[tip: timers/ptp] vdso: Introduce aux_clock_resolution_ns()

["tip-bot2 for Thomas Weißschuh" <tip-bot2@linutronix.de>]

The following commit has been merged into the timers/ptp branch of tip:

Commit-ID:     8361c5bf4965e5d091e0413c4aeeb2f9dad4278f
Gitweb:        https://git.kernel.org/tip/8361c5bf4965e5d091e0413c4aeeb2f9dad4278f
Author:        Thomas Weißschuh <thomas.weissschuh@linutronix.de>
AuthorDate:    Tue, 01 Jul 2025 10:58:04 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 07 Jul 2025 08:58:53 +02:00

vdso: Introduce aux_clock_resolution_ns()

Move the constant resolution to a shared header,
so the vDSO can use it and return it without going through a syscall.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250701-vdso-auxclock-v1-10-df7d9f87b9b8@linutronix.de

---
 include/vdso/auxclock.h   | 13 +++++++++++++
 kernel/time/timekeeping.c |  6 ++++--
 2 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 include/vdso/auxclock.h

diff --git a/include/vdso/auxclock.h b/include/vdso/auxclock.h
new file mode 100644
index 0000000..6d6e74c
--- /dev/null
+++ b/include/vdso/auxclock.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _VDSO_AUXCLOCK_H
+#define _VDSO_AUXCLOCK_H
+
+#include <uapi/linux/time.h>
+#include <uapi/linux/types.h>
+
+static __always_inline u64 aux_clock_resolution_ns(void)
+{
+	return 1;
+}
+
+#endif /* _VDSO_AUXCLOCK_H */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index c6fe89b..cbcf090 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -26,6 +26,8 @@
 #include <linux/audit.h>
 #include <linux/random.h>
 
+#include <vdso/auxclock.h>
+
 #include "tick-internal.h"
 #include "ntp_internal.h"
 #include "timekeeping_internal.h"
@@ -2876,8 +2878,8 @@ static int aux_get_res(clockid_t id, struct timespec64 *tp)
 	if (!clockid_aux_valid(id))
 		return -ENODEV;
 
-	tp->tv_sec = 0;
-	tp->tv_nsec = 1;
+	tp->tv_sec = aux_clock_resolution_ns() / NSEC_PER_SEC;
+	tp->tv_nsec = aux_clock_resolution_ns() % NSEC_PER_SEC;
 	return 0;
 }