Patchwork Re: [PATCH 2/2] rtc: Add boot_timesource sysfs attribute

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Submitter Matthew Garrett
Date Sept. 4, 2009, 5:09 p.m.
Message ID <20090904170928.GA26009@srcf.ucam.org>
Download mbox | patch
Permalink /patch/33006/
State Accepted
Headers show

Comments

Matthew Garrett - Sept. 4, 2009, 5:09 p.m.
Ok. How's this?

commit 09895be2ef8528dc33ca8516ca4f5ccbec2ffb05
Author: Matthew Garrett <mjg@redhat.com>
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@redhat.com>
Alessandro Zummo - Sept. 5, 2009, 9:11 p.m.
On Fri, 4 Sep 2009 18:09:28 +0100
Matthew Garrett <mjg59@srcf.ucam.org> wrote:

> Ok. How's this?
> 
> commit 09895be2ef8528dc33ca8516ca4f5ccbec2ffb05
> Author: Matthew Garrett <mjg@redhat.com>
> Date:   Fri Sep 4 12:23:02 2009 -0400

 perfect, ty.

 Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Mark Brown - Sept. 6, 2009, 1:34 a.m.
On Fri, Sep 04, 2009 at 06:09:28PM +0100, Matthew Garrett wrote:

> +hctosys:   	 1 if the RTC provided the system time at boot via the
> +		 CONFIG_RTC_HCTOSYS kernel option, 0 otherwise

...

> +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

Strictly speaking this only reports if the RTC was configured to provide
the system time at boot, it does not check to see if it actually
succeeded in doing so.  Obviously failures here are a relatively rare
occurrance but they can happen.  I don't think it's worth changing the
code since it's unlikely userspace will be able to do any better than
the kernel did but it might be worth updating the documentation just in
case.

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Patch

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)
+{
+#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),
 	{ },
 };