ia64: Update fsyscall gettime to use modern vsyscall_update

John Stultz provided the outline for this patch back in May 2014 here:

	http://patches.linaro.org/patch/30501/

but I let this sit on the shelf for too long and in the intervening
years almost every field in "struct timekeeper" was changed. So this
is almost completely different from his original. Though the key change
in arch/ia64/kernel/fsys.S remains the same.

The core logic change with the updated vsyscall method is that we
preserve the base nanosecond value in shifted nanoseconds, which
allows us to avoid truncating and rounding up to the next nanosecond
every tick to avoid inconsistencies.

Thus the logic moved from
nsec = ((cycle_delta * mult)>>shift) + base_nsec;
to
nsec = ((cycle_delta * mult) + base_snsec) >> shift;

Cc: John Stultz <john.stultz@linaro.org>
Cc: linux-ia64@vger.kernel.org
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 21 insertions, 19 deletions

diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
index aa7be020a904..c6ecb97151a2 100644
--- a/arch/ia64/kernel/time.c
+++ b/arch/ia64/kernel/time.c
@@ -430,30 +430,32 @@ void update_vsyscall_tz(void)
 {
 }
 
-void update_vsyscall_old(struct timespec *wall, struct timespec *wtm,
-			 struct clocksource *c, u32 mult, u64 cycle_last)
+void update_vsyscall(struct timekeeper *tk)
 {
 	write_seqcount_begin(&fsyscall_gtod_data.seq);
 
-        /* copy fsyscall clock data */
-        fsyscall_gtod_data.clk_mask = c->mask;
-        fsyscall_gtod_data.clk_mult = mult;
-        fsyscall_gtod_data.clk_shift = c->shift;
-        fsyscall_gtod_data.clk_fsys_mmio = c->archdata.fsys_mmio;
-        fsyscall_gtod_data.clk_cycle_last = cycle_last;
-
-	/* copy kernel time structures */
-        fsyscall_gtod_data.wall_time.tv_sec = wall->tv_sec;
-        fsyscall_gtod_data.wall_time.tv_nsec = wall->tv_nsec;
-	fsyscall_gtod_data.monotonic_time.tv_sec = wtm->tv_sec
-							+ wall->tv_sec;
-	fsyscall_gtod_data.monotonic_time.tv_nsec = wtm->tv_nsec
-							+ wall->tv_nsec;
+	/* copy vsyscall data */
+	fsyscall_gtod_data.clk_mask = tk->tkr_mono.mask;
+	fsyscall_gtod_data.clk_mult = tk->tkr_mono.mult;
+	fsyscall_gtod_data.clk_shift = tk->tkr_mono.shift;
+	fsyscall_gtod_data.clk_fsys_mmio = tk->tkr_mono.clock->archdata.fsys_mmio;
+	fsyscall_gtod_data.clk_cycle_last = tk->tkr_mono.cycle_last;
+
+	fsyscall_gtod_data.wall_time.sec = tk->xtime_sec;
+	fsyscall_gtod_data.wall_time.snsec = tk->tkr_mono.xtime_nsec;
+
+	fsyscall_gtod_data.monotonic_time.sec = tk->xtime_sec
+					      + tk->wall_to_monotonic.tv_sec;
+	fsyscall_gtod_data.monotonic_time.snsec = tk->tkr_mono.xtime_nsec
+						+ ((u64)tk->wall_to_monotonic.tv_nsec
+							<< tk->tkr_mono.shift);
 
 	/* normalize */
-	while (fsyscall_gtod_data.monotonic_time.tv_nsec >= NSEC_PER_SEC) {
-		fsyscall_gtod_data.monotonic_time.tv_nsec -= NSEC_PER_SEC;
-		fsyscall_gtod_data.monotonic_time.tv_sec++;
+	while (fsyscall_gtod_data.monotonic_time.snsec >=
+					(((u64)NSEC_PER_SEC) << tk->tkr_mono.shift)) {
+		fsyscall_gtod_data.monotonic_time.snsec -=
+					((u64)NSEC_PER_SEC) << tk->tkr_mono.shift;
+		fsyscall_gtod_data.monotonic_time.sec++;
 	}
 
 	write_seqcount_end(&fsyscall_gtod_data.seq);