Date:	Mon, 18 Oct 2010 16:33:16 -0700
From:	achew@...dia.com
To:	jmayo@...dia.com, a.zummo@...ertech.it, olof@...om.net,
	greg@...ah.com, mcuos.com@...il.com, konkers@...gle.com
Cc:	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
	rtc-linux@...glegroups.com, Andrew Chew <achew@...dia.com>
Subject: [PATCH 1/1 V4] rtc: Add real-time clock driver for Tegra.

From: Andrew Chew <achew@...dia.com>

This is a platform driver that supports the built-in real-time clock on
Tegra SOCs.

Signed-off-by: Andrew Chew <achew@...dia.com>
Acked-by: Alessandro Zummo <a.zummo@...ertech.it>
Acked-by: Wan ZongShun <mcuos.com@...il.com>
---
Applied Alessandro Zummo's corrections.
Applied Wan ZongShun's corrections.
Jon Mayo addressed comments by Erik Gilling, to wit:
  Removed RTC_TEGRA_RETRIES.
  Renamed macros to match the prefix used in the rest of the code.
  Improved function comments to provide more detail.
  Implemented the TODO in tegra_rtc_wait_while_busy(), commented.
  Removed tegra_rtc_write_not_busy.
  Fixed several places where tegra_rtc_check_busy() was called before a call to
    tegra_rtc_wait_while_busy().
  Removed locks on some read-only accesses.
  Commented the lock in tegra_rtc_read_time() to explain why it was necessary.
  Fixed race in tegra_rtc_alarm_irq_enable()
  Protect tegra_rtc_irq_handler() with a busy check that uses udelay().
  Fixed a race with clearing of all interrupts.  Only clear the ones that
    activated the interrupt.
  Added request_mem_region() (and a corresponding release_mem_region()).
  Protected tegra_rtc_suspend() with a busy flag check.
In addition:
  Removed unnecessary status/interrupt code from tegra_rtc_resume().
  Fixed all races and bad behavior with waiting/sleeping between spinlocks.

 drivers/rtc/Kconfig     |   10 +
 drivers/rtc/Makefile    |    1 +
 drivers/rtc/rtc-tegra.c |  488 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 499 insertions(+), 0 deletions(-)
 create mode 100644 drivers/rtc/rtc-tegra.c

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 2432541..ca0da79 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -963,4 +963,14 @@ config RTC_DRV_JZ4740
 	  This driver can also be buillt as a module. If so, the module
 	  will be called rtc-jz4740.
 
+config RTC_DRV_TEGRA
+	tristate "NVIDIA Tegra Internal RTC driver"
+	depends on RTC_CLASS && ARCH_TEGRA
+	help
+	  If you say yes here you get support for the
+	  Tegra 200 series internal RTC module.
+
+	  This drive can also be built as a module. If so, the module
+	  will be called rtc-tegra.
+
 endif # RTC_CLASS
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 4ff4b88..a7f3617 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -91,6 +91,7 @@ obj-$(CONFIG_RTC_DRV_STARFIRE)	+= rtc-starfire.o
 obj-$(CONFIG_RTC_DRV_STK17TA8)	+= rtc-stk17ta8.o
 obj-$(CONFIG_RTC_DRV_STMP)	+= rtc-stmp3xxx.o
 obj-$(CONFIG_RTC_DRV_SUN4V)	+= rtc-sun4v.o
+obj-$(CONFIG_RTC_DRV_TEGRA)	+= rtc-tegra.o
 obj-$(CONFIG_RTC_DRV_TEST)	+= rtc-test.o
 obj-$(CONFIG_RTC_DRV_TWL4030)	+= rtc-twl.o
 obj-$(CONFIG_RTC_DRV_TX4939)	+= rtc-tx4939.o
diff --git a/drivers/rtc/rtc-tegra.c b/drivers/rtc/rtc-tegra.c
new file mode 100644
index 0000000..2fc31aa
--- /dev/null
+++ b/drivers/rtc/rtc-tegra.c
@@ -0,0 +1,488 @@
+/*
+ * An RTC driver for the NVIDIA Tegra 200 series internal RTC.
+ *
+ * Copyright (c) 2010, NVIDIA Corporation.
