[PATCH v7 net-next 3/3] selftests: drivers/net: Implement ptp4l sync test using netdevsim

[Maciek Machnikowski <maciek@machnikowski.net>]

Add PTP synchronization test using ptp4l and netdevsim.
The test uses the NetDrvEpEnv to link a local netdevsim
device to a remote endpoint, runs ptp4l as leader and follower
on the two ends, and waits for the follower to report the
synchronized state (s2).

Signed-off-by: Maciek Machnikowski <maciek@machnikowski.net>
---
 tools/testing/selftests/drivers/net/Makefile |  1 +
 tools/testing/selftests/drivers/net/config   |  1 +
 tools/testing/selftests/drivers/net/ptp.py   | 82 ++++++++++++++++++++
 3 files changed, 84 insertions(+)
 create mode 100755 tools/testing/selftests/drivers/net/ptp.py

diff --git a/tools/testing/selftests/drivers/net/Makefile b/tools/testing/selftests/drivers/net/Makefile
index d5bf4cb638a8..18bb7c693b69 100644
--- a/tools/testing/selftests/drivers/net/Makefile
+++ b/tools/testing/selftests/drivers/net/Makefile
@@ -19,6 +19,7 @@ TEST_PROGS := \
 	netpoll_basic.py \
 	ping.py \
 	psp.py \
+	ptp.py \
 	queues.py \
 	ring_reconfig.py \
 	shaper.py \
diff --git a/tools/testing/selftests/drivers/net/config b/tools/testing/selftests/drivers/net/config
index 91d4fd410914..df28da831a7b 100644
--- a/tools/testing/selftests/drivers/net/config
+++ b/tools/testing/selftests/drivers/net/config
@@ -13,5 +13,6 @@ CONFIG_NET_SCH_ETF=m
 CONFIG_NET_SCH_FQ=m
 CONFIG_PPP=y
 CONFIG_PPPOE=y
+CONFIG_PTP_1588_CLOCK_MOCK=y
 CONFIG_VLAN_8021Q=m
 CONFIG_XDP_SOCKETS=y
diff --git a/tools/testing/selftests/drivers/net/ptp.py b/tools/testing/selftests/drivers/net/ptp.py
new file mode 100755
index 000000000000..92a943dcbb06
--- /dev/null
+++ b/tools/testing/selftests/drivers/net/ptp.py
@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# By Maciek Machnikowski <maciek@machnikowski.net> (c) 2026,
+
+"""
+Test suite for PTP sync using ptp4l.
+
+Start a ptp4l leader and follower and check that the follower locks onto the
+leader (state s2)
+"""
+
+import time
+
+from lib.py import (
+    NetDrvEpEnv,
+    bkg,
+    fd_read_timeout,
+    ksft_exit,
+    ksft_pr,
+    ksft_run,
+    ksft_true,
+)
+
+PTP4L_SYNC_TIMEOUT = 40
+
+
+def _poll_follower_sync(follower, timeout):
+    """Read the follower stdout pipe until ptp4l reports sync state s2.
+
+    Returns a tuple (synced, output) where output is the text read so far.
+    """
+    fd_file = follower.proc.stdout
+    fd = fd_file.fileno()
+    buf = b""
+    deadline = time.monotonic() + timeout
+    while time.monotonic() < deadline:
+        if b" s2 " in buf:
+            break
+        if follower.proc.poll() is not None:
+            chunk = fd_file.read()
+            if chunk:
+                buf += chunk
+            break
+        try:
+            remaining = deadline - time.monotonic()
+            buf += fd_read_timeout(fd, min(1, remaining))
+        except TimeoutError:
+            continue
+    return b" s2 " in buf, buf.decode("utf-8", "replace")
+
+
+def ptp_sync_test(cfg):
+    """Verify ptp4l leader/follower synchronization reaches state s2."""
+    cfg.require_cmd("ptp4l", remote=True)
+
+    leader_cmd = f"ptp4l -i {cfg.remote_ifname} -m -2"
+    follower_cmd = f"ptp4l -i {cfg.ifname} -m -s -2"
+
+    with bkg(leader_cmd, host=cfg.remote), \
+         bkg(follower_cmd) as follower:
+        synced, output = _poll_follower_sync(follower, PTP4L_SYNC_TIMEOUT)
+
+    if synced:
+        return
+
+    ksft_pr(f"ptp4l follower did not reach locked state (s2) within "
+            f"{PTP4L_SYNC_TIMEOUT}s")
+    tail = output.strip().split("\n")[-10:]
+    ksft_pr("Follower log (last 10 lines): " + " | ".join(tail))
+    ksft_true(False, "PTP sync timeout")
+
+
+def main():
+    """Run ksft tests."""
+    with NetDrvEpEnv(__file__) as cfg:
+        ksft_run([ptp_sync_test], args=(cfg, ))
+    ksft_exit()
+
+
+if __name__ == "__main__":
+    main()
-- 
2.55.0