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ptp: ptp_vmclock: return TAI not UTC

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To output UTC would involve complex calculations about whether the time
elapsed since the reference time has crossed the end of the month when
a leap second takes effect. I've prototyped that, but it made me sad.

Much better to report TAI, which is what PHCs should do anyway.
And much much simpler.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Babis Chalios <bchalios@amazon.es>
Tested-by: Takahiro Itazuri <itazur@amazon.com>
Link: https://patch.msgid.link/20260130173704.12575-8-itazur@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
David Woodhouse 2026-01-30 17:36:06 +00:00 • committed by Jakub Kicinski
parent ac1e740492
commit 562f59fe32
1 changed files with 5 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

10
drivers/ptp/ptp_vmclock.c
View file

@ -83,13 +83,13 @@ static uint64_t mul_u64_u64_shr_add_u64(uint64_t *res_hi, uint64_t delta,
static bool tai_adjust(struct vmclock_abi *clk, uint64_t *sec)
{
if (likely(clk->time_type == VMCLOCK_TIME_UTC))
if (clk->time_type == VMCLOCK_TIME_TAI)
return true;
if (clk->time_type == VMCLOCK_TIME_TAI &&
if (clk->time_type == VMCLOCK_TIME_UTC &&
(le64_to_cpu(clk->flags) & VMCLOCK_FLAG_TAI_OFFSET_VALID)) {
if (sec)
*sec += (int16_t)le16_to_cpu(clk->tai_offset_sec);
*sec -= (int16_t)le16_to_cpu(clk->tai_offset_sec);
return true;
}
return false;
@ -350,9 +350,9 @@ static struct ptp_clock *vmclock_ptp_register(struct device *dev,
return NULL;
}
/* Only UTC, or TAI with offset */
/* Accept TAI directly, or UTC with valid offset for conversion to TAI */
if (!tai_adjust(st->clk, NULL)) {
dev_info(dev, "vmclock does not provide unambiguous UTC\n");
dev_info(dev, "vmclock does not provide unambiguous time\n");
return NULL;
}