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[ Upstream commited1fe1bebe] There are multi-generational drivers like mv88e6xxx which have code like this: int mv88e6xxx_port_hwtstamp_get(struct dsa_switch *ds, int port, struct ifreq *ifr) { if (!chip->info->ptp_support) return -EOPNOTSUPP; ... } DSA wants to deny PTP timestamping on the master if the switch supports timestamping too. However it currently relies on the presence of the port_hwtstamp_get() callback to determine PTP capability, and this clearly does not work in that case (method is present but returns -EOPNOTSUPP). We should not deny PTP on the DSA master for those switches which truly do not support hardware timestamping. Create a dsa_port_supports_hwtstamp() method which actually probes for support by calling port_hwtstamp_get() and seeing whether that returned -EOPNOTSUPP or not. Fixes:f685e609a3("net: dsa: Deny PTP on master if switch supports it") Link: https://patchwork.kernel.org/project/netdevbpf/patch/20221110124345.3901389-1-festevam@gmail.com/ Reported-by: Fabio Estevam <festevam@gmail.com> Reported-by: Steffen Bätz <steffen@innosonix.de> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Tested-by: Fabio Estevam <festevam@denx.de> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Sasha Levin <sashal@kernel.org>