4 files changed, 150 insertions, 4 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index cdd97192dc69..4941cade319f 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -97,6 +97,18 @@ config RTC_INTF_DEV
 
           If unsure, say Y.
 
+config RTC_INTF_DEV_UIE_EMUL
+        bool "RTC UIE emulation on dev interface"
+        depends on RTC_INTF_DEV
+        help
+          Provides an emulation for RTC_UIE if the underlying rtc chip
+          driver does not expose RTC_UIE ioctls. Those requests generate
+          once-per-second update interrupts, used for synchronization.
+
+          The emulation code will read the time from the hardware
+          clock several times per second, please enable this option
+          only if you know that you really need it.
+
 config RTC_DRV_TEST
         tristate "Test driver/device"
         help
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index a0c01967244d..cb2f0728fd70 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -209,9 +209,8 @@ int rtc_alarm_irq_enable(struct rtc_device *rtc, unsigned int enabled)
         }
 
         if (err)
-                return err;
-
-        if (!rtc->ops)
+                /* nothing */;
+        else if (!rtc->ops)
                 err = -ENODEV;
         else if (!rtc->ops->alarm_irq_enable)
                 err = -EINVAL;
@@ -229,6 +228,12 @@ int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
         if (err)
                 return err;
 
+#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
+        if (enabled == 0 && rtc->uie_irq_active) {
+                mutex_unlock(&rtc->ops_lock);
+                return rtc_dev_update_irq_enable_emul(rtc, 0);
+        }
+#endif
         /* make sure we're changing state */
         if (rtc->uie_rtctimer.enabled == enabled)
                 goto out;
@@ -248,6 +253,16 @@ int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 
 out:
         mutex_unlock(&rtc->ops_lock);
+#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
+        /*
+         * Enable emulation if the driver did not provide
+         * the update_irq_enable function pointer or if returned
+         * -EINVAL to signal that it has been configured without
+         * interrupts or that are not available at the moment.
+         */
+        if (err == -EINVAL)
+                err = rtc_dev_update_irq_enable_emul(rtc, enabled);
+#endif
         return err;
 
 }
@@ -263,7 +278,7 @@ EXPORT_SYMBOL_GPL(rtc_update_irq_enable);
  *
  * Triggers the registered irq_task function callback.
  */
-static void rtc_handle_legacy_irq(struct rtc_device *rtc, int num, int mode)
+void rtc_handle_legacy_irq(struct rtc_device *rtc, int num, int mode)
 {
         unsigned long flags;
 
diff --git a/drivers/rtc/rtc-dev.c b/drivers/rtc/rtc-dev.c
index 37c3cc1b3dd5..d0e06edb14c5 100644
--- a/drivers/rtc/rtc-dev.c
+++ b/drivers/rtc/rtc-dev.c
@@ -46,6 +46,105 @@ static int rtc_dev_open(struct inode *inode, struct file *file)
         return err;
 }
 
