Some PTP hardware clock (PHC) devices may return -EOPNOTSUPP for
operations like settime, adjtime, or adjfreq. This commonly occurs
with timestamp-only PHC implementations that don't support full clock
control.

For background, syzbot previously exposed a crash risk when PTP clock
drivers lacked required callbacks[1]. Subsequent work[2] made callback
presence a registration requirement. As a result, some drivers (like
iwlwifi MVM/MLD[3]) now provide stub callbacks that return -EOPNOTSUPP
for unsupported operations.

When phc_ctl encounters such devices, the "Operation not supported"
error should be treated as a skip (device limitation) rather than a
test failure. This patch:
- Adds [SKIP] output handling in log_test()
- Detects "Operation not supported" from phc_ctl and returns ksft_skip
- Returns ksft_skip if all tests are skipped, preventing false-positive
  results when testing timestamp-only PHC implementations

Link: https://lore.kernel.org/netdev/20251028043216.1971292-1-junjie.cao@intel.com/ [1]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=dfb073d32cac [2]
Link: https://lore.kernel.org/netdev/20251204123204.9316-1-ziyao@disroot.org/ [3]
Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260126061532.12532-2-junjie.cao@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The kselftest framework defines KSFT_SKIP=4 as the standard exit code
for skipped tests. However, phc.sh currently uses a mix of 'exit 0' and
'exit 1' to indicate skip conditions, which can confuse test harnesses
and CI systems.

This patch introduces ksft_skip=4 variable and unifies all skip exit
paths to use 'exit $ksft_skip', consistent with other selftests like
net/lib.sh and net/fib_nexthops.sh.

Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260126061532.12532-1-junjie.cao@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Test the PTP Physical Hardware Clock functionality using the "phc_ctl" (a
part of "linuxptp").

The test contains three sub-tests:
  * "settime" test
  * "adjtime" test
  * "adjfreq" test

"settime" test:
  * set the PHC time to 0 seconds.
  * wait for 120.5 seconds.
  * check if PHC time equal to 120.XX seconds.

"adjtime" test:
  * set the PHC time to 0 seconds.
  * adjust the time by 10 seconds.
  * check if PHC time equal to 10.XX seconds.

"adjfreq" test:
  * adjust the PHC frequency to be 1% faster.
  * set the PHC time to 0 seconds.
  * wait for 100.5 seconds.
  * check if PHC time equal to 101.XX seconds.

Usage:
  $ ./phc.sh /dev/ptp<X>

  It is possible to run a subset of the tests, for example:
    * To run only the "settime" test:
      $ TESTS="settime" ./phc.sh /dev/ptp<X>

Signed-off-by: Shalom Toledo <shalomt@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Tested-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>