1 files changed, 101 insertions, 2 deletions

diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
index 2ddd0cf07140..899ab8c514fa 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -78,6 +78,92 @@ static struct attribute_group rtc_attr_group = {
         .attrs = rtc_attrs,
 };
 
+
+static ssize_t
+rtc_sysfs_show_wakealarm(struct class_device *dev, char *buf)
+{
+        ssize_t retval;
+        unsigned long alarm;
+        struct rtc_wkalrm alm;
+
+        /* Don't show disabled alarms; but the RTC could leave the
+         * alarm enabled after it's already triggered.  Alarms are
+         * conceptually one-shot, even though some common hardware
+         * (PCs) doesn't actually work that way.
+         *
+         * REVISIT maybe we should require RTC implementations to
+         * disable the RTC alarm after it triggers, for uniformity.
+         */
+        retval = rtc_read_alarm(dev, &alm);
+        if (retval == 0 && alm.enabled) {
+                rtc_tm_to_time(&alm.time, &alarm);
+                retval = sprintf(buf, "%lu\n", alarm);
+        }
+
+        return retval;
+}
+
+static ssize_t
+rtc_sysfs_set_wakealarm(struct class_device *dev, const char *buf, size_t n)
+{
+        ssize_t retval;
+        unsigned long now, alarm;
+        struct rtc_wkalrm alm;
+
+        /* Only request alarms that trigger in the future.  Disable them
+         * by writing another time, e.g. 0 meaning Jan 1 1970 UTC.
+         */
+        retval = rtc_read_time(dev, &alm.time);
+        if (retval < 0)
+                return retval;
+        rtc_tm_to_time(&alm.time, &now);
+
+        alarm = simple_strtoul(buf, NULL, 0);
+        if (alarm > now) {
+                /* Avoid accidentally clobbering active alarms; we can't
+                 * entirely prevent that here, without even the minimal
+                 * locking from the /dev/rtcN api.
+                 */
+                retval = rtc_read_alarm(dev, &alm);
+                if (retval < 0)
+                        return retval;
+                if (alm.enabled)
+                        return -EBUSY;
+
+                alm.enabled = 1;
+        } else {
+                alm.enabled = 0;
+
+                /* Provide a valid future alarm time.  Linux isn't EFI,
+                 * this time won't be ignored when disabling the alarm.
+                 */
+                alarm = now + 300;
+        }
+        rtc_time_to_tm(alarm, &alm.time);
+
+        retval = rtc_set_alarm(dev, &alm);
+        return (retval < 0) ? retval : n;
+}
+static const CLASS_DEVICE_ATTR(wakealarm, S_IRUGO | S_IWUSR,
+                rtc_sysfs_show_wakealarm, rtc_sysfs_set_wakealarm);
+
+
+/* The reason to trigger an alarm with no process watching it (via sysfs)
+ * is its side effect:  waking from a system state like suspend-to-RAM or
+ * suspend-to-disk.  So: no attribute unless that side effect is possible.
+ * (Userspace may disable that mechanism later.)
+ */
+static inline int rtc_does_wakealarm(struct class_device *class_dev)
+{
+        struct rtc_device *rtc;
+
+        if (!device_can_wakeup(class_dev->dev))
+                return 0;
+        rtc = to_rtc_device(class_dev);
+        return rtc->ops->set_alarm != NULL;
+}
+
+
 static int rtc_sysfs_add_device(struct class_device *class_dev,
                                         struct class_interface *class_intf)
 {
@@ -87,8 +173,18 @@ static int rtc_sysfs_add_device(struct class_device *class_dev,
 
         err = sysfs_create_group(&class_dev->kobj, &rtc_attr_group);
         if (err)
-                dev_err(class_dev->dev,
-                        "failed to create sysfs attributes\n");
+                dev_err(class_dev->dev, "failed to create %s\n",
+                                "sysfs attributes");
+        else if (rtc_does_wakealarm(class_dev)) {
+                /* not all RTCs support both alarms and wakeup */
+                err = class_device_create_file(class_dev,
+                                        &class_device_attr_wakealarm);
+                if (err) {
+                        dev_err(class_dev->dev, "failed to create %s\n",
+                                        "alarm attribute");
+                        sysfs_remove_group(&class_dev->kobj, &rtc_attr_group);
+                }
+        }
 
         return err;
 }
@@ -96,6 +192,9 @@ static int rtc_sysfs_add_device(struct class_device *class_dev,
 static void rtc_sysfs_remove_device(struct class_device *class_dev,
                                 struct class_interface *class_intf)
 {
+        if (rtc_does_wakealarm(class_dev))
+                class_device_remove_file(class_dev,
+                                &class_device_attr_wakealarm);
         sysfs_remove_group(&class_dev->kobj, &rtc_attr_group);
 }