rtc: Add support for RTCs on Wolfson WM831x devices

The WM831x series of PMICs contain RTC functionality. The hardware
provides a 32 bit counter incrementing at 1Hz together with a per
tick interrupt and an alarm value. For simplicity the driver chooses
to define the epoch for the counter as the Unix epoch - if required
platform data can be used in future to customise this.

When powered on from a completely cold state the RTC reports that it
has not been configured - when this happens an error is returned
when attempting to read the RTC in order to avoid use of values we
know to be invalid.

The hardware also provides security features which mean that it can
ignore attempts to set the RTC time in certain circumstances, most
notably if the RTC is written to too often. These errors are detected
by verifying the written RTC value.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/rtc/Kconfig

@@ -518,6 +518,16 @@ config RTC_DRV_V3020
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-v3020.
 
+config RTC_DRV_WM831X
+	tristate "Wolfson Microelectronics WM831x RTC"
+	depends on MFD_WM831X
+	help
+	  If you say yes here you will get support for the RTC subsystem
+	  of the Wolfson Microelectronics WM831X series PMICs.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called "rtc-wm831x".
+
 config RTC_DRV_WM8350
 	tristate "Wolfson Microelectronics WM8350 RTC"
 	depends on MFD_WM8350

drivers/rtc/Makefile

@@ -74,6 +74,7 @@ obj-$(CONFIG_RTC_DRV_TWL4030)	+= rtc-twl4030.o
 obj-$(CONFIG_RTC_DRV_TX4939)	+= rtc-tx4939.o
 obj-$(CONFIG_RTC_DRV_V3020)	+= rtc-v3020.o
 obj-$(CONFIG_RTC_DRV_VR41XX)	+= rtc-vr41xx.o
+obj-$(CONFIG_RTC_DRV_WM831X)	+= rtc-wm831x.o
 obj-$(CONFIG_RTC_DRV_WM8350)	+= rtc-wm8350.o
 obj-$(CONFIG_RTC_DRV_X1205)	+= rtc-x1205.o
 obj-$(CONFIG_RTC_DRV_PCF50633)	+= rtc-pcf50633.o

