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-rw-r--r--arch/powerpc/kernel/time.c68
1 files changed, 52 insertions, 16 deletions
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 476a527b220d..0cc0dad905d5 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -841,28 +841,66 @@ static notrace u64 timebase_read(struct clocksource *cs)
return (u64)get_tb();
}
-void update_vsyscall_old(struct timespec *wall_time, struct timespec *wtm,
- struct clocksource *clock, u32 mult, u64 cycle_last)
+
+void update_vsyscall(struct timekeeper *tk)
{
+ struct timespec xt;
+ struct clocksource *clock = tk->tkr_mono.clock;
+ u32 mult = tk->tkr_mono.mult;
+ u32 shift = tk->tkr_mono.shift;
+ u64 cycle_last = tk->tkr_mono.cycle_last;
u64 new_tb_to_xs, new_stamp_xsec;
- u32 frac_sec;
+ u64 frac_sec;
if (clock != &clocksource_timebase)
return;
+ xt.tv_sec = tk->xtime_sec;
+ xt.tv_nsec = (long)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);
+
/* Make userspace gettimeofday spin until we're done. */
++vdso_data->tb_update_count;
smp_mb();
- /* 19342813113834067 ~= 2^(20+64) / 1e9 */
- new_tb_to_xs = (u64) mult * (19342813113834067ULL >> clock->shift);
- new_stamp_xsec = (u64) wall_time->tv_nsec * XSEC_PER_SEC;
- do_div(new_stamp_xsec, 1000000000);
- new_stamp_xsec += (u64) wall_time->tv_sec * XSEC_PER_SEC;
+ /*
+ * This computes ((2^20 / 1e9) * mult) >> shift as a
+ * 0.64 fixed-point fraction.
+ * The computation in the else clause below won't overflow
+ * (as long as the timebase frequency is >= 1.049 MHz)
+ * but loses precision because we lose the low bits of the constant
+ * in the shift. Note that 19342813113834067 ~= 2^(20+64) / 1e9.
+ * For a shift of 24 the error is about 0.5e-9, or about 0.5ns
+ * over a second. (Shift values are usually 22, 23 or 24.)
+ * For high frequency clocks such as the 512MHz timebase clock
+ * on POWER[6789], the mult value is small (e.g. 32768000)
+ * and so we can shift the constant by 16 initially
+ * (295147905179 ~= 2^(20+64-16) / 1e9) and then do the
+ * remaining shifts after the multiplication, which gives a
+ * more accurate result (e.g. with mult = 32768000, shift = 24,
+ * the error is only about 1.2e-12, or 0.7ns over 10 minutes).
+ */
+ if (mult <= 62500000 && clock->shift >= 16)
+ new_tb_to_xs = ((u64) mult * 295147905179ULL) >> (clock->shift - 16);
+ else
+ new_tb_to_xs = (u64) mult * (19342813113834067ULL >> clock->shift);
+
+ /*
+ * Compute the fractional second in units of 2^-32 seconds.
+ * The fractional second is tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift
+ * in nanoseconds, so multiplying that by 2^32 / 1e9 gives
+ * it in units of 2^-32 seconds.
+ * We assume shift <= 32 because clocks_calc_mult_shift()
+ * generates shift values in the range 0 - 32.
+ */
+ frac_sec = tk->tkr_mono.xtime_nsec << (32 - shift);
+ do_div(frac_sec, NSEC_PER_SEC);
- BUG_ON(wall_time->tv_nsec >= NSEC_PER_SEC);
- /* this is tv_nsec / 1e9 as a 0.32 fraction */
- frac_sec = ((u64) wall_time->tv_nsec * 18446744073ULL) >> 32;
+ /*
+ * Work out new stamp_xsec value for any legacy users of systemcfg.
+ * stamp_xsec is in units of 2^-20 seconds.
+ */
+ new_stamp_xsec = frac_sec >> 12;
+ new_stamp_xsec += tk->xtime_sec * XSEC_PER_SEC;
/*
* tb_update_count is used to allow the userspace gettimeofday code
@@ -872,15 +910,13 @@ void update_vsyscall_old(struct timespec *wall_time, struct timespec *wtm,
* the two values of tb_update_count match and are even then the
* tb_to_xs and stamp_xsec values are consistent. If not, then it
* loops back and reads them again until this criteria is met.
- * We expect the caller to have done the first increment of
- * vdso_data->tb_update_count already.
*/
vdso_data->tb_orig_stamp = cycle_last;
vdso_data->stamp_xsec = new_stamp_xsec;
vdso_data->tb_to_xs = new_tb_to_xs;
- vdso_data->wtom_clock_sec = wtm->tv_sec;
- vdso_data->wtom_clock_nsec = wtm->tv_nsec;
- vdso_data->stamp_xtime = *wall_time;
+ vdso_data->wtom_clock_sec = tk->wall_to_monotonic.tv_sec;
+ vdso_data->wtom_clock_nsec = tk->wall_to_monotonic.tv_nsec;
+ vdso_data->stamp_xtime = xt;
vdso_data->stamp_sec_fraction = frac_sec;
smp_wmb();
++(vdso_data->tb_update_count);