powerpc: Keep xtime and gettimeofday in sync

This fixes a regression which was introduced by moving ppc32 to use
the same sort of lockless gettimeofday as ppc64 has been using for
some time.  This involves getting the timebase and performing some
simple arithmetic to convert it to seconds and microseconds.  However,
the factor and offset used there weren't being updated when NTP
varied the tick length using adjtimex.  64-bit didn't notice the
problem because it had a hook in the 32-bit adjtimex compat routine
that attempted to work out what the generic timekeeping code would
do and alter the factor and offset to match.  However, that code
was very complex and it wasn't clear that it still matched what the
generic code would do.

Now we use the generic current_tick_length() routine that was recently
added to check that the current tick will be as long as we expect; if
not we recompute the factor and offset.  This keeps gettimeofday and
xtime in sync.  In addition we check that gettimeofday hasn't got ahead
of xtime on each timer interrupt; if it has, we resync.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 99 insertions, 183 deletions

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 1886045a2fd8..2a7ddc579379 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -50,6 +50,7 @@
 #include <linux/security.h>
 #include <linux/percpu.h>
 #include <linux/rtc.h>
+#include <linux/jiffies.h>
 
 #include <asm/io.h>
 #include <asm/processor.h>
@@ -99,7 +100,15 @@ EXPORT_SYMBOL(tb_ticks_per_usec);
 unsigned long tb_ticks_per_sec;
 u64 tb_to_xs;
 unsigned tb_to_us;
-unsigned long processor_freq;
+
+#define TICKLEN_SCALE   (SHIFT_SCALE - 10)
+u64 last_tick_len;      /* units are ns / 2^TICKLEN_SCALE */
+u64 ticklen_to_xs;      /* 0.64 fraction */
+
+/* If last_tick_len corresponds to about 1/HZ seconds, then
+   last_tick_len << TICKLEN_SHIFT will be about 2^63. */
+#define TICKLEN_SHIFT   (63 - 30 - TICKLEN_SCALE + SHIFT_HZ)
+
 DEFINE_SPINLOCK(rtc_lock);
 EXPORT_SYMBOL_GPL(rtc_lock);
 
@@ -113,10 +122,6 @@ extern unsigned long wall_jiffies;
 extern struct timezone sys_tz;
 static long timezone_offset;
 
-void ppc_adjtimex(void);
-
-static unsigned adjusting_time = 0;
-
 unsigned long ppc_proc_freq;
 unsigned long ppc_tb_freq;
 
@@ -178,8 +183,7 @@ static __inline__ void timer_check_rtc(void)
          */
         if (ppc_md.set_rtc_time && ntp_synced() &&
             xtime.tv_sec - last_rtc_update >= 659 &&
-            abs((xtime.tv_nsec/1000) - (1000000-1000000/HZ)) < 500000/HZ &&
-            jiffies - wall_jiffies == 1) {
+            abs((xtime.tv_nsec/1000) - (1000000-1000000/HZ)) < 500000/HZ) {
                 struct rtc_time tm;
                 to_tm(xtime.tv_sec + 1 + timezone_offset, &tm);
                 tm.tm_year -= 1900;
@@ -226,15 +230,14 @@ void do_gettimeofday(struct timeval *tv)
         if (__USE_RTC()) {
                 /* do this the old way */
                 unsigned long flags, seq;
-                unsigned int sec, nsec, usec, lost;
+                unsigned int sec, nsec, usec;
 
                 do {
                         seq = read_seqbegin_irqsave(&xtime_lock, flags);
                         sec = xtime.tv_sec;
                         nsec = xtime.tv_nsec + tb_ticks_since(tb_last_stamp);
-                        lost = jiffies - wall_jiffies;
                 } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
-                usec = nsec / 1000 + lost * (1000000 / HZ);
+                usec = nsec / 1000;
                 while (usec >= 1000000) {
                         usec -= 1000000;
                         ++sec;
@@ -248,23 +251,6 @@ void do_gettimeofday(struct timeval *tv)
 
