igc: return early when failing to read EECD register

When booting with a dock connected, the igc driver may get stuck for ~40
seconds if PCIe link is lost during initialization.

This happens because the driver access device after EECD register reads
return all F's, indicating failed reads. Consequently, hw->hw_addr is set
to NULL, which impacts subsequent rd32() reads. This leads to the driver
hanging in igc_get_hw_semaphore_i225(), as the invalid hw->hw_addr
prevents retrieving the expected value.

To address this, a validation check and a corresponding return value
catch is added for the EECD register read result. If all F's are
returned, indicating PCIe link loss, the driver will return -ENXIO
immediately. This avoids the 40-second hang and significantly improves
boot time when using a dock with an igc NIC.

Log before the patch:
[    0.911913] igc 0000:70:00.0: enabling device (0000 -> 0002)
[    0.912386] igc 0000:70:00.0: PTM enabled, 4ns granularity
[    1.571098] igc 0000:70:00.0 (unnamed net_device) (uninitialized): PCIe link lost, device now detached
[   43.449095] igc_get_hw_semaphore_i225: igc 0000:70:00.0 (unnamed net_device) (uninitialized): Driver can't access device - SMBI bit is set.
[   43.449186] igc 0000:70:00.0: probe with driver igc failed with error -13
[   46.345701] igc 0000:70:00.0: enabling device (0000 -> 0002)
[   46.345777] igc 0000:70:00.0: PTM enabled, 4ns granularity

Log after the patch:
[    1.031000] igc 0000:70:00.0: enabling device (0000 -> 0002)
[    1.032097] igc 0000:70:00.0: PTM enabled, 4ns granularity
[    1.642291] igc 0000:70:00.0 (unnamed net_device) (uninitialized): PCIe link lost, device now detached
[    5.480490] igc 0000:70:00.0: enabling device (0000 -> 0002)
[    5.480516] igc 0000:70:00.0: PTM enabled, 4ns granularity

Fixes: ab40561 ("igc: Add NVM support")
Cc: Chia-Lin Kao (AceLan) <[email protected]>
Signed-off-by: En-Wei Wu <[email protected]>
Reviewed-by: Vitaly Lifshits <[email protected]>
Tested-by: Mor Bar-Gabay <[email protected]>
Signed-off-by: Tony Nguyen <[email protected]>

drivers/net/ethernet/intel/igc/igc_base.c

@@ -68,6 +68,10 @@ static s32 igc_init_nvm_params_base(struct igc_hw *hw)
 	u32 eecd = rd32(IGC_EECD);
 	u16 size;
 
+	/* failed to read reg and got all F's */
+	if (!(~eecd))
+		return -ENXIO;
+
 	size = FIELD_GET(IGC_EECD_SIZE_EX_MASK, eecd);
 
 	/* Added to a constant, "size" becomes the left-shift value
@@ -221,6 +225,8 @@ static s32 igc_get_invariants_base(struct igc_hw *hw)
 
 	/* NVM initialization */
 	ret_val = igc_init_nvm_params_base(hw);
+	if (ret_val)
+		goto out;
 	switch (hw->mac.type) {
 	case igc_i225:
 		ret_val = igc_init_nvm_params_i225(hw);