Blackfin: on-chip RTC controller driver

This patch implements the driver necessary use the Analog Devices Blackfin
processor's on-chip RTC controller.
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/Kconfig

@@ -354,4 +354,14 @@ 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_BFIN
+	tristate "Blackfin On-Chip RTC"
+	depends on RTC_CLASS && BFIN
+	help
+	  If you say yes here you will get support for the
+	  Blackfin On-Chip Real Time Clock.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-bfin.
+
 endmenu

drivers/rtc/Makefile

@@ -38,3 +38,4 @@ obj-$(CONFIG_RTC_DRV_MAX6902)	+= rtc-max6902.o
 obj-$(CONFIG_RTC_DRV_V3020)	+= rtc-v3020.o
 obj-$(CONFIG_RTC_DRV_AT91RM9200)+= rtc-at91rm9200.o
 obj-$(CONFIG_RTC_DRV_SH)	+= rtc-sh.o
+obj-$(CONFIG_RTC_DRV_BFIN)	+= rtc-bfin.o

drivers/rtc/rtc-bfin.c

+/*
+ * Blackfin On-Chip Real Time Clock Driver
+ *  Supports BF531/BF532/BF533/BF534/BF536/BF537
+ *
+ * Copyright 2004-2007 Analog Devices Inc.
+ *
+ * Enter bugs at http://blackfin.uclinux.org/
+ *
+ * Licensed under the GPL-2 or later.
+ */
+
+/* The biggest issue we deal with in this driver is that register writes are
+ * synced to the RTC frequency of 1Hz.  So if you write to a register and
+ * attempt to write again before the first write has completed, the new write
+ * is simply discarded.  This can easily be troublesome if userspace disables
+ * one event (say periodic) and then right after enables an event (say alarm).
+ * Since all events are maintained in the same interrupt mask register, if
+ * we wrote to it to disable the first event and then wrote to it again to
+ * enable the second event, that second event would not be enabled as the
+ * write would be discarded and things quickly fall apart.
+ *
+ * To keep this delay from significantly degrading performance (we, in theory,
+ * would have to sleep for up to 1 second everytime we wanted to write a
+ * register), we only check the write pending status before we start to issue
+ * a new write.  We bank on the idea that it doesnt matter when the sync
+ * happens so long as we don't attempt another write before it does.  The only
+ * time userspace would take this penalty is when they try and do multiple
+ * operations right after another ... but in this case, they need to take the
+ * sync penalty, so we should be OK.
+ *
+ * Also note that the RTC_ISTAT register does not suffer this penalty; its
+ * writes to clear status registers complete immediately.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/bcd.h>
+#include <linux/rtc.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/seq_file.h>
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/delay.h>
+
+#include <asm/blackfin.h>
+
+#define stamp(fmt, args...) pr_debug("%s:%i: " fmt "\n", __FUNCTION__, __LINE__, ## args)
+#define stampit() stamp("here i am")
+
+struct bfin_rtc {
+	struct rtc_device *rtc_dev;
+	struct rtc_time rtc_alarm;
+	spinlock_t lock;
+};
+
+/* Bit values for the ISTAT / ICTL registers */
+#define RTC_ISTAT_WRITE_COMPLETE  0x8000
+#define RTC_ISTAT_WRITE_PENDING   0x4000
+#define RTC_ISTAT_ALARM_DAY       0x0040
+#define RTC_ISTAT_24HR            0x0020
+#define RTC_ISTAT_HOUR            0x0010
+#define RTC_ISTAT_MIN             0x0008
+#define RTC_ISTAT_SEC             0x0004
+#define RTC_ISTAT_ALARM           0x0002
+#define RTC_ISTAT_STOPWATCH       0x0001
+
+/* Shift values for RTC_STAT register */
+#define DAY_BITS_OFF    17
+#define HOUR_BITS_OFF   12
+#define MIN_BITS_OFF    6
+#define SEC_BITS_OFF    0
+
+/* Some helper functions to convert between the common RTC notion of time
+ * and the internal Blackfin notion that is stored in 32bits.