+ *
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/irq.h>
+#include <linux/io.h>
+#include <linux/delay.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+
+/* set to 1 = busy every eight 32kHz clocks during copy of sec+msec to AHB */
+#define TEGRA_RTC_REG_BUSY			0x004
+#define TEGRA_RTC_REG_SECONDS			0x008
+/* when msec is read, the seconds are buffered into shadow seconds. */
+#define TEGRA_RTC_REG_SHADOW_SECONDS		0x00c
+#define TEGRA_RTC_REG_MILLI_SECONDS		0x010
+#define TEGRA_RTC_REG_SECONDS_ALARM0		0x014
+#define TEGRA_RTC_REG_SECONDS_ALARM1		0x018
+#define TEGRA_RTC_REG_MILLI_SECONDS_ALARM0	0x01c
+#define TEGRA_RTC_REG_INTR_MASK			0x028
+/* write 1 bits to clear status bits */
+#define TEGRA_RTC_REG_INTR_STATUS		0x02c
+
+/* bits in INTR_MASK */
+#define TEGRA_RTC_INTR_MASK_MSEC_CDN_ALARM	(1<<4)
+#define TEGRA_RTC_INTR_MASK_SEC_CDN_ALARM	(1<<3)
+#define TEGRA_RTC_INTR_MASK_MSEC_ALARM		(1<<2)
+#define TEGRA_RTC_INTR_MASK_SEC_ALARM1		(1<<1)
+#define TEGRA_RTC_INTR_MASK_SEC_ALARM0		(1<<0)
+
+/* bits in INTR_STATUS */
+#define TEGRA_RTC_INTR_STATUS_MSEC_CDN_ALARM	(1<<4)
+#define TEGRA_RTC_INTR_STATUS_SEC_CDN_ALARM	(1<<3)
+#define TEGRA_RTC_INTR_STATUS_MSEC_ALARM	(1<<2)
+#define TEGRA_RTC_INTR_STATUS_SEC_ALARM1	(1<<1)
+#define TEGRA_RTC_INTR_STATUS_SEC_ALARM0	(1<<0)
+
+struct tegra_rtc_info {
+	struct platform_device	*pdev;
+	struct rtc_device	*rtc_dev;
+	void __iomem		*rtc_base; /* NULL if not initialized. */
+	int			tegra_rtc_irq; /* alarm and periodic irq */
+	spinlock_t		tegra_rtc_lock;
+};
+
+/* RTC hardware is busy when it is updating its values over AHB once
+ * every eight 32kHz clocks (~250uS).
+ * outside of these updates the CPU is free to write.
+ * CPU is always free to read.
+ */
+static inline u32 tegra_rtc_check_busy(struct tegra_rtc_info *info)
+{
+	return readl(info->rtc_base + TEGRA_RTC_REG_BUSY) & 1;
+}
+
+/* Wait for hardware to be ready for writing.
+ * This function tries to maximize the amount of time before the next update.
+ * It does this by waiting for the RTC to become busy with its periodic update,
+ * then returning once the RTC first becomes not busy.
+ * This periodic update (where the seconds and milliseconds are copied to the
+ * AHB side) occurs every eight 32kHz clocks (~250uS).
+ * The behavior of this function allows us to make some assumptions without
+ * introducing a race, because 250uS is plenty of time to read/write a value.
