s390/time: convert tod_clock_base to union

Convert tod_clock_base to union tod_clock. This simplifies quite a bit
of code and also fixes a bug in read_persistent_clock64();

void read_persistent_clock64(struct timespec64 *ts)
{
        __u64 delta;

        delta = initial_leap_seconds + TOD_UNIX_EPOCH;
        get_tod_clock_ext(clk);
        *(__u64 *) &clk[1] -= delta;
        if (*(__u64 *) &clk[1] > delta)
                clk[0]--;
        ext_to_timespec64(clk, ts);
}

Assume &clk[1] == 3 and delta == 2; then after the substraction the if
condition becomes true and the epoch part of the clock is decremented
by one because of an assumed overflow, even though there is none.

Fix this by using 128 bit arithmetics and let the compiler do the
right thing:

void read_persistent_clock64(struct timespec64 *ts)
{
        union tod_clock clk;
        u64 delta;

        delta = initial_leap_seconds + TOD_UNIX_EPOCH;
        store_tod_clock_ext(&clk);
        clk.eitod -= delta;
        ext_to_timespec64(&clk, ts);
}

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 17 insertions, 33 deletions

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index c59cb44fbb7d..06bcfa636638 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -55,11 +55,7 @@
 #include <asm/cio.h>
 #include "entry.h"
 
-unsigned char tod_clock_base[16] __aligned(8) = {
-	/* Force to data section. */
-	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
-};
+union tod_clock tod_clock_base __section(".data");
 EXPORT_SYMBOL_GPL(tod_clock_base);
 
 u64 clock_comparator_max = -1ULL;
@@ -86,7 +82,7 @@ void __init time_early_init(void)
 	struct ptff_qui qui;
 
 	/* Initialize TOD steering parameters */
-	tod_steering_end = *(unsigned long long *) &tod_clock_base[1];
+	tod_steering_end = tod_clock_base.tod;
 	vdso_data->arch_data.tod_steering_end = tod_steering_end;
 
 	if (!test_facility(28))
@@ -113,18 +109,13 @@ unsigned long long notrace sched_clock(void)
 }
 NOKPROBE_SYMBOL(sched_clock);
 
-static void ext_to_timespec64(unsigned char *clk, struct timespec64 *xt)
+static void ext_to_timespec64(union tod_clock *clk, struct timespec64 *xt)
 {
-	unsigned long long high, low, rem, sec, nsec;
+	unsigned long rem, sec, nsec;
 
-	/* Split extendnd TOD clock to micro-seconds and sub-micro-seconds */
-	high = (*(unsigned long long *) clk) >> 4;
-	low = (*(unsigned long long *)&clk[7]) << 4;
-	/* Calculate seconds and nano-seconds */
-	sec = high;
+	sec = clk->us;
 	rem = do_div(sec, 1000000);
-	nsec = (((low >> 32) + (rem << 32)) * 1000) >> 32;
-
+	nsec = ((clk->sus + (rem << 12)) * 125) >> 9;
 	xt->tv_sec = sec;
 	xt->tv_nsec = nsec;
 }
@@ -204,30 +195,26 @@ static void stp_reset(void);
 
 void read_persistent_clock64(struct timespec64 *ts)
 {
-	unsigned char clk[STORE_CLOCK_EXT_SIZE];
-	__u64 delta;
+	union tod_clock clk;
+	u64 delta;
 
 	delta = initial_leap_seconds + TOD_UNIX_EPOCH;
-	get_tod_clock_ext(clk);
-	*(__u64 *) &clk[1] -= delta;
-	if (*(__u64 *) &clk[1] > delta)
-		clk[0]--;
-	ext_to_timespec64(clk, ts);
+	store_tod_clock_ext(&clk);
+	clk.eitod -= delta;
+	ext_to_timespec64(&clk, ts);
 }
 
 void __init read_persistent_wall_and_boot_offset(struct timespec64 *wall_time,
 						 struct timespec64 *boot_offset)
 {
-	unsigned char clk[STORE_CLOCK_EXT_SIZE];
 	struct timespec64 boot_time;
-	__u64 delta;
+	union tod_clock clk;
+	u64 delta;
 
 	delta = initial_leap_seconds + TOD_UNIX_EPOCH;
-	memcpy(clk, tod_clock_base, STORE_CLOCK_EXT_SIZE);
-	*(__u64 *)&clk[1] -= delta;
-	if (*(__u64 *)&clk[1] > delta)
-		clk[0]--;
-	ext_to_timespec64(clk, &boot_time);
+	clk = tod_clock_base;
+	clk.eitod -= delta;
+	ext_to_timespec64(&clk, &boot_time);
 
 	read_persistent_clock64(wall_time);
 	*boot_offset = timespec64_sub(*wall_time, boot_time);
@@ -381,10 +368,7 @@ static void clock_sync_global(unsigned long long delta)
 	struct ptff_qto qto;
 
 	/* Fixup the monotonic sched clock. */
-	*(unsigned long long *) &tod_clock_base[1] += delta;
-	if (*(unsigned long long *) &tod_clock_base[1] < delta)
-		/* Epoch overflow */
-		tod_clock_base[0]++;
+	tod_clock_base.eitod += delta;
 	/* Adjust TOD steering parameters. */
 	now = get_tod_clock();
 	adj = tod_steering_end - now;