+ */
+static inline u32 rtc_time_to_bfin(unsigned long now)
+{
+	u32 sec  = (now % 60);
+	u32 min  = (now % (60 * 60)) / 60;
+	u32 hour = (now % (60 * 60 * 24)) / (60 * 60);
+	u32 days = (now / (60 * 60 * 24));
+	return (sec  << SEC_BITS_OFF) +
+	       (min  << MIN_BITS_OFF) +
+	       (hour << HOUR_BITS_OFF) +
+	       (days << DAY_BITS_OFF);
+}
+static inline unsigned long rtc_bfin_to_time(u32 rtc_bfin)
+{
+	return (((rtc_bfin >> SEC_BITS_OFF)  & 0x003F)) +
+	       (((rtc_bfin >> MIN_BITS_OFF)  & 0x003F) * 60) +
+	       (((rtc_bfin >> HOUR_BITS_OFF) & 0x001F) * 60 * 60) +
+	       (((rtc_bfin >> DAY_BITS_OFF)  & 0x7FFF) * 60 * 60 * 24);
+}
+static inline void rtc_bfin_to_tm(u32 rtc_bfin, struct rtc_time *tm)
+{
+	rtc_time_to_tm(rtc_bfin_to_time(rtc_bfin), tm);
+}
+
+/* Wait for the previous write to a RTC register to complete.
+ * Unfortunately, we can't sleep here as that introduces a race condition when
+ * turning on interrupt events.  Consider this:
+ *  - process sets alarm
+ *  - process enables alarm
+ *  - process sleeps while waiting for rtc write to sync
+ *  - interrupt fires while process is sleeping
+ *  - interrupt acks the event by writing to ISTAT
+ *  - interrupt sets the WRITE PENDING bit
+ *  - interrupt handler finishes
+ *  - process wakes up, sees WRITE PENDING bit set, goes to sleep
+ *  - interrupt fires while process is sleeping
+ * If anyone can point out the obvious solution here, i'm listening :).  This
+ * shouldn't be an issue on an SMP or preempt system as this function should
+ * only be called with the rtc lock held.
+ */
+static void rtc_bfin_sync_pending(void)
+{
+	stampit();
+	while (!(bfin_read_RTC_ISTAT() & RTC_ISTAT_WRITE_COMPLETE)) {
+		if (!(bfin_read_RTC_ISTAT() & RTC_ISTAT_WRITE_PENDING))
+			break;
+	}
+	bfin_write_RTC_ISTAT(RTC_ISTAT_WRITE_COMPLETE);
+}
+
+static void rtc_bfin_reset(struct bfin_rtc *rtc)
+{
+	/* Initialize the RTC. Enable pre-scaler to scale RTC clock
+	 * to 1Hz and clear interrupt/status registers. */
+	spin_lock_irq(&rtc->lock);
+	rtc_bfin_sync_pending();
+	bfin_write_RTC_PREN(0x1);
+	bfin_write_RTC_ICTL(0);
+	bfin_write_RTC_SWCNT(0);
+	bfin_write_RTC_ALARM(0);
+	bfin_write_RTC_ISTAT(0xFFFF);
+	spin_unlock_irq(&rtc->lock);
+}
+
+static irqreturn_t bfin_rtc_interrupt(int irq, void *dev_id)
+{
+	struct platform_device *pdev = to_platform_device(dev_id);
+	struct bfin_rtc *rtc = platform_get_drvdata(pdev);
+	unsigned long events = 0;
+	u16 rtc_istat;
+
+	stampit();
+
+	spin_lock_irq(&rtc->lock);
+
+	rtc_istat = bfin_read_RTC_ISTAT();
+
+	if (rtc_istat & (RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY)) {
+		bfin_write_RTC_ISTAT(RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY);
+		events |= RTC_AF | RTC_IRQF;
+	}
+
+	if (rtc_istat & RTC_ISTAT_STOPWATCH) {
+		bfin_write_RTC_ISTAT(RTC_ISTAT_STOPWATCH);
+		events |= RTC_PF | RTC_IRQF;
+		bfin_write_RTC_SWCNT(rtc->rtc_dev->irq_freq);
+	}
+
+	if (rtc_istat & RTC_ISTAT_SEC) {
+		bfin_write_RTC_ISTAT(RTC_ISTAT_SEC);
+		events |= RTC_UF | RTC_IRQF;
+	}
+
+	rtc_update_irq(rtc->rtc_dev, 1, events);
+
+	spin_unlock_irq(&rtc->lock);
+
+	return IRQ_HANDLED;
+}
+
+static int bfin_rtc_open(struct device *dev)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+	int ret;
+
+	stampit();
+
