net: macb: avoid calling phylink_init_phydev fixed link devices

In case of fixed link devices the mdiodev in mdio_device_reset() is
null leading to the following crash:

8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 000001f0
[000001f0] *pgd=00000000
Internal error: Oops: 5 [#1] ARM
Modules linked in: tag_ksz ksz_spi ksz_switch dsa_core bridge stp llc microchip lan78xx atmel_usba_udc
CPU: 0 PID: 249 Comm: sh Not tainted 6.1.22-linux4microchip-2023.04-rc1+ torvalds#46
Hardware name: Atmel SAMA5
PC is at mdio_device_reset+0x8/0x9c
LR is at phy_init_hw+0x10/0xa4
pc : [<c058f1a8>]    lr : [<c058cbd0>]    psr: 600b0013
sp : e0b61d80  ip : 00000100  fp : c0ab43cc
r10: c0d92d50  r9 : 00000100  r8 : c13d1000
r7 : c13d0520  r6 : c13d1c0c  r5 : c13d0000  r4 : 00000000
r3 : c1ad4440  r2 : 00000000  r1 : 00000000  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c53c7d  Table: 21b20059  DAC: 00000051
Register r0 information: NULL pointer
Register r1 information: NULL pointer
Register r2 information: NULL pointer
Register r3 information: slab task_struct start c1ad4440 pointer offset 0
Register r4 information: NULL pointer
Register r5 information: slab kmalloc-cg-8k start c13d0000 pointer offset 0 size 8192
Register r6 information: slab kmalloc-cg-8k start c13d0000 pointer offset 7180 size 8192
Register r7 information: slab kmalloc-cg-8k start c13d0000 pointer offset 1312 size 8192
Register r8 information: slab kmalloc-cg-8k start c13d0000 pointer offset 4096 size 8192
Register r9 information: non-paged memory
Register r10 information: non-slab/vmalloc memory
Register r11 information: non-slab/vmalloc memory
Register r12 information: non-paged memory
Process sh (pid: 249, stack limit = 0x74d3815e)
Stack: (0xe0b61d80 to 0xe0b62000)
1d80: 00000000 c13d0000 c13d1c0c c058cbd0 c13d1b64 c059d098 e0b61d9 00000006
1da0: e0b61dc0 c04fdbc0 c1056c10 c04fdbc0 c1056c10 c0d71eec 00000010 b66d215e
1dc0: 00000006 c0509e84 c1056c10 c0d5300c c1056c50 00000001 c1056c10 00000000
1de0: 00000010 c1056c54 00000010 c050a8b4 c1056c8c c0d52fe8 c1056c10 c0d52fe8
1e00: c0d5300c c050b4d8 00000010 c050b33c 931f958c 00000006 8eff9f7e 00000006
1e20: c0aeb4cc 00000010 00000001 00000002 00000000 c0d032b8 c0d0c6a4 00000000
1e40: c0d71ef c050b7d0 c0d71f0 c01483c0 c0aab0c4 c1ad4440 c0d03240 c0d032b0
1e60: 0056c190 c014bf68 e0b61e8c 29aa0439 c1ad4440 00000000 00000002 c0d032b0
1e80: c0aab0c4 00000008 c1bae640 c28c5110 0056c190 c0148928 00000002 c0adae58
1ea0: 00000007 c0d71f18 00000008 c0147378 00000008 c28c5100 00000000 00000000
1ec0: c1bae640 e0b61f28 c28c5110 c0262340 00000000 00000000 c1c0a600 c1ad4440
1ee0: 0056ebc8 00000008 c0908ac8 00004004 00000000 c01ee76 c290ea80 c1ad4440
1f00: c290ea80 0000000a 0000000a e0b61f78 01010006 00000008 00000000 0056ebc8
1f20: 00000000 00000000 c1c0a600 00000000 00000000 00000000 00000000 00000000
1f40: 00000000 00004004 00000000 00000000 00000001 29aa0439 c1c0a600 c1c0a600
1f60: 00000000 00000000 c1ad4440 0056ebc8 00000008 c01ee998 00000000 00000000
1f80: 00000000 29aa0439 00000001 00000000 b6f54480 00000004 c01002c0 c1ad4440
1fa0: 00000004 c0100060 00000001 00000000 00000001 0056ebc8 00000008 00000000
1fc0: 00000001 00000000 b6f54480 00000004 00000008 bed176c0 00000020 0056c190
1fe0: 00000004 bed17670 b6e675c7 b6dea9b6 60000030 00000001 00000000 00000000
 mdio_device_reset from phy_init_hw+0x10/0xa4
 phy_init_hw from macb_resume+0x2ac/0x358
 macb_resume from dpm_run_callback.constprop.8+0x3c/0xbc
 dpm_run_callback.constprop.8 from device_resume+0xa4/0x17c
 device_resume from dpm_resume+0xd0/0x200
 dpm_resume from dpm_resume_end+0xc/0x18
 dpm_resume_end from suspend_devices_and_enter+0x2a4/0x5e4
 suspend_devices_and_enter from pm_suspend+0x228/0x338
 pm_suspend from state_store+0x6c/0xc8
 state_store from kernfs_fop_write_iter+0x118/0x1b4
 kernfs_fop_write_iter from vfs_write+0x294/0x34c
 vfs_write from ksys_write+0xa0/0xd0
 ksys_write from ret_fast_syscall+0x0/0x54
Exception stack(0xe0b61fa8 to 0xe0b61ff0)
1fa0:                   00000001 00000000 00000001 0056ebc8 00000008 00000000
1fc0: 00000001 00000000 b6f54480 00000004 00000008 bed176c0 00000020 0056c190
1fe0: 00000004 bed17670 b6e675c7 b6dea9b6
Code: e8bd4010 eafffc67 e92d4070 e1a04000 (e59001f0)
---[ end trace 0000000000000000 ]---

Fixes: e0bc931 ("net: macb: fix ethernet after resume")
Fixes: 15a9dbe ("net: macb: Specify PHY PM management done by MAC")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>

drivers/net/ethernet/cadence/macb_main.c

@@ -5227,7 +5227,8 @@ static int __maybe_unused macb_resume(struct device *dev)
 	if (!device_may_wakeup(&bp->dev->dev))
 		phy_init(bp->sgmii_phy);
 
-	phylink_init_phydev(bp->phylink);
+	if (!of_phy_is_fixed_link(bp->pdev->dev.of_node))
+		phylink_init_phydev(bp->phylink);
 	phylink_start(bp->phylink);
 	rtnl_unlock();