net: macb: Fix wake device without assigned IP address

Fix kernel crash when system is suspended with GEM as wake device and
there's no IP address assigned to the GEM interface.
When system is suspended with GEM as wake device and there's no
IP address assigned to it, kernel crashes with a null pointer exception
as shown below. This patch adds a null pointer check and returns error
when there's no IP address assigned.

Error log:
 Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030
 Mem abort info:
   ESR = 0x96000004
   EC = 0x25: DABT (current EL), IL = 32 bits
   SET = 0, FnV = 0
   EA = 0, S1PTW = 0
 Data abort info:
   ISV = 0, ISS = 0x00000004
   CM = 0, WnR = 0
 user pgtable: 4k pages, 48-bit VAs, pgdp=00000008081d4000
 [0000000000000030] pgd=0000000000000000, p4d=0000000000000000
 Internal error: Oops: 96000004 [#1] SMP
 Modules linked in: zocl(O) [last unloaded: zocl]
 CPU: 1 PID: 769 Comm: sh Tainted: G           O      5.10.0-xilinx-v2020.2 #1
 Hardware name: ZynqMP ZCU102 Rev1.0 (DT)
 pstate: 60000085 (nZCv daIf -PAN -UAO -TCO BTYPE=--)
 pc : macb_suspend+0x1d4/0x344
 lr : macb_suspend+0x1b0/0x344
 sp : ffff8000119b3b20
 x29: ffff8000119b3b20 x28: ffff000800872500
 x27: 0000000000000002 x26: ffff00080622db00
 x25: 0000000000000000 x24: ffff000800384010
 x23: 00000000000008f8 x22: ffff00080622c000
 x21: 0000000000000002 x20: ffff00080622cad0
 x19: ffff00080622c840 x18: 0000000000000030
 x17: 000000000000000b x16: 000000000000000b
 x15: ffff000800872918 x14: ffffffffffffffff
 x13: ffff8000113b3de0 x12: 0000000000000540
 x11: 00000000000001c0 x10: ffff8000113dfde0
 x9 : 00000000fffff800 x8 : ffff8000113b3de0
 x7 : 0000000000000000 x6 : 0000000000000000
 x5 : 0000000000000130 x4 : ffff800010822290
 x3 : ffff800010822290 x2 : 0000000000000000
 x1 : 00000000000000b8 x0 : ffff00080622c840
 Call trace:
  macb_suspend+0x1d4/0x344
  __device_suspend+0x100/0x41c
  dpm_suspend+0x108/0x1cc
  dpm_suspend_start+0x7c/0xa0
  suspend_devices_and_enter+0x138/0x55c
  pm_suspend+0x1e4/0x290
  state_store+0x8c/0x110
  kobj_attr_store+0x1c/0x30
  sysfs_kf_write+0x48/0x60
  kernfs_fop_write+0xfc/0x21c
  vfs_write+0xf0/0x2b0
  ksys_write+0x6c/0x100
  __arm64_sys_write+0x20/0x30
  el0_svc_common.constprop.0+0x94/0x1c0
  do_el0_svc+0x44/0xb0
  el0_svc+0x14/0x20
  el0_sync_handler+0x1a4/0x1b0
  el0_sync+0x174/0x180
 Code: f9400e63 52801701 f9415c42 f9400842 (b9403042)
 ---[ end trace 0be3f330841cc22a ]---

Signed-off-by: Pranavi Somisetty <pranavi.somisetty@xilinx.com>
Acked-by: Harini Katakam <harini.katakam@xilinx.com>
State: pending

drivers/net/ethernet/cadence/macb_main.c

@@ -4714,6 +4714,10 @@ static int __maybe_unused macb_suspend(struct device *dev)
 		return 0;
 
 	if (device_may_wakeup(&bp->dev->dev)) {
+		if (!bp->dev->ip_ptr->ifa_list) {
+			netdev_err(netdev, "IP address not assigned\n");
+			return -EOPNOTSUPP;
+		}
 		spin_lock_irqsave(&bp->lock, flags);
 		ctrl = macb_readl(bp, NCR);
 		ctrl &= ~(MACB_BIT(TE) | MACB_BIT(RE));