rtc: add NXP PCF8523 support

Add an RTC driver for PCF8523 chips by NXP Semiconductors.  No support is
currently provided for the alarm and interrupt functions.  Only the time
and date functionality is implemented.
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/Kconfig

@@ -269,6 +269,15 @@ config RTC_DRV_X1205
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-x1205.
 
+config RTC_DRV_PCF8523
+	tristate "NXP PCF8523"
+	help
+	  If you say yes here you get support for the NXP PCF8523 RTC
+	  chips.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-pcf8523.
+
 config RTC_DRV_PCF8563
 	tristate "Philips PCF8563/Epson RTC8564"
 	help

drivers/rtc/Makefile

@@ -76,6 +76,7 @@ obj-$(CONFIG_RTC_DRV_MV)	+= rtc-mv.o
 obj-$(CONFIG_RTC_DRV_NUC900)	+= rtc-nuc900.o
 obj-$(CONFIG_RTC_DRV_OMAP)	+= rtc-omap.o
 obj-$(CONFIG_RTC_DRV_PCAP)	+= rtc-pcap.o
+obj-$(CONFIG_RTC_DRV_PCF8523)	+= rtc-pcf8523.o
 obj-$(CONFIG_RTC_DRV_PCF8563)	+= rtc-pcf8563.o
 obj-$(CONFIG_RTC_DRV_PCF8583)	+= rtc-pcf8583.o
 obj-$(CONFIG_RTC_DRV_PCF2123)	+= rtc-pcf2123.o

