mt7621 - Help debugging a sporadic PCI issue

[Caleb James DeLisle]

Hello folks,

Last Sunday I opened https://github.com/openwrt/openwrt/issues/12359 which is a sporadic PCI issue 
manifesting in one of the 2 wifi cards not coming online roughly 50% of all reboots.

The problem coincides with bridge 0000:00:01.0 not having any flags on its PCI_COMMAND register.

I added some debug lines to print PCI_COMMAND at various times during boot so that I could see where 
the flags are lost, and I narrowed it down to a place where, bizarrely, there is no code of any 
significance.

Although I am working on 22.03, I also reproduced this issue with the current master branch as of 
this week, so I believe it is not fixed. I also think this is likely to be the same issue causing 
https://github.com/openwrt/mt76/issues/644

If somebody could give me some direction re debugging this further, I would be most grateful.

Thanks,
Caleb