/dev/ttyUSB3 connection problem

[will-caruana]

When running Kernel: Linux 5.4.51-v7l+ I am unable to connect to my cell modem on /dev/ttyUSB3

The temporary fix I am using is running:

sudo rpi-update a995f0c9a9b3e5dbd2a41f69f5c4c82cdf33c7ec

[rocketjosh]

Adding more to this issue:

The cell modem in question is the Quectel BG96, and it appears as though some changes in 5.4.66 have affected how USB3 is treated?

From this link:

Change rules for EC21, EC25, BG96 and EG95 to match vendor specific
serial functions only, to prevent binding to class functions. Require
2 endpoints on ff/ff/ff functions, avoiding the 3 endpoint QMI/RMNET
network functions.

As @will-caruana mentions, reverting to 5.4.65 allows for BG96 to load correctly.

[pelwell]

If you draw the traditional 4-box diagram (showing all combinations of two binary variables) with upstream/downstream on one axis and Raspberry Pi/third-party on the other, this issue falls squarely into the least supported quadrant - it's an upstream change causing a problem with a third-party product.

If you find an upstream fix for it, or even a fix written by somebody else, there's a chance we might accept it in our Linux repo (which is where the issue should have been reported) , but we're not going to investigate the problem.

[Ruffio]

@will-caruana is this issue still relevant? Else please close it, thanks :-)