drivers/rtc/rtc-pcf8523.c

+/*
+ * Copyright (C) 2012 Avionic Design GmbH
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/bcd.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/of.h>
+
+#define DRIVER_NAME "rtc-pcf8523"
+
+#define REG_CONTROL1 0x00
+#define REG_CONTROL1_CAP_SEL (1 << 7)
+#define REG_CONTROL1_STOP    (1 << 5)
+
+#define REG_CONTROL3 0x02
+#define REG_CONTROL3_PM_BLD (1 << 7) /* battery low detection disabled */
+#define REG_CONTROL3_PM_VDD (1 << 6) /* switch-over disabled */
+#define REG_CONTROL3_PM_DSM (1 << 5) /* direct switching mode */
+#define REG_CONTROL3_PM_MASK 0xe0
+
+#define REG_SECONDS  0x03
+#define REG_SECONDS_OS (1 << 7)
+
+#define REG_MINUTES  0x04
+#define REG_HOURS    0x05
+#define REG_DAYS     0x06
+#define REG_WEEKDAYS 0x07
+#define REG_MONTHS   0x08
+#define REG_YEARS    0x09
+
+struct pcf8523 {
+	struct rtc_device *rtc;
+};
+
+static int pcf8523_read(struct i2c_client *client, u8 reg, u8 *valuep)
+{
+	struct i2c_msg msgs[2];
+	u8 value = 0;
+	int err;
+
+	msgs[0].addr = client->addr;
+	msgs[0].flags = 0;
+	msgs[0].len = sizeof(reg);
+	msgs[0].buf = &reg;
+
+	msgs[1].addr = client->addr;
+	msgs[1].flags = I2C_M_RD;
+	msgs[1].len = sizeof(value);
+	msgs[1].buf = &value;
+
+	err = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (err < 0)
+		return err;
+
+	*valuep = value;
+
+	return 0;
+}
+
+static int pcf8523_write(struct i2c_client *client, u8 reg, u8 value)
+{
+	u8 buffer[2] = { reg, value };
+	struct i2c_msg msg;
+	int err;
+
+	msg.addr = client->addr;
+	msg.flags = 0;
+	msg.len = sizeof(buffer);
+	msg.buf = buffer;
+
+	err = i2c_transfer(client->adapter, &msg, 1);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int pcf8523_select_capacitance(struct i2c_client *client, bool high)
+{
+	u8 value;
+	int err;
+
+	err = pcf8523_read(client, REG_CONTROL1, &value);
+	if (err < 0)
+		return err;
+
+	if (!high)
+		value &= ~REG_CONTROL1_CAP_SEL;
+	else
+		value |= REG_CONTROL1_CAP_SEL;
+
+	err = pcf8523_write(client, REG_CONTROL1, value);
+	if (err < 0)
+		return err;
+
+	return err;
+}
+
+static int pcf8523_set_pm(struct i2c_client *client, u8 pm)
+{
+	u8 value;
+	int err;
+
+	err = pcf8523_read(client, REG_CONTROL3, &value);
+	if (err < 0)
+		return err;
+
+	value = (value & ~REG_CONTROL3_PM_MASK) | pm;
+
+	err = pcf8523_write(client, REG_CONTROL3, value);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int pcf8523_stop_rtc(struct i2c_client *client)
+{
+	u8 value;
+	int err;
+
+	err = pcf8523_read(client, REG_CONTROL1, &value);
+	if (err < 0)
+		return err;
+
+	value |= REG_CONTROL1_STOP;
+
+	err = pcf8523_write(client, REG_CONTROL1, value);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int pcf8523_start_rtc(struct i2c_client *client)
+{
+	u8 value;
+	int err;
+
+	err = pcf8523_read(client, REG_CONTROL1, &value);
+	if (err < 0)
+		return err;
+
+	value &= ~REG_CONTROL1_STOP;
+
+	err = pcf8523_write(client, REG_CONTROL1, value);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int pcf8523_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	u8 start = REG_SECONDS, regs[7];
+	struct i2c_msg msgs[2];
+	int err;
+
+	msgs[0].addr = client->addr;
+	msgs[0].flags = 0;
+	msgs[0].len = 1;
+	msgs[0].buf = &start;
+
+	msgs[1].addr = client->addr;
+	msgs[1].flags = I2C_M_RD;
+	msgs[1].len = sizeof(regs);
+	msgs[1].buf = regs;
+
+	err = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (err < 0)
+		return err;
+
+	if (regs[0] & REG_SECONDS_OS) {
+		/*
+		 * If the oscillator was stopped, try to clear the flag. Upon
+		 * power-up the flag is always set, but if we cannot clear it
+		 * the oscillator isn't running properly for some reason. The
+		 * sensible thing therefore is to return an error, signalling
+		 * that the clock cannot be assumed to be correct.
+		 */
+
+		regs[0] &= ~REG_SECONDS_OS;
+
+		err = pcf8523_write(client, REG_SECONDS, regs[0]);
+		if (err < 0)
+			return err;
+
+		err = pcf8523_read(client, REG_SECONDS, &regs[0]);
+		if (err < 0)
+			return err;
+
+		if (regs[0] & REG_SECONDS_OS)
+			return -EAGAIN;
+	}
+
+	tm->tm_sec = bcd2bin(regs[0] & 0x7f);
+	tm->tm_min = bcd2bin(regs[1] & 0x7f);
+	tm->tm_hour = bcd2bin(regs[2] & 0x3f);
+	tm->tm_mday = bcd2bin(regs[3] & 0x3f);
+	tm->tm_wday = regs[4] & 0x7;
+	tm->tm_mon = bcd2bin(regs[5] & 0x1f);
+	tm->tm_year = bcd2bin(regs[6]) + 100;
+
+	return rtc_valid_tm(tm);
+}
+
+static int pcf8523_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct i2c_msg msg;
+	u8 regs[8];
+	int err;
+
+	err = pcf8523_stop_rtc(client);
+	if (err < 0)
+		return err;
+
+	regs[0] = REG_SECONDS;
+	regs[1] = bin2bcd(tm->tm_sec);
+	regs[2] = bin2bcd(tm->tm_min);
+	regs[3] = bin2bcd(tm->tm_hour);
+	regs[4] = bin2bcd(tm->tm_mday);
+	regs[5] = tm->tm_wday;
+	regs[6] = bin2bcd(tm->tm_mon);
+	regs[7] = bin2bcd(tm->tm_year - 100);
+
+	msg.addr = client->addr;
+	msg.flags = 0;
+	msg.len = sizeof(regs);
+	msg.buf = regs;
+
+	err = i2c_transfer(client->adapter, &msg, 1);
+	if (err < 0) {
+		/*
+		 * If the time cannot be set, restart the RTC anyway. Note
+		 * that errors are ignored if the RTC cannot be started so
+		 * that we have a chance to propagate the original error.
+		 */
+		pcf8523_start_rtc(client);
+		return err;
+	}
+
+	return pcf8523_start_rtc(client);
+}
+
+static const struct rtc_class_ops pcf8523_rtc_ops = {
+	.read_time = pcf8523_rtc_read_time,
+	.set_time = pcf8523_rtc_set_time,
+};
+
+static int pcf8523_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct pcf8523 *pcf;
+	int err;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	pcf = devm_kzalloc(&client->dev, sizeof(*pcf), GFP_KERNEL);
+	if (!pcf)
+		return -ENOMEM;
+
+	err = pcf8523_select_capacitance(client, true);
+	if (err < 0)
+		return err;
+
+	err = pcf8523_set_pm(client, 0);
+	if (err < 0)
+		return err;
+
+	pcf->rtc = rtc_device_register(DRIVER_NAME, &client->dev,
+				       &pcf8523_rtc_ops, THIS_MODULE);
+	if (IS_ERR(pcf->rtc))
+		return PTR_ERR(pcf->rtc);
+
+	i2c_set_clientdata(client, pcf);
+
+	return 0;
+}
+
+static int pcf8523_remove(struct i2c_client *client)
+{
+	struct pcf8523 *pcf = i2c_get_clientdata(client);
+
+	rtc_device_unregister(pcf->rtc);
+
+	return 0;
+}
+
+static const struct i2c_device_id pcf8523_id[] = {
+	{ "pcf8523", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, pcf8523_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id pcf8523_of_match[] = {
+	{ .compatible = "nxp,pcf8523" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, pcf8523_of_match);
+#endif
+
+static struct i2c_driver pcf8523_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+		.owner = THIS_MODULE,
+		.of_match_table = of_match_ptr(pcf8523_of_match),
+	},
+	.probe = pcf8523_probe,
+	.remove = pcf8523_remove,
+	.id_table = pcf8523_id,
+};
+module_i2c_driver(pcf8523_driver);
+
+MODULE_AUTHOR("Thierry Reding <thierry.reding@avionic-design.de>");
+MODULE_DESCRIPTION("NXP PCF8523 RTC driver");
+MODULE_LICENSE("GPL v2");