Merge branch 'gve-add-support-for-ptp-gettimex64'

Jordan Rhee says:

====================
gve: add support for PTP gettimex64

This patch series adds support to obtain near-simultaneous NIC and
system timestamps with gettimex64. This enables daemons like
chrony and phc2sys to synchronize the system clock to the NIC clock.

GVE does not have direct register access to the NIC hardware clock, so
it must issue an AdminQ command to read the NIC clock. Two paths
for obtaining a cross-timestamp are implemented: a precise path using
system counter values sampled by the device, and a fallback path using
system counter values sampled in the driver using
ptp_read_system_prets()/postts().

To use the precise path, the current system clocksource must match the
units returned by the device, which on x86 is X86_TSC and on ARM64 is
ARM_ARCH_COUNTER. The clockid requested for the cross-timestamp must
be either CLOCK_REALTIME or CLOCK_MONOTONIC_RAW. These conditions hold
by default on GCP VMs using Chrony, so we expect the precise path to be
used the vast majority of the time. If the system clocksource is changed
to kvm-clock, it activates the fallback path. Ethtool counters have been
added to count how many times each path is used.

The uncertainty window in the precise path is typically around 1-2us,
while in the fallback path is around 60-80us. This table shows a
comparison in chrony tracking statistics between the precise path and
fallback path. The RMS offset is nearly 4 orders of magnitude smaller
in the precise path.

|                 | Fallback Path         | Precise path             |
| --------------- | --------------------- | ------------------------ |
| System time     | 0.000000005 s slow    | 0.000000001 s fast       |
| Last offset     | +0.000005606 seconds  | +0.000000001 seconds     |
| RMS offset      | 0.000009020 seconds   | 0.000000002 seconds      |
| Frequency       | 4.115 ppm fast        | 0.362 ppm fast           |
| Residual freq   | +2.515 ppm            | +0.000 ppm               |
| Skew            | 18.480 ppm            | 0.001 ppm                |
| Root delay      | 0.000000001 seconds   | 0.000000001 seconds      |
| Root dispersion | 0.000081905 seconds   | 0.000001169 seconds      |
| Update interval | 0.5 seconds           | 0.5 seconds              |
| Leap status     | Normal                | Normal                   |

The first two patches pave the way for the PTP implementation by
quieting excessive logging and refactoring an existing routine for
thread safety.
====================

Link: https://patch.msgid.link/20260514225842.110706-1-hramamurthy@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>