[PATCH v10 2/7] time: sync read_boot_clock64() with persistent clock

[Pavel Tatashin]

read_boot_clock64() returns a boot start timestamp from epoch. Some arches
may need to access the persistent clock interface in order to calculate the
epoch offset. The resolution of the persistent clock, however, might be
low.  Therefore, in order to avoid time discrepancies a new argument 'now'
is added to read_boot_clock64() parameters. Arch may decide to use it
instead of accessing persistent clock again.

Also, change read_boot_clock64() to have __init prototype since it is
accessed only during boot.

Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
 arch/arm/kernel/time.c      | 2 +-
 arch/s390/kernel/time.c     | 2 +-
 include/linux/timekeeping.h | 2 +-
 kernel/time/timekeeping.c   | 8 ++++++--
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/time.c b/arch/arm/kernel/time.c
index cf2701cb0de8..40fd2e036eef 100644
--- a/arch/arm/kernel/time.c
+++ b/arch/arm/kernel/time.c
@@ -90,7 +90,7 @@ void read_persistent_clock64(struct timespec64 *ts)
 	__read_persistent_clock(ts);
 }
 
-void read_boot_clock64(struct timespec64 *ts)
+void __init read_boot_clock64(struct timespec64 *now, struct timespec64 *ts)
 {
 	__read_boot_clock(ts);
 }
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index cf561160ea88..9b0c69e3d795 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -221,7 +221,7 @@ void read_persistent_clock64(struct timespec64 *ts)
 	ext_to_timespec64(clk, ts);
 }
 
-void read_boot_clock64(struct timespec64 *ts)
+void __init read_boot_clock64(struct timespec64 *now, struct timespec64 *ts)
 {
 	unsigned char clk[STORE_CLOCK_EXT_SIZE];
 	__u64 delta;
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 86bc2026efce..6b607e8bedfa 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -243,7 +243,7 @@ extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
 extern int persistent_clock_is_local;
 
 extern void read_persistent_clock64(struct timespec64 *ts);
-extern void read_boot_clock64(struct timespec64 *ts);
+extern void read_boot_clock64(struct timespec64 *now, struct timespec64 *ts);
 extern int update_persistent_clock64(struct timespec64 now);
 
 /*
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4786df904c22..fb6898fab374 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1502,9 +1502,13 @@ void __weak read_persistent_clock64(struct timespec64 *ts64)
  * Function to read the exact time the system has been started.
  * Returns a timespec64 with tv_sec=0 and tv_nsec=0 if unsupported.
  *
+ * Argument 'now' contains time from persistent clock to calculate offset from
+ * epoch. May contain zeros if persist ant clock is not available.
+ *
  *  XXX - Do be sure to remove it once all arches implement it.
  */
-void __weak read_boot_clock64(struct timespec64 *ts)
+void __weak __init read_boot_clock64(struct timespec64 *now,
+				     struct timespec64 *ts)
 {
 	ts->tv_sec = 0;
 	ts->tv_nsec = 0;
@@ -1535,7 +1539,7 @@ void __init timekeeping_init(void)
 	} else if (now.tv_sec || now.tv_nsec)
 		persistent_clock_exists = true;
 
-	read_boot_clock64(&boot);
+	read_boot_clock64(&now, &boot);
 	if (!timespec64_valid_strict(&boot)) {
 		pr_warn("WARNING: Boot clock returned invalid value!\n"
 			"         Check your CMOS/BIOS settings.\n");
-- 
2.17.1