x86: Do full rtc synchronization with ntp

Every 11 minutes ntp attempts to update the x86 rtc with the current
system time.  Currently, the x86 code only updates the rtc if the system
time is within +/-15 minutes of the current value of the rtc. This
was done originally to avoid setting the RTC if the RTC was in localtime
mode (common with Windows dualbooting).  Other architectures do a full
synchronization and now that we have better infrastructure to detect
when the RTC is in localtime, there is no reason that x86 should be
software limited to a 30 minute window.

This patch changes the behavior of the kernel to do a full synchronization
(year, month, day, hour, minute, and second) of the rtc when ntp requests
a synchronization between the system time and the rtc.

I've used the RTC library functions in this patchset as they do all the
required bounds checking.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: x86@kernel.org
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: linux-efi@vger.kernel.org
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
[jstultz: Tweak commit message, fold in build fix found by fengguang
Also add select RTC_LIB to X86, per new dependency, as found by prarit]
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 12 insertions, 57 deletions

diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
index 2e8f3d3b5641..198eb201ed3b 100644
--- a/arch/x86/kernel/rtc.c
+++ b/arch/x86/kernel/rtc.c
@@ -13,6 +13,7 @@
 #include <asm/x86_init.h>
 #include <asm/time.h>
 #include <asm/mrst.h>
+#include <asm/rtc.h>
 
 #ifdef CONFIG_X86_32
 /*
@@ -36,70 +37,24 @@ EXPORT_SYMBOL(rtc_lock);
  * nowtime is written into the registers of the CMOS clock, it will
  * jump to the next second precisely 500 ms later. Check the Motorola
  * MC146818A or Dallas DS12887 data sheet for details.
- *
- * BUG: This routine does not handle hour overflow properly; it just
- *      sets the minutes. Usually you'll only notice that after reboot!
  */
 int mach_set_rtc_mmss(unsigned long nowtime)
 {
-        int real_seconds, real_minutes, cmos_minutes;
-        unsigned char save_control, save_freq_select;
-        unsigned long flags;
+        struct rtc_time tm;
         int retval = 0;
 
-        spin_lock_irqsave(&rtc_lock, flags);
-
-         /* tell the clock it's being set */
-        save_control = CMOS_READ(RTC_CONTROL);
-        CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
-
-        /* stop and reset prescaler */
-        save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
-        CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
-
-        cmos_minutes = CMOS_READ(RTC_MINUTES);
-        if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
-                cmos_minutes = bcd2bin(cmos_minutes);
-
-        /*
-         * since we're only adjusting minutes and seconds,
-         * don't interfere with hour overflow. This avoids
-         * messing with unknown time zones but requires your
-         * RTC not to be off by more than 15 minutes
-         */
-        real_seconds = nowtime % 60;
-        real_minutes = nowtime / 60;
-        /* correct for half hour time zone */
-        if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
-                real_minutes += 30;
-        real_minutes %= 60;
-
-        if (abs(real_minutes - cmos_minutes) < 30) {
-                if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
-                        real_seconds = bin2bcd(real_seconds);
-                        real_minutes = bin2bcd(real_minutes);
-                }
-                CMOS_WRITE(real_seconds, RTC_SECONDS);
-                CMOS_WRITE(real_minutes, RTC_MINUTES);
+        rtc_time_to_tm(nowtime, &tm);
+        if (!rtc_valid_tm(&tm)) {
+                retval = set_rtc_time(&tm);
+                if (retval)
+                        printk(KERN_ERR "%s: RTC write failed with error %d\n",
+                               __FUNCTION__, retval);
         } else {
-                printk_once(KERN_NOTICE
-                       "set_rtc_mmss: can't update from %d to %d\n",
-                       cmos_minutes, real_minutes);
-                retval = -1;
+                printk(KERN_ERR
+                       "%s: Invalid RTC value: write of %lx to RTC failed\n",
+                        __FUNCTION__, nowtime);
+                retval = -EINVAL;
         }
-
-        /* The following flags have to be released exactly in this order,
-         * otherwise the DS12887 (popular MC146818A clone with integrated
-         * battery and quartz) will not reset the oscillator and will not
-         * update precisely 500 ms later. You won't find this mentioned in
-         * the Dallas Semiconductor data sheets, but who believes data
-         * sheets anyway ...                           -- Markus Kuhn
-         */
-        CMOS_WRITE(save_control, RTC_CONTROL);
-        CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
-
-        spin_unlock_irqrestore(&rtc_lock, flags);
-
         return retval;
 }