+#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
+/*
+ * Routine to poll RTC seconds field for change as often as possible,
+ * after first RTC_UIE use timer to reduce polling
+ */
+static void rtc_uie_task(struct work_struct *work)
+{
+        struct rtc_device *rtc =
+                container_of(work, struct rtc_device, uie_task);
+        struct rtc_time tm;
+        int num = 0;
+        int err;
+
+        err = rtc_read_time(rtc, &tm);
+
+        spin_lock_irq(&rtc->irq_lock);
+        if (rtc->stop_uie_polling || err) {
+                rtc->uie_task_active = 0;
+        } else if (rtc->oldsecs != tm.tm_sec) {
+                num = (tm.tm_sec + 60 - rtc->oldsecs) % 60;
+                rtc->oldsecs = tm.tm_sec;
+                rtc->uie_timer.expires = jiffies + HZ - (HZ/10);
+                rtc->uie_timer_active = 1;
+                rtc->uie_task_active = 0;
+                add_timer(&rtc->uie_timer);
+        } else if (schedule_work(&rtc->uie_task) == 0) {
+                rtc->uie_task_active = 0;
+        }
+        spin_unlock_irq(&rtc->irq_lock);
+        if (num)
+                rtc_handle_legacy_irq(rtc, num, RTC_UF);
+}
+static void rtc_uie_timer(unsigned long data)
+{
+        struct rtc_device *rtc = (struct rtc_device *)data;
+        unsigned long flags;
+
+        spin_lock_irqsave(&rtc->irq_lock, flags);
+        rtc->uie_timer_active = 0;
+        rtc->uie_task_active = 1;
+        if ((schedule_work(&rtc->uie_task) == 0))
+                rtc->uie_task_active = 0;
+        spin_unlock_irqrestore(&rtc->irq_lock, flags);
+}
+
+static int clear_uie(struct rtc_device *rtc)
+{
+        spin_lock_irq(&rtc->irq_lock);
+        if (rtc->uie_irq_active) {
+                rtc->stop_uie_polling = 1;
+                if (rtc->uie_timer_active) {
+                        spin_unlock_irq(&rtc->irq_lock);
+                        del_timer_sync(&rtc->uie_timer);
+                        spin_lock_irq(&rtc->irq_lock);
+                        rtc->uie_timer_active = 0;
+                }
+                if (rtc->uie_task_active) {
+                        spin_unlock_irq(&rtc->irq_lock);
+                        flush_scheduled_work();
+                        spin_lock_irq(&rtc->irq_lock);
+                }
+                rtc->uie_irq_active = 0;
+        }
+        spin_unlock_irq(&rtc->irq_lock);
+        return 0;
+}
+
+static int set_uie(struct rtc_device *rtc)
+{
+        struct rtc_time tm;
+        int err;
+
+        err = rtc_read_time(rtc, &tm);
+        if (err)
+                return err;
+        spin_lock_irq(&rtc->irq_lock);
+        if (!rtc->uie_irq_active) {
+                rtc->uie_irq_active = 1;
+                rtc->stop_uie_polling = 0;
+                rtc->oldsecs = tm.tm_sec;
+                rtc->uie_task_active = 1;
+                if (schedule_work(&rtc->uie_task) == 0)
+                        rtc->uie_task_active = 0;
+        }
+        rtc->irq_data = 0;
+        spin_unlock_irq(&rtc->irq_lock);
+        return 0;
+}
+
+int rtc_dev_update_irq_enable_emul(struct rtc_device *rtc, unsigned int enabled)
+{
+        if (enabled)
+                return set_uie(rtc);
+        else
+                return clear_uie(rtc);
+}
+EXPORT_SYMBOL(rtc_dev_update_irq_enable_emul);
+
+#endif /* CONFIG_RTC_INTF_DEV_UIE_EMUL */
 
 static ssize_t
 rtc_dev_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
@@ -387,6 +486,11 @@ void rtc_dev_prepare(struct rtc_device *rtc)
 
         rtc->dev.devt = MKDEV(MAJOR(rtc_devt), rtc->id);
 
+#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
+        INIT_WORK(&rtc->uie_task, rtc_uie_task);
+        setup_timer(&rtc->uie_timer, rtc_uie_timer, (unsigned long)rtc);
+#endif
+
         cdev_init(&rtc->char_dev, &rtc_dev_fops);
         rtc->char_dev.owner = rtc->owner;
 }
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index a0b639f8e805..89c3e5182991 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -203,6 +203,18 @@ struct rtc_device
         struct hrtimer pie_timer; /* sub second exp, so needs hrtimer */
         int pie_enabled;
         struct work_struct irqwork;
+
+
+#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
+        struct work_struct uie_task;
+        struct timer_list uie_timer;
+        /* Those fields are protected by rtc->irq_lock */
+        unsigned int oldsecs;
+        unsigned int uie_irq_active:1;
+        unsigned int stop_uie_polling:1;
+        unsigned int uie_task_active:1;
+        unsigned int uie_timer_active:1;
+#endif
 };
 #define to_rtc_device(d) container_of(d, struct rtc_device, dev)
 
@@ -235,7 +247,10 @@ extern int rtc_irq_set_freq(struct rtc_device *rtc,
                                 struct rtc_task *task, int freq);
 extern int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled);
 extern int rtc_alarm_irq_enable(struct rtc_device *rtc, unsigned int enabled);
+extern int rtc_dev_update_irq_enable_emul(struct rtc_device *rtc,
+                                                unsigned int enabled);
 
+void rtc_handle_legacy_irq(struct rtc_device *rtc, int num, int mode);
 void rtc_aie_update_irq(void *private);
 void rtc_uie_update_irq(void *private);
 enum hrtimer_restart rtc_pie_update_irq(struct hrtimer *timer);