drivers/rtc/rtc-wm831x.c

@@ -0,0 +1,523 @@
+/*
+ *	Real Time Clock driver for Wolfson Microelectronics WM831x
+ *
+ *	Copyright (C) 2009 Wolfson Microelectronics PLC.
+ *
+ *  Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
+ *
+ *  This program is free software; you can redistribute  it and/or modify it
+ *  under  the terms of  the GNU General  Public License as published by the
+ *  Free Software Foundation;  either version 2 of the  License, or (at your
+ *  option) any later version.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/time.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/interrupt.h>
+#include <linux/ioctl.h>
+#include <linux/completion.h>
+#include <linux/mfd/wm831x/core.h>
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+
+
+/*
+ * R16416 (0x4020) - RTC Write Counter
+ */
+#define WM831X_RTC_WR_CNT_MASK                  0xFFFF  /* RTC_WR_CNT - [15:0] */
+#define WM831X_RTC_WR_CNT_SHIFT                      0  /* RTC_WR_CNT - [15:0] */
+#define WM831X_RTC_WR_CNT_WIDTH                     16  /* RTC_WR_CNT - [15:0] */
+
+/*
+ * R16417 (0x4021) - RTC Time 1
+ */
+#define WM831X_RTC_TIME_MASK                    0xFFFF  /* RTC_TIME - [15:0] */
+#define WM831X_RTC_TIME_SHIFT                        0  /* RTC_TIME - [15:0] */
+#define WM831X_RTC_TIME_WIDTH                       16  /* RTC_TIME - [15:0] */
+
+/*
+ * R16418 (0x4022) - RTC Time 2
+ */
+#define WM831X_RTC_TIME_MASK                    0xFFFF  /* RTC_TIME - [15:0] */
+#define WM831X_RTC_TIME_SHIFT                        0  /* RTC_TIME - [15:0] */
+#define WM831X_RTC_TIME_WIDTH                       16  /* RTC_TIME - [15:0] */
+
+/*
+ * R16419 (0x4023) - RTC Alarm 1
+ */
+#define WM831X_RTC_ALM_MASK                     0xFFFF  /* RTC_ALM - [15:0] */
+#define WM831X_RTC_ALM_SHIFT                         0  /* RTC_ALM - [15:0] */
+#define WM831X_RTC_ALM_WIDTH                        16  /* RTC_ALM - [15:0] */
+
+/*
+ * R16420 (0x4024) - RTC Alarm 2
+ */
+#define WM831X_RTC_ALM_MASK                     0xFFFF  /* RTC_ALM - [15:0] */
+#define WM831X_RTC_ALM_SHIFT                         0  /* RTC_ALM - [15:0] */
+#define WM831X_RTC_ALM_WIDTH                        16  /* RTC_ALM - [15:0] */
+
+/*
+ * R16421 (0x4025) - RTC Control
+ */
+#define WM831X_RTC_VALID                        0x8000  /* RTC_VALID */
+#define WM831X_RTC_VALID_MASK                   0x8000  /* RTC_VALID */
+#define WM831X_RTC_VALID_SHIFT                      15  /* RTC_VALID */
+#define WM831X_RTC_VALID_WIDTH                       1  /* RTC_VALID */
+#define WM831X_RTC_SYNC_BUSY                    0x4000  /* RTC_SYNC_BUSY */
+#define WM831X_RTC_SYNC_BUSY_MASK               0x4000  /* RTC_SYNC_BUSY */
+#define WM831X_RTC_SYNC_BUSY_SHIFT                  14  /* RTC_SYNC_BUSY */
+#define WM831X_RTC_SYNC_BUSY_WIDTH                   1  /* RTC_SYNC_BUSY */
+#define WM831X_RTC_ALM_ENA                      0x0400  /* RTC_ALM_ENA */
+#define WM831X_RTC_ALM_ENA_MASK                 0x0400  /* RTC_ALM_ENA */
+#define WM831X_RTC_ALM_ENA_SHIFT                    10  /* RTC_ALM_ENA */
+#define WM831X_RTC_ALM_ENA_WIDTH                     1  /* RTC_ALM_ENA */
+#define WM831X_RTC_PINT_FREQ_MASK               0x0070  /* RTC_PINT_FREQ - [6:4] */
+#define WM831X_RTC_PINT_FREQ_SHIFT                   4  /* RTC_PINT_FREQ - [6:4] */
+#define WM831X_RTC_PINT_FREQ_WIDTH                   3  /* RTC_PINT_FREQ - [6:4] */
+
+/*
+ * R16422 (0x4026) - RTC Trim
+ */
+#define WM831X_RTC_TRIM_MASK                    0x03FF  /* RTC_TRIM - [9:0] */
