USB problems on FreeBSD-current and Raspberry Pi3B+, MMCCAM perhaps?

[bob prohaska]

A UGreen USB3 storage card adapter (model 30333) has stopped working
with FreeBSD-current, reporting a stream of 

(da1:umass-sim1:1:0:0): TEST UNIT READY. CDB: 00 00 00 00 00 00 
(da1:umass-sim1:1:0:0): CAM status: SCSI Status Error
(da1:umass-sim1:1:0:0): SCSI status: Check Condition
(da1:umass-sim1:1:0:0): SCSI sense: NOT READY asc:3a,0 (Medium not present)
(da1:umass-sim1:1:0:0): Error 6, Unretryable error
(da2:umass-sim1:1:0:1): TEST UNIT READY. CDB: 00 00 00 00 00 00 
(da2:umass-sim1:1:0:1): CAM status: SCSI Status Error
(da2:umass-sim1:1:0:1): SCSI status: Check Condition
(da2:umass-sim1:1:0:1): SCSI sense: NOT READY asc:3a,0 (Medium not present)
(da2:umass-sim1:1:0:1): Error 6, Unretryable error
in what looks like an infinite loop (there are 4 daX devices on the adapter).

The present kernel displaying these errors is 
FreeBSD 13.0-CURRENT (GENERIC-MMCCAM) #5 main-c255664-g4d64c7243d26: 
Sat Jan  9 11:27:58 PST 2021

Unplugging the adapter restores normal operation.

Rebooting to 
FreeBSD www.zefox.org 13.0-CURRENT FreeBSD 13.0-CURRENT #3 r361820: Sun Jun  7 22:19:00 PDT 2020     bob at www.zefox.org:/usr/obj/usr/src/arm64.aarch64/sys/GENERIC  arm64
exhibits normal behavior, the adapter can be read and written without trouble.

As an aside, a Raspberry Pi4 8GB suffers even worse mischief when the adapter
is connected, losing communication with the USB root device even after the
adapter is unplugged.  A power cycle is required to recover. That system is
Linux raspberrypi 5.4.83-v7l+ #1379 SMP Mon Dec 14 13:11:54 GMT 2020 armv7l GNU/Linux
Since it implements onboard WiFi presumably it has some equivalent to MMCCAM.

Might this behavior have anything to do with MMCCAM ? 

Thanks for reading,

bob prohaska