rtc: add real-time clock driver for NVIDIA Tegra

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

Signed-off-by: Andrew Chew <achew@nvidia.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Wan ZongShun <mcuos.com@gmail.com>
Acked-by: Jon Mayo <jmayo@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 499 insertions, 0 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 4941cade319..e1878877399 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -985,4 +985,14 @@ config RTC_DRV_LPC32XX
           This driver can also be buillt as a module. If so, the module
           will be called rtc-lpc32xx.
 
+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 5f6c3838dcf..ca91c3c42e9 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 00000000000..2fc31aac3f4
--- /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;