 EXPORT_SYMBOL(do_gettimeofday);
 
-/* Synchronize xtime with do_gettimeofday */ 
-
-static inline void timer_sync_xtime(unsigned long cur_tb)
-{
-#ifdef CONFIG_PPC64
-        /* why do we do this? */
-        struct timeval my_tv;
-
-        __do_gettimeofday(&my_tv, cur_tb);
-
-        if (xtime.tv_sec <= my_tv.tv_sec) {
-                xtime.tv_sec = my_tv.tv_sec;
-                xtime.tv_nsec = my_tv.tv_usec * 1000;
-        }
-#endif
-}
-
 /*
  * There are two copies of tb_to_xs and stamp_xsec so that no
  * lock is needed to access and use these values in
@@ -323,15 +309,30 @@ static __inline__ void timer_recalc_offset(u64 cur_tb)
 {
         unsigned long offset;
         u64 new_stamp_xsec;
+        u64 tlen, t2x;
 
         if (__USE_RTC())
                 return;
+        tlen = current_tick_length();
         offset = cur_tb - do_gtod.varp->tb_orig_stamp;
-        if ((offset & 0x80000000u) == 0)
-                return;
-        new_stamp_xsec = do_gtod.varp->stamp_xsec
-                + mulhdu(offset, do_gtod.varp->tb_to_xs);
-        update_gtod(cur_tb, new_stamp_xsec, do_gtod.varp->tb_to_xs);
+        if (tlen == last_tick_len && offset < 0x80000000u) {
+                /* check that we're still in sync; if not, resync */
+                struct timeval tv;
+                __do_gettimeofday(&tv, cur_tb);
+                if (tv.tv_sec <= xtime.tv_sec &&
+                    (tv.tv_sec < xtime.tv_sec ||
+                     tv.tv_usec * 1000 <= xtime.tv_nsec))
+                        return;
+        }
+        if (tlen != last_tick_len) {
+                t2x = mulhdu(tlen << TICKLEN_SHIFT, ticklen_to_xs);
+                last_tick_len = tlen;
+        } else
+                t2x = do_gtod.varp->tb_to_xs;
+        new_stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
+        do_div(new_stamp_xsec, 1000000000);
+        new_stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
+        update_gtod(cur_tb, new_stamp_xsec, t2x);
 }
 
 #ifdef CONFIG_SMP
@@ -462,13 +463,10 @@ void timer_interrupt(struct pt_regs * regs)
                 write_seqlock(&xtime_lock);
                 tb_last_jiffy += tb_ticks_per_jiffy;
                 tb_last_stamp = per_cpu(last_jiffy, cpu);
-                timer_recalc_offset(tb_last_jiffy);
                 do_timer(regs);
-                timer_sync_xtime(tb_last_jiffy);
+                timer_recalc_offset(tb_last_jiffy);
                 timer_check_rtc();
                 write_sequnlock(&xtime_lock);
-                if (adjusting_time && (time_adjust == 0))
-                        ppc_adjtimex();
         }
         
         next_dec = tb_ticks_per_jiffy - ticks;
@@ -492,16 +490,18 @@ void timer_interrupt(struct pt_regs * regs)
 
 void wakeup_decrementer(void)
 {
-        int i;
+        unsigned long ticks;
 
-        set_dec(tb_ticks_per_jiffy);
         /*
-         * We don't expect this to be called on a machine with a 601,
-         * so using get_tbl is fine.
+         * The timebase gets saved on sleep and restored on wakeup,
+         * so all we need to do is to reset the decrementer.
          */
-        tb_last_stamp = tb_last_jiffy = get_tb();
-        for_each_cpu(i)
-                per_cpu(last_jiffy, i) = tb_last_stamp;
+        ticks = tb_ticks_since(__get_cpu_var(last_jiffy));
+        if (ticks < tb_ticks_per_jiffy)
+                ticks = tb_ticks_per_jiffy - ticks;
+        else
+                ticks = 1;
+        set_dec(ticks);
 }
 