+#define WM831X_RTC_TRIM_SHIFT                        0  /* RTC_TRIM - [9:0] */
+#define WM831X_RTC_TRIM_WIDTH                       10  /* RTC_TRIM - [9:0] */
+
+#define WM831X_SET_TIME_RETRIES	5
+#define WM831X_GET_TIME_RETRIES	5
+
+struct wm831x_rtc {
+	struct wm831x *wm831x;
+	struct rtc_device *rtc;
+	unsigned int alarm_enabled:1;
+};
+
+/*
+ * Read current time and date in RTC
+ */
+static int wm831x_rtc_readtime(struct device *dev, struct rtc_time *tm)
+{
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(dev);
+	struct wm831x *wm831x = wm831x_rtc->wm831x;
+	u16 time1[2], time2[2];
+	int ret;
+	int count = 0;
+
+	/* Has the RTC been programmed? */
+	ret = wm831x_reg_read(wm831x, WM831X_RTC_CONTROL);
+	if (ret < 0) {
+		dev_err(dev, "Failed to read RTC control: %d\n", ret);
+		return ret;
+	}
+	if (!(ret & WM831X_RTC_VALID)) {
+		dev_dbg(dev, "RTC not yet configured\n");
+		return -EINVAL;
+	}
+
+	/* Read twice to make sure we don't read a corrupt, partially
+	 * incremented, value.
+	 */
+	do {
+		ret = wm831x_bulk_read(wm831x, WM831X_RTC_TIME_1,
+				       2, time1);
+		if (ret != 0)
+			continue;
+
+		ret = wm831x_bulk_read(wm831x, WM831X_RTC_TIME_1,
+				       2, time2);
+		if (ret != 0)
+			continue;
+
+		if (memcmp(time1, time2, sizeof(time1)) == 0) {
+			u32 time = (time1[0] << 16) | time1[1];
+
+			rtc_time_to_tm(time, tm);
+			return rtc_valid_tm(tm);
+		}
+
+	} while (++count < WM831X_GET_TIME_RETRIES);
+
+	dev_err(dev, "Timed out reading current time\n");
+
+	return -EIO;
+}
+
+/*
+ * Set current time and date in RTC
+ */
+static int wm831x_rtc_set_mmss(struct device *dev, unsigned long time)
+{
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(dev);
+	struct wm831x *wm831x = wm831x_rtc->wm831x;
+	struct rtc_time new_tm;
+	unsigned long new_time;
+	int ret;
+	int count = 0;
+
+	ret = wm831x_reg_write(wm831x, WM831X_RTC_TIME_1,
+			       (time >> 16) & 0xffff);
+	if (ret < 0) {
+		dev_err(dev, "Failed to write TIME_1: %d\n", ret);
+		return ret;
+	}
+
+	ret = wm831x_reg_write(wm831x, WM831X_RTC_TIME_2, time & 0xffff);
+	if (ret < 0) {
+		dev_err(dev, "Failed to write TIME_2: %d\n", ret);
+		return ret;
+	}
+
+	/* Wait for the update to complete - should happen first time
+	 * round but be conservative.
+	 */
+	do {
+		msleep(1);
+
+		ret = wm831x_reg_read(wm831x, WM831X_RTC_CONTROL);
+		if (ret < 0)
+			ret = WM831X_RTC_SYNC_BUSY;
+	} while (!(ret & WM831X_RTC_SYNC_BUSY) &&
+		 ++count < WM831X_SET_TIME_RETRIES);
+
+	if (ret & WM831X_RTC_SYNC_BUSY) {
+		dev_err(dev, "Timed out writing RTC update\n");
+		return -EIO;
+	}
+
+	/* Check that the update was accepted; security features may
+	 * have caused the update to be ignored.
+	 */
+	ret = wm831x_rtc_readtime(dev, &new_tm);
+	if (ret < 0)
+		return ret;
+
+	ret = rtc_tm_to_time(&new_tm, &new_time);
+	if (ret < 0) {
+		dev_err(dev, "Failed to convert time: %d\n", ret);
+		return ret;
+	}
+
+	/* Allow a second of change in case of tick */
+	if (new_time - time > 1) {
+		dev_err(dev, "RTC update not permitted by hardware\n");
+		return -EPERM;
+	}
+
+	return 0;
+}
+
+/*
+ * Read alarm time and date in RTC
+ */
+static int wm831x_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(dev);
+	int ret;
+	u16 data[2];
+	u32 time;
+
+	ret = wm831x_bulk_read(wm831x_rtc->wm831x, WM831X_RTC_ALARM_1,
+			       2, data);
+	if (ret != 0) {
+		dev_err(dev, "Failed to read alarm time: %d\n", ret);
+		return ret;
+	}
+
+	time = (data[0] << 16) | data[1];
+
+	rtc_time_to_tm(time, &alrm->time);
+
+	ret = wm831x_reg_read(wm831x_rtc->wm831x, WM831X_RTC_CONTROL);