+ */
+static int tegra_rtc_wait_while_busy(struct device *dev)
+{
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+
+	int retries = 500; /* ~490 us is the worst case, ~250 us is best. */
+
+	/* first wait for the RTC to become busy. this is when it
+	 * posts its updated seconds+msec registers to AHB side. */
+	while (tegra_rtc_check_busy(info)) {
+		if (!retries--)
+			goto retry_failed;
+		udelay(1);
+	}
+
+	/* now we have about 250 us to manipulate registers */
+	return 0;
+
+retry_failed:
+	dev_err(dev, "write failed:retry count exceeded.\n");
+	return -ETIMEDOUT;
+}
+
+static int tegra_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+	unsigned long sec, msec;
+	unsigned long sl_irq_flags;
+
+	/* RTC hardware copies seconds to shadow seconds when a read
+	 * of milliseconds occurs. use a lock to keep other threads out. */
+	spin_lock_irqsave(&info->tegra_rtc_lock, sl_irq_flags);
+
+	msec = readl(info->rtc_base + TEGRA_RTC_REG_MILLI_SECONDS);
+	sec = readl(info->rtc_base + TEGRA_RTC_REG_SHADOW_SECONDS);
+
+	spin_unlock_irqrestore(&info->tegra_rtc_lock, sl_irq_flags);
+
+	rtc_time_to_tm(sec, tm);
+
+	dev_vdbg(dev, "time read as %lu. %d/%d/%d %d:%02u:%02u\n",
+		sec,
+		tm->tm_mon + 1,
+		tm->tm_mday,
+		tm->tm_year + 1900,
+		tm->tm_hour,
+		tm->tm_min,
+		tm->tm_sec
+	);
+
+	return 0;
+}
+
+static int tegra_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+	unsigned long sec;
+	int ret;
+
+	/* convert tm to seconds. */
+	ret = rtc_valid_tm(tm);
+	if (ret)
+		return ret;
+
+	rtc_tm_to_time(tm, &sec);
+
+	dev_vdbg(dev, "time set to %lu. %d/%d/%d %d:%02u:%02u\n",
+		sec,
+		tm->tm_mon+1,
+		tm->tm_mday,
+		tm->tm_year+1900,
+		tm->tm_hour,
+		tm->tm_min,
+		tm->tm_sec
+	);
+
+	/* seconds only written if wait succeeded. */
+	ret = tegra_rtc_wait_while_busy(dev);
+	if (!ret)
+		writel(sec, info->rtc_base + TEGRA_RTC_REG_SECONDS);
+
+	dev_vdbg(dev, "time read back as %d\n",
+		readl(info->rtc_base + TEGRA_RTC_REG_SECONDS));
+
+	return ret;
+}
+
+static int tegra_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+	unsigned long sec;
+	unsigned tmp;
+
+	sec = readl(info->rtc_base + TEGRA_RTC_REG_SECONDS_ALARM0);
+
+	if (sec == 0) {
+		/* alarm is disabled. */
+		alarm->enabled = 0;
+		alarm->time.tm_mon = -1;
+		alarm->time.tm_mday = -1;
+		alarm->time.tm_year = -1;
+		alarm->time.tm_hour = -1;
+		alarm->time.tm_min = -1;
+		alarm->time.tm_sec = -1;
+	} else {
+		/* alarm is enabled. */
+		alarm->enabled = 1;
+		rtc_time_to_tm(sec, &alarm->time);
+	}
+
+	tmp = readl(info->rtc_base + TEGRA_RTC_REG_INTR_STATUS);
+	alarm->pending = (tmp & TEGRA_RTC_INTR_STATUS_SEC_ALARM0) != 0;
+
+	return 0;
+}
+
+static int tegra_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+	unsigned status;
+	unsigned long sl_irq_flags;
+
+	tegra_rtc_wait_while_busy(dev);
+	spin_lock_irqsave(&info->tegra_rtc_lock, sl_irq_flags);
+
+	/* read the original value, and OR in the flag. */
+	status = readl(info->rtc_base + TEGRA_RTC_REG_INTR_MASK);
+	if (enabled)
+		status |= TEGRA_RTC_INTR_MASK_SEC_ALARM0; /* set it */
+	else
+		status &= ~TEGRA_RTC_INTR_MASK_SEC_ALARM0; /* clear it */
+
+	writel(status, info->rtc_base + TEGRA_RTC_REG_INTR_MASK);
+
+	spin_unlock_irqrestore(&info->tegra_rtc_lock, sl_irq_flags);
+
+	return 0;
+}
+
+static int tegra_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+	unsigned long sec;
+
+	if (alarm->enabled)
+		rtc_tm_to_time(&alarm->time, &sec);
+	else