 #ifdef CONFIG_SMP
@@ -541,8 +541,8 @@ int do_settimeofday(struct timespec *tv)
         time_t wtm_sec, new_sec = tv->tv_sec;
         long wtm_nsec, new_nsec = tv->tv_nsec;
         unsigned long flags;
-        long int tb_delta;
-        u64 new_xsec, tb_delta_xs;
+        u64 new_xsec;
+        unsigned long tb_delta;
 
         if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
                 return -EINVAL;
@@ -563,9 +563,19 @@ int do_settimeofday(struct timespec *tv)
                 first_settimeofday = 0;
         }
 #endif
+
+        /*
+         * Subtract off the number of nanoseconds since the
+         * beginning of the last tick.
+         * Note that since we don't increment jiffies_64 anywhere other
+         * than in do_timer (since we don't have a lost tick problem),
+         * wall_jiffies will always be the same as jiffies,
+         * and therefore the (jiffies - wall_jiffies) computation
+         * has been removed.
+         */
         tb_delta = tb_ticks_since(tb_last_stamp);
-        tb_delta += (jiffies - wall_jiffies) * tb_ticks_per_jiffy;
-        tb_delta_xs = mulhdu(tb_delta, do_gtod.varp->tb_to_xs);
+        tb_delta = mulhdu(tb_delta, do_gtod.varp->tb_to_xs); /* in xsec */
+        new_nsec -= SCALE_XSEC(tb_delta, 1000000000);
 
         wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - new_sec);
         wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - new_nsec);
@@ -580,12 +590,12 @@ int do_settimeofday(struct timespec *tv)
 
         ntp_clear();
 
-        new_xsec = 0;
-        if (new_nsec != 0) {
-                new_xsec = (u64)new_nsec * XSEC_PER_SEC;
+        new_xsec = xtime.tv_nsec;
+        if (new_xsec != 0) {
+                new_xsec *= XSEC_PER_SEC;
                 do_div(new_xsec, NSEC_PER_SEC);
         }
-        new_xsec += (u64)new_sec * XSEC_PER_SEC - tb_delta_xs;
+        new_xsec += (u64)xtime.tv_sec * XSEC_PER_SEC;
         update_gtod(tb_last_jiffy, new_xsec, do_gtod.varp->tb_to_xs);
 
         vdso_data->tz_minuteswest = sys_tz.tz_minuteswest;
@@ -671,7 +681,7 @@ void __init time_init(void)
         unsigned long flags;
         unsigned long tm = 0;
         struct div_result res;
-        u64 scale;
+        u64 scale, x;
         unsigned shift;
 
         if (ppc_md.time_init != NULL)
@@ -693,11 +703,36 @@ void __init time_init(void)
         }
 
         tb_ticks_per_jiffy = ppc_tb_freq / HZ;
-        tb_ticks_per_sec = tb_ticks_per_jiffy * HZ;
+        tb_ticks_per_sec = ppc_tb_freq;
         tb_ticks_per_usec = ppc_tb_freq / 1000000;
         tb_to_us = mulhwu_scale_factor(ppc_tb_freq, 1000000);
-        div128_by_32(1024*1024, 0, tb_ticks_per_sec, &res);
-        tb_to_xs = res.result_low;
+
+        /*
+         * Calculate the length of each tick in ns.  It will not be
+         * exactly 1e9/HZ unless ppc_tb_freq is divisible by HZ.
+         * We compute 1e9 * tb_ticks_per_jiffy / ppc_tb_freq,
+         * rounded up.
+         */
+        x = (u64) NSEC_PER_SEC * tb_ticks_per_jiffy + ppc_tb_freq - 1;
+        do_div(x, ppc_tb_freq);
+        tick_nsec = x;
+        last_tick_len = x << TICKLEN_SCALE;
+
+        /*
+         * Compute ticklen_to_xs, which is a factor which gets multiplied
+         * by (last_tick_len << TICKLEN_SHIFT) to get a tb_to_xs value.
+         * It is computed as:
+         * ticklen_to_xs = 2^N / (tb_ticks_per_jiffy * 1e9)
+         * where N = 64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT
+         * so as to give the result as a 0.64 fixed-point fraction.
+         */
+        div128_by_32(1ULL << (64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT), 0,
+                     tb_ticks_per_jiffy, &res);
+        div128_by_32(res.result_high, res.result_low, NSEC_PER_SEC, &res);
+        ticklen_to_xs = res.result_low;
+
+        /* Compute tb_to_xs from tick_nsec */
+        tb_to_xs = mulhdu(last_tick_len << TICKLEN_SHIFT, ticklen_to_xs);
 