+	if (ret < 0) {
+		dev_err(dev, "Failed to read RTC control: %d\n", ret);
+		return ret;
+	}
+
+	if (ret & WM831X_RTC_ALM_ENA)
+		alrm->enabled = 1;
+	else
+		alrm->enabled = 0;
+
+	return 0;
+}
+
+static int wm831x_rtc_stop_alarm(struct wm831x_rtc *wm831x_rtc)
+{
+	wm831x_rtc->alarm_enabled = 0;
+
+	return wm831x_set_bits(wm831x_rtc->wm831x, WM831X_RTC_CONTROL,
+			       WM831X_RTC_ALM_ENA, 0);
+}
+
+static int wm831x_rtc_start_alarm(struct wm831x_rtc *wm831x_rtc)
+{
+	wm831x_rtc->alarm_enabled = 1;
+
+	return wm831x_set_bits(wm831x_rtc->wm831x, WM831X_RTC_CONTROL,
+			       WM831X_RTC_ALM_ENA, WM831X_RTC_ALM_ENA);
+}
+
+static int wm831x_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(dev);
+	struct wm831x *wm831x = wm831x_rtc->wm831x;
+	int ret;
+	unsigned long time;
+
+	ret = rtc_tm_to_time(&alrm->time, &time);
+	if (ret < 0) {
+		dev_err(dev, "Failed to convert time: %d\n", ret);
+		return ret;
+	}
+
+	ret = wm831x_rtc_stop_alarm(wm831x_rtc);
+	if (ret < 0) {
+		dev_err(dev, "Failed to stop alarm: %d\n", ret);
+		return ret;
+	}
+
+	ret = wm831x_reg_write(wm831x, WM831X_RTC_ALARM_1,
+			       (time >> 16) & 0xffff);
+	if (ret < 0) {
+		dev_err(dev, "Failed to write ALARM_1: %d\n", ret);
+		return ret;
+	}
+
+	ret = wm831x_reg_write(wm831x, WM831X_RTC_ALARM_2, time & 0xffff);
+	if (ret < 0) {
+		dev_err(dev, "Failed to write ALARM_2: %d\n", ret);
+		return ret;
+	}
+
+	if (alrm->enabled) {
+		ret = wm831x_rtc_start_alarm(wm831x_rtc);
+		if (ret < 0) {
+			dev_err(dev, "Failed to start alarm: %d\n", ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int wm831x_rtc_alarm_irq_enable(struct device *dev,
+				       unsigned int enabled)
+{
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(dev);
+
+	if (enabled)
+		return wm831x_rtc_start_alarm(wm831x_rtc);
+	else
+		return wm831x_rtc_stop_alarm(wm831x_rtc);
+}
+
+static int wm831x_rtc_update_irq_enable(struct device *dev,
+					unsigned int enabled)
+{
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(dev);
+	int val;
+
+	if (enabled)
+		val = 1 << WM831X_RTC_PINT_FREQ_SHIFT;
+	else
+		val = 0;
+
+	return wm831x_set_bits(wm831x_rtc->wm831x, WM831X_RTC_CONTROL,
+			       WM831X_RTC_PINT_FREQ_MASK, val);
+}
+
+static irqreturn_t wm831x_alm_irq(int irq, void *data)
+{
+	struct wm831x_rtc *wm831x_rtc = data;
+
+	rtc_update_irq(wm831x_rtc->rtc, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t wm831x_per_irq(int irq, void *data)
+{
+	struct wm831x_rtc *wm831x_rtc = data;
+
+	rtc_update_irq(wm831x_rtc->rtc, 1, RTC_IRQF | RTC_UF);
+
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops wm831x_rtc_ops = {
+	.read_time = wm831x_rtc_readtime,
+	.set_mmss = wm831x_rtc_set_mmss,
+	.read_alarm = wm831x_rtc_readalarm,
+	.set_alarm = wm831x_rtc_setalarm,
+	.alarm_irq_enable = wm831x_rtc_alarm_irq_enable,
+	.update_irq_enable = wm831x_rtc_update_irq_enable,
+};
+
+#ifdef CONFIG_PM
+/* Turn off the alarm if it should not be a wake source. */
+static int wm831x_rtc_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(&pdev->dev);
+	int ret, enable;
+
+	if (wm831x_rtc->alarm_enabled && device_may_wakeup(&pdev->dev))
+		enable = WM831X_RTC_ALM_ENA;
+	else
+		enable = 0;
+
+	ret = wm831x_set_bits(wm831x_rtc->wm831x, WM831X_RTC_CONTROL,
+			      WM831X_RTC_ALM_ENA, enable);
+	if (ret != 0)
+		dev_err(&pdev->dev, "Failed to update RTC alarm: %d\n", ret);
+
+	return 0;
+}
+
+/* Enable the alarm if it should be enabled (in case it was disabled to
+ * prevent use as a wake source).
+ */
