re: port-arm/55922: Kernel panics with nvme+gpt on Pinebook Pro

[matthew green <mrg%eterna.com.au@localhost>]

what's the nvme ssd installed?  there are known issues with
many mid-range to high-end ssds in pbp, due to power supply
issues.  see this for info about known good bad:

   https://wiki.pine64.org/wiki/Pinebook_Pro_Hardware_Accessory_Compatibility#NVMe_SSD_drives

but also know that all the samsung drives *i* tried did not
work in the end (this table lists 970 PRO as working, and
maybe it does work at PS2 setting.)

you can (should) set the nvme power level to PS2 if you can,
using nvmectl:

   nvmectl power -p 2 nvme0


now that i've become more familiar with this failure mode,
i'm some what convinced this PR is a hardware issue and
we can't solve it in software.  the mutex spinout happened
because the hardware stopped answering.


it's also possible that even with nvme set to ~2W that
also having the system run -j6 for a long time -- which
does drain the battery normally -- will lead to a case
where the battery can't supply power to the nvme and it
can fail, even with "good low power" nvmes.  i have intel
660p's in use, and while mostly it can run down on power
OK, sometimes it will hang IOs and need a reset.


.mrg.