-sd3078.c
+
 WIIMOTE HID DRIVER
 M:	David Herrmann <dh.herrmann@googlemail.com>
 L:	linux-input@vger.kernel.org

drivers/rtc/Kconfig

@@ -646,6 +646,15 @@ config RTC_DRV_S5M
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-s5m.
 
+config RTC_DRV_SD3078
+    tristate "ZXW Crystal SD3078"
+    help
+      If you say yes here you get support for the ZXW Crystal
+      SD3078 RTC chips.
+
+      This driver can also be built as a module. If so, the module
+      will be called rtc-sd3078
+
 endif # I2C
 
 comment "SPI RTC drivers"

drivers/rtc/Makefile

@@ -149,6 +149,7 @@ obj-$(CONFIG_RTC_DRV_S3C)	+= rtc-s3c.o
 obj-$(CONFIG_RTC_DRV_S5M)	+= rtc-s5m.o
 obj-$(CONFIG_RTC_DRV_SA1100)	+= rtc-sa1100.o
 obj-$(CONFIG_RTC_DRV_SC27XX)	+= rtc-sc27xx.o
+obj-$(CONFIG_RTC_DRV_SD3078)   += rtc-sd3078.o
 obj-$(CONFIG_RTC_DRV_SH)	+= rtc-sh.o
 obj-$(CONFIG_RTC_DRV_SIRFSOC)	+= rtc-sirfsoc.o
 obj-$(CONFIG_RTC_DRV_SNVS)	+= rtc-snvs.o

