time: Introduce auxiliary POSIX clocks

To support auxiliary timekeeping and the related user space interfaces,
it's required to define a clock ID range for them.

Reserve 8 auxiliary clock IDs after the regular timekeeping clock ID space.

This is the maximum number of auxiliary clocks the kernel can support. The actual
number of supported clocks depends obviously on the presence of related devices
and might be constraint by the available VDSO space.

Add the corresponding timekeeper IDs as well.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250519083025.905800695@linutronix.de

1 files changed, 11 insertions, 0 deletions

diff --git a/include/uapi/linux/time.h b/include/uapi/linux/time.h
index 4f4b6e48e01c..16ca1ac206fd 100644
--- a/include/uapi/linux/time.h
+++ b/include/uapi/linux/time.h
@@ -64,6 +64,17 @@ struct timezone {
 #define CLOCK_TAI			11
 
 #define MAX_CLOCKS			16
+
+/*
+ * AUX clock support. AUXiliary clocks are dynamically configured by
+ * enabling a clock ID. These clock can be steered independently of the
+ * core timekeeper. The kernel can support up to 8 auxiliary clocks, but
+ * the actual limit depends on eventual architecture constraints vs. VDSO.
+ */
+#define CLOCK_AUX			MAX_CLOCKS
+#define MAX_AUX_CLOCKS			8
+#define CLOCK_AUX_LAST			(CLOCK_AUX + MAX_AUX_CLOCKS - 1)
+
 #define CLOCKS_MASK			(CLOCK_REALTIME | CLOCK_MONOTONIC)
 #define CLOCKS_MONO			CLOCK_MONOTONIC