net: fec: don't save PTP state if PTP is unsupported

Some platforms (such as i.MX25 and i.MX27) do not support PTP, so on
these platforms fec_ptp_init() is not called and the related members
in fep are not initialized. However, fec_ptp_save_state() is called
unconditionally, which causes the kernel to panic. Therefore, add a
condition so that fec_ptp_save_state() is not called if PTP is not
supported.

Fixes: a1477dc8 ("net: fec: Restart PPS after link state change")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/lkml/353e41fe-6bb4-4ee9-9980-2da2a9c1c508@roeck-us.net/Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Csókás, Bence <csokas.bence@prolan.hu>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://patch.msgid.link/20241008061153.1977930-1-wei.fang@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/fec_main.c

@@ -1077,7 +1077,8 @@ fec_restart(struct net_device *ndev)
 	u32 rcntl = OPT_FRAME_SIZE | 0x04;
 	u32 ecntl = FEC_ECR_ETHEREN;
 
-	fec_ptp_save_state(fep);
+	if (fep->bufdesc_ex)
+		fec_ptp_save_state(fep);
 
 	/* Whack a reset.  We should wait for this.
 	 * For i.MX6SX SOC, enet use AXI bus, we use disable MAC
@@ -1340,7 +1341,8 @@ fec_stop(struct net_device *ndev)
 			netdev_err(ndev, "Graceful transmit stop did not complete!\n");
 	}
 
-	fec_ptp_save_state(fep);
+	if (fep->bufdesc_ex)
+		fec_ptp_save_state(fep);
 
 	/* Whack a reset.  We should wait for this.
 	 * For i.MX6SX SOC, enet use AXI bus, we use disable MAC