[FS#687] Meraki MR24: Ethernet interface not detected correctly if cable not plugged at boot time

[LEDE Bugs]

The following task has a new comment added:

FS#687 - Meraki MR24: Ethernet interface not detected correctly if cable not plugged at boot time
User who did this - Christian Lamparter (chunkeey)

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Hello,

I don't have a MR24 myself. But I know that the MyBook Live. (Same single RGMII PHY setup, but with a Broadcom PHY BCM54610) doesn't have a problem with detecting the PHY during startup, even if no ethernet cable is connected to it. I've tested todays image from downloads.lede-project.org: r3925-64175ff

Since I think this is something specific to the MR24 and since you said "but it’s been a problem since at least last September.". I think it must have been a issue from the beginning. Is this correct? Or do you remember an older version, were this was working as intended?

As for debugging this. Is this phy detection error just a problem during boot-time? Or does it persist? I think you could test this by unbinding and rebinding the emac driver as root when the MR24 has finished booting and is running: 



# echo "4ef600c00.ethernet" > /sys/bus/platform/drivers/emac/unbind

# echo "4ef600c00.ethernet" > /sys/bus/platform/drivers/emac/bind

[  208.654537] /plb/opb/emac-rgmii at ef601500: input 0 in RGMII mode
[  208.661902] eth0: EMAC-0 /plb/opb/ethernet at ef600c00, MAC 00:90:aa:31:32:25
[  208.668772] eth0: found Generic MII PHY (0x01) 
(The MBL can use the generic PHY driver)
...


If the PHY is still not detected, then it has to be something else.

(maybe the bootloader disables the PHY via GPIO? Does Cisco advertise such a feature? In that case a dump of /sys/kernel/debug/gpio with and w/o ethernet cable attached during boot might help). 
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=687#comment2348