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 <mjg@redhat.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
index 2745e8197fde57f99383d22cecd06152a5e6d076..9104c10620840fcc45c47938a1b96dea48309aa7 100644 (file)
--- 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 2531ce4c9db082d94cd3b1afba7ac7f4acf93f85..7dd23a6fc8256954b384bfa027e81987e3dd2e29 100644 (file)
--- 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)
+{
+#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),
@@ -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,
                        rtc_sysfs_set_max_user_freq),
+       __ATTR(hctosys, S_IRUGO, rtc_sysfs_show_hctosys, NULL),
        { },
 };