drivers/rtc/rtc-sd3078.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Real Time Clock (RTC) Driver for sd3078
+ * Copyright (C) 2018 Zoro Li
+ */
+
+#include <linux/bcd.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+#define SD3078_REG_SC			0x00
+#define SD3078_REG_MN			0x01
+#define SD3078_REG_HR			0x02
+#define SD3078_REG_DW			0x03
+#define SD3078_REG_DM			0x04
+#define SD3078_REG_MO			0x05
+#define SD3078_REG_YR			0x06
+
+#define SD3078_REG_CTRL1		0x0f
+#define SD3078_REG_CTRL2		0x10
+#define SD3078_REG_CTRL3		0x11
+
+#define KEY_WRITE1		0x80
+#define KEY_WRITE2		0x04
+#define KEY_WRITE3		0x80
+
+#define NUM_TIME_REGS   (SD3078_REG_YR - SD3078_REG_SC + 1)
+
+/*
+ * The sd3078 has write protection
+ * and we can choose whether or not to use it.
+ * Write protection is turned off by default.
+ */
+#define WRITE_PROTECT_EN	0
+
+struct sd3078 {
+	struct rtc_device	*rtc;
+	struct regmap		*regmap;
+};
+
+/*
+ * In order to prevent arbitrary modification of the time register,
+ * when modification of the register,
+ * the "write" bit needs to be written in a certain order.
+ * 1. set WRITE1 bit
+ * 2. set WRITE2 bit
+ * 3. set WRITE3 bit
+ */
+static void sd3078_enable_reg_write(struct sd3078 *sd3078)
+{
+	regmap_update_bits(sd3078->regmap, SD3078_REG_CTRL2,
+			   KEY_WRITE1, KEY_WRITE1);
+	regmap_update_bits(sd3078->regmap, SD3078_REG_CTRL1,
+			   KEY_WRITE2, KEY_WRITE2);
+	regmap_update_bits(sd3078->regmap, SD3078_REG_CTRL1,
+			   KEY_WRITE3, KEY_WRITE3);
+}
+
+#if WRITE_PROTECT_EN
+/*
+ * In order to prevent arbitrary modification of the time register,
+ * we should disable the write function.
+ * when disable write,
+ * the "write" bit needs to be clear in a certain order.
+ * 1. clear WRITE2 bit
+ * 2. clear WRITE3 bit
+ * 3. clear WRITE1 bit
+ */
+static void sd3078_disable_reg_write(struct sd3078 *sd3078)
+{
+	regmap_update_bits(sd3078->regmap, SD3078_REG_CTRL1,
+			   KEY_WRITE2, 0);
+	regmap_update_bits(sd3078->regmap, SD3078_REG_CTRL1,
+			   KEY_WRITE3, 0);
+	regmap_update_bits(sd3078->regmap, SD3078_REG_CTRL2,
+			   KEY_WRITE1, 0);
+}
+#endif
+
+static int sd3078_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned char hour;
+	unsigned char rtc_data[NUM_TIME_REGS] = {0};
+	struct i2c_client *client = to_i2c_client(dev);
+	struct sd3078 *sd3078 = i2c_get_clientdata(client);
+	int ret;
+
+	ret = regmap_bulk_read(sd3078->regmap, SD3078_REG_SC, rtc_data,
+			       NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "reading from RTC failed with err:%d\n", ret);
+		return ret;
+	}
+
+	tm->tm_sec	= bcd2bin(rtc_data[SD3078_REG_SC] & 0x7F);
+	tm->tm_min	= bcd2bin(rtc_data[SD3078_REG_MN] & 0x7F);
+
+	/*
+	 * The sd3078 supports 12/24 hour mode.
+	 * When getting time,
+	 * we need to convert the 12 hour mode to the 24 hour mode.
+	 */
+	hour = rtc_data[SD3078_REG_HR];
+	if (hour & 0x80) /* 24H MODE */
+		tm->tm_hour = bcd2bin(rtc_data[SD3078_REG_HR] & 0x3F);
+	else if (hour & 0x20) /* 12H MODE PM */
+		tm->tm_hour = bcd2bin(rtc_data[SD3078_REG_HR] & 0x1F) + 12;
+	else /* 12H MODE AM */
+		tm->tm_hour = bcd2bin(rtc_data[SD3078_REG_HR] & 0x1F);
+
+	tm->tm_mday = bcd2bin(rtc_data[SD3078_REG_DM] & 0x3F);
+	tm->tm_wday = rtc_data[SD3078_REG_DW] & 0x07;
+	tm->tm_mon	= bcd2bin(rtc_data[SD3078_REG_MO] & 0x1F) - 1;
+	tm->tm_year = bcd2bin(rtc_data[SD3078_REG_YR]) + 100;
+
+	return 0;
+}
+
+static int sd3078_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned char rtc_data[NUM_TIME_REGS];
+	struct i2c_client *client = to_i2c_client(dev);
+	struct sd3078 *sd3078 = i2c_get_clientdata(client);
+	int ret;
+
+	rtc_data[SD3078_REG_SC] = bin2bcd(tm->tm_sec);
+	rtc_data[SD3078_REG_MN] = bin2bcd(tm->tm_min);
+	rtc_data[SD3078_REG_HR] = bin2bcd(tm->tm_hour) | 0x80;
+	rtc_data[SD3078_REG_DM] = bin2bcd(tm->tm_mday);
+	rtc_data[SD3078_REG_DW] = tm->tm_wday & 0x07;
+	rtc_data[SD3078_REG_MO] = bin2bcd(tm->tm_mon) + 1;
+	rtc_data[SD3078_REG_YR] = bin2bcd(tm->tm_year - 100);
+
+#if WRITE_PROTECT_EN
+	sd3078_enable_reg_write(sd3078);
+#endif
+
+	ret = regmap_bulk_write(sd3078->regmap, SD3078_REG_SC, rtc_data,
+				NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "writing to RTC failed with err:%d\n", ret);
+		return ret;
+	}
+
+#if WRITE_PROTECT_EN
+	sd3078_disable_reg_write(sd3078);
+#endif
+
+	return 0;
+}
+
+static const struct rtc_class_ops sd3078_rtc_ops = {
+	.read_time	= sd3078_rtc_read_time,
+	.set_time	= sd3078_rtc_set_time,
+};
+
+static const struct regmap_config regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = 0x11,
+};
+
+static int sd3078_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	int ret;
+	struct sd3078 *sd3078;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	sd3078 = devm_kzalloc(&client->dev, sizeof(*sd3078), GFP_KERNEL);
+	if (!sd3078)
+		return -ENOMEM;
+
+	sd3078->regmap = devm_regmap_init_i2c(client, &regmap_config);
+	if (IS_ERR(sd3078->regmap)) {
+		dev_err(&client->dev, "regmap allocation failed\n");
+		return PTR_ERR(sd3078->regmap);
+	}
+
+	i2c_set_clientdata(client, sd3078);
+
+	sd3078->rtc = devm_rtc_allocate_device(&client->dev);
+	if (IS_ERR(sd3078->rtc))
+		return PTR_ERR(sd3078->rtc);
+
+	sd3078->rtc->ops = &sd3078_rtc_ops;
+	sd3078->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	sd3078->rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	ret = rtc_register_device(sd3078->rtc);
+	if (ret) {
+		dev_err(&client->dev, "failed to register rtc device\n");
+		return ret;
+	}
+
+	sd3078_enable_reg_write(sd3078);
+
+	return 0;
+}
+
+static const struct i2c_device_id sd3078_id[] = {
+	{"sd3078", 0},
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, sd3078_id);
+
+static const struct of_device_id rtc_dt_match[] = {
+	{ .compatible = "whwave,sd3078" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, rtc_dt_match);
+
+struct i2c_driver sd3078_driver = {
+	.driver     = {
+		.name   = "sd3078",
+		.owner  = THIS_MODULE,
+		.of_match_table = of_match_ptr(rtc_dt_match),
+	},
+	.probe      = sd3078_probe,
+	.id_table   = sd3078_id,
+};
+
+module_i2c_driver(sd3078_driver);
+
+MODULE_AUTHOR("Dianlong Li <long17.cool@163.com>");
+MODULE_DESCRIPTION("SD3078 RTC driver");
+MODULE_LICENSE("GPL v2");