ptp: allow reading of currently dialed frequency to succeed on free-running clocks

JIRA: https://issues.redhat.com/browse/RHEL-115596

commit aa112cb
Author: Vladimir Oltean <vladimir.oltean@nxp.com>
Date:   Fri Jun 13 20:47:49 2025 +0300

    ptp: allow reading of currently dialed frequency to succeed on free-running clocks

    There is a bug in ptp_clock_adjtime() which makes it refuse the
    operation even if we just want to read the current clock dialed
    frequency, not modify anything (tx->modes == 0). That should be possible
    even if the clock is free-running. For context, the kernel UAPI is the
    same for getting and setting the frequency of a POSIX clock.

    For example, ptp4l errors out at clock_create() -> clockadj_get_freq()
    -> clock_adjtime() time, when it should logically only have failed on
    actual adjustments to the clock, aka if the clock was configured as
    slave. But in master mode it should work.

    This was discovered when examining the issue described in the previous
    commit, where ptp_clock_freerun() returned true despite n_vclocks being
    zero.

    Fixes: 73f3706 ("ptp: support ptp physical/virtual clocks conversion")
    Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
    Link: https://patch.msgid.link/20250613174749.406826-3-vladimir.oltean@nxp.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

drivers/ptp/ptp_clock.c

@@ -121,7 +121,8 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct __kernel_timex *tx)
 	struct ptp_clock_info *ops;
 	int err = -EOPNOTSUPP;
 
-	if (ptp_clock_freerun(ptp)) {
+	if (tx->modes & (ADJ_SETOFFSET | ADJ_FREQUENCY | ADJ_OFFSET) &&
+	    ptp_clock_freerun(ptp)) {
 		pr_err("ptp: physical clock is free running\n");
 		return -EBUSY;
 	}