diff options
| author | David Woodhouse <dwmw@amazon.co.uk> | 2026-06-04 10:35:18 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@kernel.org> | 2026-06-05 14:25:03 +0200 |
| commit | bc484a5096732cd858771cccd3164ec985bdc03d (patch) | |
| tree | cdb7872103b2dd686abc8548ca6fc63913f19fee | |
| parent | 19fa3e50644d2d47fca713b0df640f67dcd26634 (diff) | |
ptp: vmclock: Use hw_cycles from snapshot for precise TSC pairingrefs/merge-window/df7610115bad68761e38a34648dfd6f5cd161cd6
When the system clocksource is kvmclock or Hyper-V (not the TSC directly),
vmclock_get_crosststamp() falls through to a separate get_cycles() call,
losing the atomic pairing between the system time snapshot and the TSC
reading.
Now that ktime_get_snapshot_id() populates hw_cycles with the underlying
TSC value for derived clocksources, use it when available. This gives a
perfect (system_time, tsc) pairing for the device time calculation.
The SUPPORT_KVMCLOCK wrapper is still needed to convert the TSC into
kvmclock nanoseconds for system_counter->cycles, because otherwise
get_device_system_crosststamp() can't interpret the result against the
system clock.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Assisted-by: Kiro:claude-opus-4.6-1m
Link: https://patch.msgid.link/20260604095755.64849-4-dwmw2@infradead.org
| -rw-r--r-- | drivers/ptp/ptp_vmclock.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/drivers/ptp/ptp_vmclock.c b/drivers/ptp/ptp_vmclock.c index d6a5a533164a..eebdcd5ebc08 100644 --- a/drivers/ptp/ptp_vmclock.c +++ b/drivers/ptp/ptp_vmclock.c @@ -140,6 +140,10 @@ static int vmclock_get_crosststamp(struct vmclock_state *st, if (sts->pre_sts.cs_id == st->cs_id) { cycle = sts->pre_sts.cycles; sts->post_sts = sts->pre_sts; + } else if (sts->pre_sts.hw_csid == st->cs_id && + sts->pre_sts.hw_cycles) { + cycle = sts->pre_sts.hw_cycles; + sts->post_sts = sts->pre_sts; } else { cycle = get_cycles(); ptp_read_system_postts(sts); |