         /*
          * Compute scale factor for sched_clock.
@@ -724,6 +759,14 @@ void __init time_init(void)
                 tm = get_boot_time();
 
         write_seqlock_irqsave(&xtime_lock, flags);
+
+        /* If platform provided a timezone (pmac), we correct the time */
+        if (timezone_offset) {
+                sys_tz.tz_minuteswest = -timezone_offset / 60;
+                sys_tz.tz_dsttime = 0;
+                tm -= timezone_offset;
+        }
+
         xtime.tv_sec = tm;
         xtime.tv_nsec = 0;
         do_gtod.varp = &do_gtod.vars[0];
@@ -738,18 +781,11 @@ void __init time_init(void)
         vdso_data->tb_orig_stamp = tb_last_jiffy;
         vdso_data->tb_update_count = 0;
         vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
-        vdso_data->stamp_xsec = xtime.tv_sec * XSEC_PER_SEC;
+        vdso_data->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
         vdso_data->tb_to_xs = tb_to_xs;
 
         time_freq = 0;
 
-        /* If platform provided a timezone (pmac), we correct the time */
-        if (timezone_offset) {
-                sys_tz.tz_minuteswest = -timezone_offset / 60;
-                sys_tz.tz_dsttime = 0;
-                xtime.tv_sec -= timezone_offset;
-        }
-
         last_rtc_update = xtime.tv_sec;
         set_normalized_timespec(&wall_to_monotonic,
                                 -xtime.tv_sec, -xtime.tv_nsec);
@@ -759,126 +795,6 @@ void __init time_init(void)
         set_dec(tb_ticks_per_jiffy);
 }
 
