rtc: fix CMOS time error after writing /proc/acpi/alarm

When writing /proc/acpi/alarm in adjust mode, e.g.
	echo "+0000-00-00 00:00:15" >/proc/acpi/alarm
The "century" field should be read and added to "year" field before
writing, otherwise the CMOS time will go back to 2000 years ago, e.g.
	# cat /proc/acpi/alarm
	0008-06-21 11:38:46
Then the system time may be reset to the date of manufacture after
rebooting. This patch fixed this issue.

Signed-off-by: Huacai Chen <huacai.chen@intel.com>
Acked-by: Pavel Machek <pavel@suse.cz>
Acked-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/acpi/sleep/proc.c b/drivers/acpi/sleep/proc.c
index 224c57c03381..4ebbba2b6b19 100644
--- a/drivers/acpi/sleep/proc.c
+++ b/drivers/acpi/sleep/proc.c
@@ -315,8 +315,11 @@ acpi_system_write_alarm(struct file *file,
                 cmos_bcd_write(day, acpi_gbl_FADT.day_alarm, rtc_control);
         if (acpi_gbl_FADT.month_alarm)
                 cmos_bcd_write(mo, acpi_gbl_FADT.month_alarm, rtc_control);
-        if (acpi_gbl_FADT.century)
+        if (acpi_gbl_FADT.century) {
+                if (adjust)
+                        yr += cmos_bcd_read(acpi_gbl_FADT.century, rtc_control) * 100;
                 cmos_bcd_write(yr / 100, acpi_gbl_FADT.century, rtc_control);
+        }
         /* enable the rtc alarm interrupt */
         rtc_control |= RTC_AIE;
         CMOS_WRITE(rtc_control, RTC_CONTROL);