Strange Serial/Modem Behavior on Slackware64 Current

I was trying to get a HylaFax+ 7.0.2 install going on Slackware64 Current with a pair of MultiTech MT5634ZPX-PCI-U 1.32o modems. The modems seemed to never respond after editing the inittab and setting up faxgetty. So I decided to comment them out from the inittab and test them with minicom.

I can not execute AT commands within minicom in an expected manner. I do not get any response from the modem until I exit and restart minicom.

For example say I type an INIT string or just a series of ATZ commands followed by the enter key. Nothing ever appears on screen. If I do a control-a then x and exit and then restart minicom, the commands are then executed. I can do a control-a then M followed by ATI3 and then enter and I will get no output. Upon exiting and restarting minicom I get:
Welcome to minicom 2.7.1

OPTIONS: I18n
Compiled on Apr 13 2018, 08:09:10.
Port /dev/ttyS1, 19:35:30

Press CTRL-A Z for help on special keys

0
OK
AT S7=45 S0=0 L1 V1 X4 &c1 E1 Q0
OK
ATI3
LT V.92 1.0 MT5634ZPX-PCI-U Internal Data/Fax/Voice Modem Version 1.32o

OK
ATZ
OK

Any ideas?

Regards,
Adan Calderón

In case anyone out there is curious, I found out that live distro "Parted Magic" from May 2020, did not have the issue with my modems (MT5634ZPX-PCI). So I grab /proc/config.gz from that version of parted magic and used it to compile kernel 5.6.12 on Slackware64 Current. I am no longer seeing the issues I was before with kernels 5.4.xx. I would best describe them as maybe IRQ problems, but I am not sure. I would like to find out what changed in kernel 5.4.xx that caused the modems to stop responding instantly. I know older versions of slackware64 did not have this issue. I hope this info trickles down to the correct person. Thanks for reading.

All the best,
Adan Calderón

Originally Posted by AceStrider1 I hope this info trickles down to the correct person.

My appreciation for the investigation and happy to hear you sorted it out. Your issue is particular and it's hard to help if not owning the HW, I believe that's why you haven't got any replies.
Personally, I read your first post and noticed that you were actually able to communicate with the modem and started to consider that you might have some other issues there, like modem mode settings, serial settings, etc. Not owning and not knowing anything about your particular modem, I didn't have anything constructive to add.

The "correct person" for kernel related issues would be someone from the kernel devs team, if it's a kernel regression.

If you are able to identify the kernel options that resolved your problem, by comparing the kernel config file you obtained from "Parted Magic" with the one from the kernel provided by Slackware -current, then the Slackware team could also help by adding/disabling those options for the next kernel release, if those are not conflicting with the normal/general use.
Here you can get the actual Slackware -current kernel configs:
https://mirrors.slackware.com/slackw...ernel-configs/