-/* 
- * After adjtimex is called, adjust the conversion of tb ticks
- * to microseconds to keep do_gettimeofday synchronized 
- * with ntpd.
- *
- * Use the time_adjust, time_freq and time_offset computed by adjtimex to 
- * adjust the frequency.
- */
-
-/* #define DEBUG_PPC_ADJTIMEX 1 */
-
-void ppc_adjtimex(void)
-{
-#ifdef CONFIG_PPC64
-        unsigned long den, new_tb_ticks_per_sec, tb_ticks, old_xsec,
-                new_tb_to_xs, new_xsec, new_stamp_xsec;
-        unsigned long tb_ticks_per_sec_delta;
-        long delta_freq, ltemp;
-        struct div_result divres; 
-        unsigned long flags;
-        long singleshot_ppm = 0;
-
-        /*
-         * Compute parts per million frequency adjustment to
-         * accomplish the time adjustment implied by time_offset to be
-         * applied over the elapsed time indicated by time_constant.
-         * Use SHIFT_USEC to get it into the same units as
-         * time_freq.
-         */
-        if ( time_offset < 0 ) {
-                ltemp = -time_offset;
-                ltemp <<= SHIFT_USEC - SHIFT_UPDATE;
-                ltemp >>= SHIFT_KG + time_constant;
-                ltemp = -ltemp;
-        } else {
-                ltemp = time_offset;
-                ltemp <<= SHIFT_USEC - SHIFT_UPDATE;
-                ltemp >>= SHIFT_KG + time_constant;
-        }
-        
-        /* If there is a single shot time adjustment in progress */
-        if ( time_adjust ) {
-#ifdef DEBUG_PPC_ADJTIMEX
-                printk("ppc_adjtimex: ");
-                if ( adjusting_time == 0 )
-                        printk("starting ");
-                printk("single shot time_adjust = %ld\n", time_adjust);
-#endif  
-        
-                adjusting_time = 1;
-                
-                /*
-                 * Compute parts per million frequency adjustment
-                 * to match time_adjust
-                 */
-                singleshot_ppm = tickadj * HZ;  
-                /*
-                 * The adjustment should be tickadj*HZ to match the code in
-                 * linux/kernel/timer.c, but experiments show that this is too
-                 * large. 3/4 of tickadj*HZ seems about right
-                 */
-                singleshot_ppm -= singleshot_ppm / 4;
-                /* Use SHIFT_USEC to get it into the same units as time_freq */
-                singleshot_ppm <<= SHIFT_USEC;
-                if ( time_adjust < 0 )
-                        singleshot_ppm = -singleshot_ppm;
-        }
-        else {
-#ifdef DEBUG_PPC_ADJTIMEX
-                if ( adjusting_time )
-                        printk("ppc_adjtimex: ending single shot time_adjust\n");
-#endif
-                adjusting_time = 0;
-        }
-        
-        /* Add up all of the frequency adjustments */
-        delta_freq = time_freq + ltemp + singleshot_ppm;
-        
-        /*
-         * Compute a new value for tb_ticks_per_sec based on
-         * the frequency adjustment
-         */
-        den = 1000000 * (1 << (SHIFT_USEC - 8));
-        if ( delta_freq < 0 ) {
-                tb_ticks_per_sec_delta = ( tb_ticks_per_sec * ( (-delta_freq) >> (SHIFT_USEC - 8))) / den;
-                new_tb_ticks_per_sec = tb_ticks_per_sec + tb_ticks_per_sec_delta;
-        }
-        else {
-                tb_ticks_per_sec_delta = ( tb_ticks_per_sec * ( delta_freq >> (SHIFT_USEC - 8))) / den;
-                new_tb_ticks_per_sec = tb_ticks_per_sec - tb_ticks_per_sec_delta;
-        }
-        
-#ifdef DEBUG_PPC_ADJTIMEX
-        printk("ppc_adjtimex: ltemp = %ld, time_freq = %ld, singleshot_ppm = %ld\n", ltemp, time_freq, singleshot_ppm);
-        printk("ppc_adjtimex: tb_ticks_per_sec - base = %ld  new = %ld\n", tb_ticks_per_sec, new_tb_ticks_per_sec);
-#endif
-
-        /*
-         * Compute a new value of tb_to_xs (used to convert tb to
-         * microseconds) and a new value of stamp_xsec which is the
-         * time (in 1/2^20 second units) corresponding to
-         * tb_orig_stamp.  This new value of stamp_xsec compensates
-         * for the change in frequency (implied by the new tb_to_xs)
-         * which guarantees that the current time remains the same.
-         */
-        write_seqlock_irqsave( &xtime_lock, flags );
-        tb_ticks = get_tb() - do_gtod.varp->tb_orig_stamp;
-        div128_by_32(1024*1024, 0, new_tb_ticks_per_sec, &divres);
-        new_tb_to_xs = divres.result_low;
-        new_xsec = mulhdu(tb_ticks, new_tb_to_xs);
-
-        old_xsec = mulhdu(tb_ticks, do_gtod.varp->tb_to_xs);
-        new_stamp_xsec = do_gtod.varp->stamp_xsec + old_xsec - new_xsec;
-
-        update_gtod(do_gtod.varp->tb_orig_stamp, new_stamp_xsec, new_tb_to_xs);
-
-        write_sequnlock_irqrestore( &xtime_lock, flags );
-#endif /* CONFIG_PPC64 */
-}
-
 
 #define FEBRUARY        2
 #define STARTOFTIME     1970