+	ret = request_irq(IRQ_RTC, bfin_rtc_interrupt, IRQF_DISABLED, "rtc-bfin", dev);
+	if (unlikely(ret)) {
+		dev_err(dev, "request RTC IRQ failed with %d\n", ret);
+		return ret;
+	}
+
+	rtc_bfin_reset(rtc);
+
+	return ret;
+}
+
+static void bfin_rtc_release(struct device *dev)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+	stampit();
+	rtc_bfin_reset(rtc);
+	free_irq(IRQ_RTC, dev);
+}
+
+static int bfin_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+
+	stampit();
+
+	switch (cmd) {
+	case RTC_PIE_ON:
+		stampit();
+		spin_lock_irq(&rtc->lock);
+		rtc_bfin_sync_pending();
+		bfin_write_RTC_ISTAT(RTC_ISTAT_STOPWATCH);
+		bfin_write_RTC_SWCNT(rtc->rtc_dev->irq_freq);
+		bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() | RTC_ISTAT_STOPWATCH);
+		spin_unlock_irq(&rtc->lock);
+		return 0;
+	case RTC_PIE_OFF:
+		stampit();
+		spin_lock_irq(&rtc->lock);
+		rtc_bfin_sync_pending();
+		bfin_write_RTC_SWCNT(0);
+		bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() & ~RTC_ISTAT_STOPWATCH);
+		spin_unlock_irq(&rtc->lock);
+		return 0;
+
+	case RTC_UIE_ON:
+		stampit();
+		spin_lock_irq(&rtc->lock);
+		rtc_bfin_sync_pending();
+		bfin_write_RTC_ISTAT(RTC_ISTAT_SEC);
+		bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() | RTC_ISTAT_SEC);
+		spin_unlock_irq(&rtc->lock);
+		return 0;
+	case RTC_UIE_OFF:
+		stampit();
+		spin_lock_irq(&rtc->lock);
+		rtc_bfin_sync_pending();
+		bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() & ~RTC_ISTAT_SEC);
+		spin_unlock_irq(&rtc->lock);
+		return 0;
+
+	case RTC_AIE_ON: {
+		unsigned long rtc_alarm;
+		u16 which_alarm;
+		int ret = 0;
+
+		stampit();
+
+		spin_lock_irq(&rtc->lock);
+
+		rtc_bfin_sync_pending();
+		if (rtc->rtc_alarm.tm_yday == -1) {
+			struct rtc_time now;
+			rtc_bfin_to_tm(bfin_read_RTC_STAT(), &now);
+			now.tm_sec = rtc->rtc_alarm.tm_sec;
+			now.tm_min = rtc->rtc_alarm.tm_min;
+			now.tm_hour = rtc->rtc_alarm.tm_hour;
+			ret = rtc_tm_to_time(&now, &rtc_alarm);
+			which_alarm = RTC_ISTAT_ALARM;
+		} else {
+			ret = rtc_tm_to_time(&rtc->rtc_alarm, &rtc_alarm);
+			which_alarm = RTC_ISTAT_ALARM_DAY;
+		}
+		if (ret == 0) {
+			bfin_write_RTC_ISTAT(which_alarm);
+			bfin_write_RTC_ALARM(rtc_time_to_bfin(rtc_alarm));
+			bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() | which_alarm);
+		}
+
+		spin_unlock_irq(&rtc->lock);
+
+		return ret;
+	}
+	case RTC_AIE_OFF:
+		stampit();
+		spin_lock_irq(&rtc->lock);
+		rtc_bfin_sync_pending();
+		bfin_write_RTC_ICTL(bfin_read_RTC_ICTL() & ~(RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY));
+		spin_unlock_irq(&rtc->lock);
+		return 0;
+	}
+
+	return -ENOIOCTLCMD;
+}
+
+static int bfin_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+
+	stampit();
+
+	spin_lock_irq(&rtc->lock);
+	rtc_bfin_sync_pending();
+	rtc_bfin_to_tm(bfin_read_RTC_STAT(), tm);
+	spin_unlock_irq(&rtc->lock);
+
+	return 0;
+}
+
+static int bfin_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+	int ret;
+	unsigned long now;
+
+	stampit();
+
+	spin_lock_irq(&rtc->lock);
+
+	ret = rtc_tm_to_time(tm, &now);
+	if (ret == 0) {
+		rtc_bfin_sync_pending();
+		bfin_write_RTC_STAT(rtc_time_to_bfin(now));
+	}
+
+	spin_unlock_irq(&rtc->lock);
+
+	return ret;
+}
+
+static int bfin_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+	stampit();
