rtc_hctosys expects RTCs in UTC (doc)

The RTC "hctosys" mechanism expects that RTC clock will use UTC, not local
time (e.g.  PST).  Say so in Kconfig and in the kernel message.

(Strictly speaking, the RTC clock should be tracking the POSIX epoch.  That's
not worth going into here.  Goofing timezones means clocks are wrong by many
hours; the POSIX-v-UTC differences just cost seconds.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 5 insertions, 3 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index cbde770eb121..7958635f12cc 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -36,7 +36,9 @@ config RTC_HCTOSYS_DEVICE
         help
           The RTC device that will be used to (re)initialize the system
           clock, usually rtc0.  Initialization is done when the system
-          starts up, and when it resumes from a low power state.
+          starts up, and when it resumes from a low power state.  This
+          device should record time in UTC, since the kernel won't do
+          timezone correction.
 
           The driver for this RTC device must be loaded before late_initcall
           functions run, so it must usually be statically linked.
diff --git a/drivers/rtc/hctosys.c b/drivers/rtc/hctosys.c
index 178527252c6a..33c0e98243ee 100644
--- a/drivers/rtc/hctosys.c
+++ b/drivers/rtc/hctosys.c
@@ -47,8 +47,8 @@ static int __init rtc_hctosys(void)
                         do_settimeofday(&tv);
 
                         dev_info(rtc->dev.parent,
-                                "setting the system clock to "
-                                "%d-%02d-%02d %02d:%02d:%02d (%u)\n",
+                                "setting system clock to "
+                                "%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
                                 tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
                                 tm.tm_hour, tm.tm_min, tm.tm_sec,
                                 (unsigned int) tv.tv_sec);