rtc: add boot_timesource sysfs attribute

CONFIG_RTC_HCTOSYS allows the kernel to read the system time from the RTC at boot and resume, avoiding the need for userspace to do so. Unfortunately userspace currently has no way to know whether this configuration option is enabled and thus cannot sensibly choose whether to run hwclock itself or not. Add a hctosys sysfs attribute which indicates whether a given RTC set the system clock. Signed-off-by: Matthew Garrett <[email protected]> Acked-by: Alessandro Zummo <[email protected]> Cc: Mark Brown <[email protected]> Cc: David Brownell <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
mna · Sep 23, 2009 · d8c1acb · d8c1acb
1 parent ea3d160
commit d8c1acb
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diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
@@ -143,6 +143,8 @@ rtc attributes without requiring the use of ioctls. All dates and times
 are in the RTC's timezone, rather than in system time.
 
 date:  	   	 RTC-provided date
+hctosys:   	 1 if the RTC provided the system time at boot via the
+		 CONFIG_RTC_HCTOSYS kernel option, 0 otherwise
 max_user_freq:	 The maximum interrupt rate an unprivileged user may request
 		 from this RTC.
 name:		 The name of the RTC corresponding to this sysfs directory

diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
@@ -102,13 +102,27 @@ rtc_sysfs_set_max_user_freq(struct device *dev, struct device_attribute *attr,
 	return n;
 }
 
+static ssize_t
+rtc_sysfs_show_hctosys(struct device *dev, struct device_attribute *attr,
+		char *buf)
+{
+#ifdef CONFIG_RTC_HCTOSYS_DEVICE
+	if (strcmp(dev_name(&to_rtc_device(dev)->dev),
+		   CONFIG_RTC_HCTOSYS_DEVICE) == 0)
+		return sprintf(buf, "1\n");
+	else
+#endif
+		return sprintf(buf, "0\n");
+}
+
 static struct device_attribute rtc_attrs[] = {
 	__ATTR(name, S_IRUGO, rtc_sysfs_show_name, NULL),
 	__ATTR(date, S_IRUGO, rtc_sysfs_show_date, NULL),
 	__ATTR(time, S_IRUGO, rtc_sysfs_show_time, NULL),
 	__ATTR(since_epoch, S_IRUGO, rtc_sysfs_show_since_epoch, NULL),
 	__ATTR(max_user_freq, S_IRUGO | S_IWUSR, rtc_sysfs_show_max_user_freq,
 			rtc_sysfs_set_max_user_freq),
+	__ATTR(hctosys, S_IRUGO, rtc_sysfs_show_hctosys, NULL),
 	{ },
 };