rtc: Add RTC range

Add a way for drivers to inform the core of the supported date/time range.
The core can then check whether the date/time or alarm is in the range
before calling ->set_time, ->set_mmss or ->set_alarm. It returns -ERANGE
when the time is out of range.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

4 files changed, 37 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-rtc b/Documentation/ABI/testing/sysfs-class-rtc
index 792a38300336..95984289a4ee 100644
--- a/Documentation/ABI/testing/sysfs-class-rtc
+++ b/Documentation/ABI/testing/sysfs-class-rtc
@@ -43,6 +43,14 @@ Contact:	linux-rtc@vger.kernel.org
 Description:
                 (RO) The name of the RTC corresponding to this sysfs directory
 
+What:           /sys/class/rtc/rtcX/range
+Date:           January 2018
+KernelVersion:  4.16
+Contact:        linux-rtc@vger.kernel.org
+Description:
+                Valid time range for the RTC, as seconds from epoch, formatted
+                as [min, max]
+
 What:           /sys/class/rtc/rtcX/since_epoch
 Date:           March 2006
 KernelVersion:  2.6.17
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 7e253be19ba7..c068daebeec2 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -70,6 +70,13 @@ int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
         if (err != 0)
                 return err;
 
+        if (rtc->range_min != rtc->range_max) {
+                time64_t time = rtc_tm_to_time64(tm);
+
+                if (time < rtc->range_min || time > rtc->range_max)
+                        return -ERANGE;
+        }
+
         err = mutex_lock_interruptible(&rtc->ops_lock);
         if (err)
                 return err;
@@ -374,6 +381,13 @@ int rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
         if (err != 0)
                 return err;
 
+        if (rtc->range_min != rtc->range_max) {
+                time64_t time = rtc_tm_to_time64(&alarm->time);
+
+                if (time < rtc->range_min || time > rtc->range_max)
+                        return -ERANGE;
+        }
+
         err = mutex_lock_interruptible(&rtc->ops_lock);
         if (err)
                 return err;
diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
index 92ff2edb86a6..454da38c6012 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -248,6 +248,14 @@ offset_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(offset);
 
+static ssize_t
+range_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+        return sprintf(buf, "[%lld,%llu]\n", to_rtc_device(dev)->range_min,
+                       to_rtc_device(dev)->range_max);
+}
+static DEVICE_ATTR_RO(range);
+
 static struct attribute *rtc_attrs[] = {
         &dev_attr_name.attr,
         &dev_attr_date.attr,
@@ -257,6 +265,7 @@ static struct attribute *rtc_attrs[] = {
         &dev_attr_hctosys.attr,
         &dev_attr_wakealarm.attr,
         &dev_attr_offset.attr,
+        &dev_attr_range.attr,
         NULL,
 };
 
@@ -286,6 +295,9 @@ static umode_t rtc_attr_is_visible(struct kobject *kobj,
         } else if (attr == &dev_attr_offset.attr) {
                 if (!rtc->ops->set_offset)
                         mode = 0;
+        } else if (attr == &dev_attr_range.attr) {
+                if (!(rtc->range_max - rtc->range_min))
+                        mode = 0;
         }
 
         return mode;
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 3b65b201169c..c78528c394e5 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -150,6 +150,9 @@ struct rtc_device {
         bool nvram_old_abi;
         struct bin_attribute *nvram;
 
+        time64_t range_min;
+        timeu64_t range_max;
+
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
         struct work_struct uie_task;
         struct timer_list uie_timer;