+	memcpy(&alrm->time, &rtc->rtc_alarm, sizeof(struct rtc_time));
+	alrm->pending = !!(bfin_read_RTC_ICTL() & (RTC_ISTAT_ALARM | RTC_ISTAT_ALARM_DAY));
+	return 0;
+}
+
+static int bfin_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+	stampit();
+	memcpy(&rtc->rtc_alarm, &alrm->time, sizeof(struct rtc_time));
+	return 0;
+}
+
+static int bfin_rtc_proc(struct device *dev, struct seq_file *seq)
+{
+#define yesno(x) (x ? "yes" : "no")
+	u16 ictl = bfin_read_RTC_ICTL();
+	stampit();
+	seq_printf(seq, "alarm_IRQ\t: %s\n", yesno(ictl & RTC_ISTAT_ALARM));
+	seq_printf(seq, "wkalarm_IRQ\t: %s\n", yesno(ictl & RTC_ISTAT_ALARM_DAY));
+	seq_printf(seq, "seconds_IRQ\t: %s\n", yesno(ictl & RTC_ISTAT_SEC));
+	seq_printf(seq, "periodic_IRQ\t: %s\n", yesno(ictl & RTC_ISTAT_STOPWATCH));
+#ifdef DEBUG
+	seq_printf(seq, "RTC_STAT\t: 0x%08X\n", bfin_read_RTC_STAT());
+	seq_printf(seq, "RTC_ICTL\t: 0x%04X\n", bfin_read_RTC_ICTL());
+	seq_printf(seq, "RTC_ISTAT\t: 0x%04X\n", bfin_read_RTC_ISTAT());
+	seq_printf(seq, "RTC_SWCNT\t: 0x%04X\n", bfin_read_RTC_SWCNT());
+	seq_printf(seq, "RTC_ALARM\t: 0x%08X\n", bfin_read_RTC_ALARM());
+	seq_printf(seq, "RTC_PREN\t: 0x%04X\n", bfin_read_RTC_PREN());
+#endif
+	return 0;
+}
+
+static int bfin_irq_set_freq(struct device *dev, int freq)
+{
+	struct bfin_rtc *rtc = dev_get_drvdata(dev);
+	stampit();
+	rtc->rtc_dev->irq_freq = freq;
+	return 0;
+}
+
+static struct rtc_class_ops bfin_rtc_ops = {
+	.open          = bfin_rtc_open,
+	.release       = bfin_rtc_release,
+	.ioctl         = bfin_rtc_ioctl,
+	.read_time     = bfin_rtc_read_time,
+	.set_time      = bfin_rtc_set_time,
+	.read_alarm    = bfin_rtc_read_alarm,
+	.set_alarm     = bfin_rtc_set_alarm,
+	.proc          = bfin_rtc_proc,
+	.irq_set_freq  = bfin_irq_set_freq,
+};
+
+static int __devinit bfin_rtc_probe(struct platform_device *pdev)
+{
+	struct bfin_rtc *rtc;
+	int ret = 0;
+
+	stampit();
+
+	rtc = kzalloc(sizeof(*rtc), GFP_KERNEL);
+	if (unlikely(!rtc))
+		return -ENOMEM;
+
+	spin_lock_init(&rtc->lock);
+
+	rtc->rtc_dev = rtc_device_register(pdev->name, &pdev->dev, &bfin_rtc_ops, THIS_MODULE);
+	if (unlikely(IS_ERR(rtc))) {
+		ret = PTR_ERR(rtc->rtc_dev);
+		goto err;
+	}
+	rtc->rtc_dev->irq_freq = 0;
+	rtc->rtc_dev->max_user_freq = (2 << 16); /* stopwatch is an unsigned 16 bit reg */
+
+	platform_set_drvdata(pdev, rtc);
+
+	return 0;
+
+err:
+	kfree(rtc);
+	return ret;
+}
+
+static int __devexit bfin_rtc_remove(struct platform_device *pdev)
+{
+	struct bfin_rtc *rtc = platform_get_drvdata(pdev);
+
+	rtc_device_unregister(rtc->rtc_dev);
+	platform_set_drvdata(pdev, NULL);
+	kfree(rtc);
+
+	return 0;
+}
+
+static struct platform_driver bfin_rtc_driver = {
+	.driver		= {
+		.name	= "rtc-bfin",
+		.owner	= THIS_MODULE,
+	},
+	.probe		= bfin_rtc_probe,
+	.remove		= __devexit_p(bfin_rtc_remove),
+};
+
+static int __init bfin_rtc_init(void)
+{
+	stampit();
+	return platform_driver_register(&bfin_rtc_driver);
+}
+
+static void __exit bfin_rtc_exit(void)
+{
+	platform_driver_unregister(&bfin_rtc_driver);
+}
+
+module_init(bfin_rtc_init);
+module_exit(bfin_rtc_exit);
+
+MODULE_DESCRIPTION("Blackfin On-Chip Real Time Clock Driver");
+MODULE_AUTHOR("Mike Frysinger <vapier@gentoo.org>");
+MODULE_LICENSE("GPL");