+		sec = 0;
+
+	tegra_rtc_wait_while_busy(dev);
+	writel(sec, info->rtc_base + TEGRA_RTC_REG_SECONDS_ALARM0);
+	dev_vdbg(dev, "alarm read back as %d\n",
+		readl(info->rtc_base + TEGRA_RTC_REG_SECONDS_ALARM0));
+
+	/* if successfully written and alarm is enabled ... */
+	if (sec) {
+		tegra_rtc_alarm_irq_enable(dev, 1);
+
+		dev_vdbg(dev, "alarm set as %lu. %d/%d/%d %d:%02u:%02u\n",
+			sec,
+			alarm->time.tm_mon+1,
+			alarm->time.tm_mday,
+			alarm->time.tm_year+1900,
+			alarm->time.tm_hour,
+			alarm->time.tm_min,
+			alarm->time.tm_sec);
+	} else {
+		/* disable alarm if 0 or write error. */
+		dev_vdbg(dev, "alarm disabled\n");
+		tegra_rtc_alarm_irq_enable(dev, 0);
+	}
+
+	return 0;
+}
+
+static int tegra_rtc_proc(struct device *dev, struct seq_file *seq)
+{
+	if (!dev || !dev->driver)
+		return 0;
+
+	return seq_printf(seq, "name\t\t: %s\n", dev_name(dev));
+}
+
+static irqreturn_t tegra_rtc_irq_handler(int irq, void *data)
+{
+	struct device *dev = data;
+	struct tegra_rtc_info *info = dev_get_drvdata(dev);
+	unsigned long events = 0;
+	unsigned status;
+	unsigned long sl_irq_flags;
+
+	status = readl(info->rtc_base + TEGRA_RTC_REG_INTR_STATUS);
+	if (status) {
+		/* clear the interrupt masks and status on any irq. */
+		tegra_rtc_wait_while_busy(dev);
+		spin_lock_irqsave(&info->tegra_rtc_lock, sl_irq_flags);
+		writel(0, info->rtc_base + TEGRA_RTC_REG_INTR_MASK);
+		writel(status, info->rtc_base + TEGRA_RTC_REG_INTR_STATUS);
+		spin_unlock_irqrestore(&info->tegra_rtc_lock, sl_irq_flags);
+	}
+
+	/* check if Alarm */
+	if ((status & TEGRA_RTC_INTR_STATUS_SEC_ALARM0))
+		events |= RTC_IRQF | RTC_AF;
+
+	/* check if Periodic */
+	if ((status & TEGRA_RTC_INTR_STATUS_SEC_CDN_ALARM))
+		events |= RTC_IRQF | RTC_PF;
+
+	rtc_update_irq(info->rtc_dev, 1, events);
+
+	return IRQ_HANDLED;
+}
+
+static struct rtc_class_ops tegra_rtc_ops = {
+	.read_time	= tegra_rtc_read_time,
+	.set_time	= tegra_rtc_set_time,
+	.read_alarm	= tegra_rtc_read_alarm,
+	.set_alarm	= tegra_rtc_set_alarm,
+	.proc		= tegra_rtc_proc,
+	.alarm_irq_enable = tegra_rtc_alarm_irq_enable,
+};
+
+static int __devinit tegra_rtc_probe(struct platform_device *pdev)
+{
+	struct tegra_rtc_info *info;
+	struct resource *res;
+	int ret;
+
+	info = kzalloc(sizeof(struct tegra_rtc_info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res) {
+		dev_err(&pdev->dev,
+			"Unable to allocate resources for device.\n");
+		ret = -EBUSY;
+		goto err_free_info;
+	}
+
+	if (!request_mem_region(res->start, resource_size(res), pdev->name)) {
+		dev_err(&pdev->dev,
+			"Unable to request mem region for device.\n");
+		ret = -EBUSY;
+		goto err_free_info;
+	}
+
+	info->tegra_rtc_irq = platform_get_irq(pdev, 0);
+	if (info->tegra_rtc_irq <= 0) {
+		ret = -EBUSY;
+		goto err_release_mem_region;
+	}
+
+	info->rtc_base = ioremap_nocache(res->start, resource_size(res));
+	if (!info->rtc_base) {
+		dev_err(&pdev->dev, "Unable to grab IOs for device.\n");
+		ret = -EBUSY;
+		goto err_release_mem_region;
+	}
+
+	/* set context info. */
+	info->pdev = pdev;
+	info->tegra_rtc_lock = __SPIN_LOCK_UNLOCKED(info->tegra_rtc_lock);
+
+	platform_set_drvdata(pdev, info);
+
+	/* clear out the hardware. */
+	writel(0, info->rtc_base + TEGRA_RTC_REG_SECONDS_ALARM0);
+	writel(0xffffffff, info->rtc_base + TEGRA_RTC_REG_INTR_STATUS);
+	writel(0, info->rtc_base + TEGRA_RTC_REG_INTR_MASK);
+
+	device_init_wakeup(&pdev->dev, 1);
+
