timekeeping: Document monotonic raw timestamps in snapshots correctly

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The comments related to raw monotonic timestamps for the various
snapshot mechanisms in code and struct documentation are ambiguous. They
reference them as CLOCK_MONOTONIC_RAW timestamps, but with the arrival
of AUX clocks that's not longer correct.

The raw monotonic timestamps only represent CLOCK_MONOTONIC_RAW for the
system time clock IDs, i.e. REALTIME, MONOTONIC, BOOTTIME, TAI.

For AUX clocks they refer to the monotonic raw clock which is related to
the individual AUX clocks. These monotonic raw timestamps have the same
conversion factor as CLOCK_MONOTONIC_RAW, but differ from that by an
offset:

	MONORAW(AUX$N) = MONORAW(SYSTEM) + OFFSET(AUX$N)

The offset is established when a AUX clock is enabled and stays constant
for the lifetime of the AUX clock.

Update the comments so they reflect reality.

Reported-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/87wlv9k3wz.ffs@fw13

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This commit is contained in:

Thomas Gleixner 2026-07-05 14:38:04 +02:00

parent a73d7f98e4

commit e2904ddb14

2 changed files with 24 additions and 2 deletions

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10

include/linux/timekeeping.h

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16

kernel/time/timekeeping.c

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