Re: [rtc-linux] Re: [PATCH 2/2] rtc: Add boot_timesource sysfsattribute

From: Matthew Garrett
Date: Fri Sep 04 2009 - 13:09:42 EST

Ok. How's this?

commit 09895be2ef8528dc33ca8516ca4f5ccbec2ffb05
Author: Matthew Garrett <mjg@xxxxxxxxxx>
Date: Fri Sep 4 12:23:02 2009 -0400

rtc: Add hctosys 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 <mjg@xxxxxxxxxx>

diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
index 216bb8c..baac51f 100644
--- 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
index 2531ce4..7dd23a6 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -102,6 +102,19 @@ 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)
+ if (strcmp(dev_name(&to_rtc_device(dev)->dev),
+ return sprintf(buf, "1\n");
+ else
+ 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),
@@ -109,6 +122,7 @@ static struct device_attribute rtc_attrs[] = {
__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,
+ __ATTR(hctosys, S_IRUGO, rtc_sysfs_show_hctosys, NULL),
{ },

Matthew Garrett | mjg59@xxxxxxxxxxxxx
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