+	info->rtc_dev = rtc_device_register(
+		pdev->name, &pdev->dev, &tegra_rtc_ops, THIS_MODULE);
+	if (IS_ERR(info->rtc_dev)) {
+		ret = PTR_ERR(info->rtc_dev);
+		info->rtc_dev = NULL;
+		dev_err(&pdev->dev,
+			"Unable to register device (err=%d).\n",
+			ret);
+		goto err_iounmap;
+	}
+
+	ret = request_irq(info->tegra_rtc_irq, tegra_rtc_irq_handler,
+		IRQF_TRIGGER_HIGH, "rtc alarm", &pdev->dev);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"Unable to request interrupt for device (err=%d).\n",
+			ret);
+		goto err_dev_unreg;
+	}
+
+	dev_notice(&pdev->dev, "Tegra internal Real Time Clock\n");
+
+	return 0;
+
+err_dev_unreg:
+	rtc_device_unregister(info->rtc_dev);
+err_iounmap:
+	iounmap(info->rtc_base);
+err_release_mem_region:
+	release_mem_region(res->start, resource_size(res));
+err_free_info:
+	kfree(info);
+
+	return ret;
+}
+
+static int __devexit tegra_rtc_remove(struct platform_device *pdev)
+{
+	struct tegra_rtc_info *info = platform_get_drvdata(pdev);
+	struct resource *res;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -EBUSY;
+
+	free_irq(info->tegra_rtc_irq, &pdev->dev);
+	rtc_device_unregister(info->rtc_dev);
+	iounmap(info->rtc_base);
+	release_mem_region(res->start, resource_size(res));
+	kfree(info);
+
+	platform_set_drvdata(pdev, NULL);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM
+static int tegra_rtc_suspend(struct platform_device *pdev, pm_message_t state)
+{
+	struct device *dev = &pdev->dev;
+	struct tegra_rtc_info *info = platform_get_drvdata(pdev);
+
+	tegra_rtc_wait_while_busy(dev);
+
+	/* only use ALARM0 as a wake source. */
+	writel(0xffffffff, info->rtc_base + TEGRA_RTC_REG_INTR_STATUS);
+	writel(TEGRA_RTC_INTR_STATUS_SEC_ALARM0,
+		info->rtc_base + TEGRA_RTC_REG_INTR_MASK);
+
+	dev_vdbg(dev, "alarm sec = %d\n",
+		readl(info->rtc_base + TEGRA_RTC_REG_SECONDS_ALARM0));
+
+	dev_vdbg(dev, "Suspend (device_may_wakeup=%d) irq:%d\n",
+		device_may_wakeup(dev), info->tegra_rtc_irq);
+
+	/* leave the alarms on as a wake source. */
+	if (device_may_wakeup(dev))
+		enable_irq_wake(info->tegra_rtc_irq);
+
+	return 0;
+}
+
+static int tegra_rtc_resume(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct tegra_rtc_info *info = platform_get_drvdata(pdev);
+
+	dev_vdbg(dev, "Resume (device_may_wakeup=%d)\n",
+		device_may_wakeup(dev));
+	/* alarms were left on as a wake source, turn them off. */
+	if (device_may_wakeup(dev))
+		disable_irq_wake(info->tegra_rtc_irq);
+
+	return 0;
+}
+#endif
+
+static void tegra_rtc_shutdown(struct platform_device *pdev)
+{
+	dev_vdbg(&pdev->dev, "disabling interrupts.\n");
+	tegra_rtc_alarm_irq_enable(&pdev->dev, 0);
+}
+
+MODULE_ALIAS("platform:tegra_rtc");
+static struct platform_driver tegra_rtc_driver = {
+	.remove		= __devexit_p(tegra_rtc_remove),
+	.shutdown	= tegra_rtc_shutdown,
+	.driver		= {
+		.name	= "tegra_rtc",
+		.owner	= THIS_MODULE,
+	},
+#ifdef CONFIG_PM
+	.suspend	= tegra_rtc_suspend,
+	.resume		= tegra_rtc_resume,
+#endif
+};
+
+static int __init tegra_rtc_init(void)
+{
+	return platform_driver_probe(&tegra_rtc_driver, tegra_rtc_probe);
+}
+module_init(tegra_rtc_init);
+
+static void __exit tegra_rtc_exit(void)
+{
+	platform_driver_unregister(&tegra_rtc_driver);
+}
+module_exit(tegra_rtc_exit);
+
+MODULE_AUTHOR("Jon Mayo <jmayo@...dia.com>");
+MODULE_DESCRIPTION("driver for Tegra internal RTC");
+MODULE_LICENSE("GPL");
-- 
1.7.0.4

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