+static int wm831x_rtc_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(&pdev->dev);
+	int ret;
+
+	if (wm831x_rtc->alarm_enabled) {
+		ret = wm831x_rtc_start_alarm(wm831x_rtc);
+		if (ret != 0)
+			dev_err(&pdev->dev,
+				"Failed to restart RTC alarm: %d\n", ret);
+	}
+
+	return 0;
+}
+
+/* Unconditionally disable the alarm */
+static int wm831x_rtc_freeze(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct wm831x_rtc *wm831x_rtc = dev_get_drvdata(&pdev->dev);
+	int ret;
+
+	ret = wm831x_set_bits(wm831x_rtc->wm831x, WM831X_RTC_CONTROL,
+			      WM831X_RTC_ALM_ENA, 0);
+	if (ret != 0)
+		dev_err(&pdev->dev, "Failed to stop RTC alarm: %d\n", ret);
+
+	return 0;
+}
+#else
+#define wm831x_rtc_suspend NULL
+#define wm831x_rtc_resume NULL
+#define wm831x_rtc_freeze NULL
+#endif
+
+static int wm831x_rtc_probe(struct platform_device *pdev)
+{
+	struct wm831x *wm831x = dev_get_drvdata(pdev->dev.parent);
+	struct wm831x_rtc *wm831x_rtc;
+	int per_irq = platform_get_irq_byname(pdev, "PER");
+	int alm_irq = platform_get_irq_byname(pdev, "ALM");
+	int ret = 0;
+
+	wm831x_rtc = kzalloc(sizeof(*wm831x_rtc), GFP_KERNEL);
+	if (wm831x_rtc == NULL)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, wm831x_rtc);
+	wm831x_rtc->wm831x = wm831x;
+
+	ret = wm831x_reg_read(wm831x, WM831X_RTC_CONTROL);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to read RTC control: %d\n", ret);
+		goto err;
+	}
+	if (ret & WM831X_RTC_ALM_ENA)
+		wm831x_rtc->alarm_enabled = 1;
+
+	device_init_wakeup(&pdev->dev, 1);
+
+	wm831x_rtc->rtc = rtc_device_register("wm831x", &pdev->dev,
+					      &wm831x_rtc_ops, THIS_MODULE);
+	if (IS_ERR(wm831x_rtc->rtc)) {
+		ret = PTR_ERR(wm831x_rtc->rtc);
+		goto err;
+	}
+
+	ret = wm831x_request_irq(wm831x, per_irq, wm831x_per_irq,
+				 IRQF_TRIGGER_RISING, "wm831x_rtc_per",
+				 wm831x_rtc);
+	if (ret != 0) {
+		dev_err(&pdev->dev, "Failed to request periodic IRQ %d: %d\n",
+			per_irq, ret);
+	}
+
+	ret = wm831x_request_irq(wm831x, alm_irq, wm831x_alm_irq,
+				 IRQF_TRIGGER_RISING, "wm831x_rtc_alm",
+				 wm831x_rtc);
+	if (ret != 0) {
+		dev_err(&pdev->dev, "Failed to request alarm IRQ %d: %d\n",
+			alm_irq, ret);
+	}
+
+	return 0;
+
+err:
+	kfree(wm831x_rtc);
+	return ret;
+}
+
+static int __devexit wm831x_rtc_remove(struct platform_device *pdev)
+{
+	struct wm831x_rtc *wm831x_rtc = platform_get_drvdata(pdev);
+	int per_irq = platform_get_irq_byname(pdev, "PER");
+	int alm_irq = platform_get_irq_byname(pdev, "ALM");
+
+	wm831x_free_irq(wm831x_rtc->wm831x, alm_irq, wm831x_rtc);
+	wm831x_free_irq(wm831x_rtc->wm831x, per_irq, wm831x_rtc);
+	rtc_device_unregister(wm831x_rtc->rtc);
+	kfree(wm831x_rtc);
+
+	return 0;
+}
+
+static struct dev_pm_ops wm831x_rtc_pm_ops = {
+	.suspend = wm831x_rtc_suspend,
+	.resume = wm831x_rtc_resume,
+
+	.freeze = wm831x_rtc_freeze,
+	.thaw = wm831x_rtc_resume,
+	.restore = wm831x_rtc_resume,
+
+	.poweroff = wm831x_rtc_suspend,
+};
+
+static struct platform_driver wm831x_rtc_driver = {
+	.probe = wm831x_rtc_probe,
+	.remove = __devexit_p(wm831x_rtc_remove),
+	.driver = {
+		.name = "wm831x-rtc",
+		.pm = &wm831x_rtc_pm_ops,
+	},
+};
+
+static int __init wm831x_rtc_init(void)
+{
+	return platform_driver_register(&wm831x_rtc_driver);
+}
+module_init(wm831x_rtc_init);
+
+static void __exit wm831x_rtc_exit(void)
+{
+	platform_driver_unregister(&wm831x_rtc_driver);
+}
+module_exit(wm831x_rtc_exit);
+
+MODULE_AUTHOR("Mark Brown <broonie@opensource.wolfsonmicro.com>");
+MODULE_DESCRIPTION("RTC driver for the WM831x series PMICs");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:wm831x-rtc");