junk character issue on minicom and screen

[Johan Hovold]

On Mon, Jun 24, 2019 at 02:57:34PM +0530, Shyam Saini wrote:
> Hello everyone,
> 
> I'm working on Rockchip rk3399 Nanopc t4 board and I'm trying get
> serial output from board using minicom and my board has baudrate
> 1500000.
> 
> I'm using a usb to serial converter. So, when i power on my board
> minicom starts to give junk characters.
> Minicom version:  2.7.1
> USB driver probed : cp210x
> 
> But when I use the same setup with my colleagues laptop it gives
> correct output (kernel version 4.15.0-52-generic ).
> 
> Note that my colleague and i used same setup
> Same usb driver probed
> Same power adapter
> same usb to serial converter wire
> same minicom version.
> same baudrate
> 
> Other thing which i tried is switching kernel version and it turns out
> that one of the older distro kernel on my system (debian 4.9.0-5-amd64
> ) is working fine and it seems like there is something changed in
> newer kernel vesions.
> Here is the quick summary
> 4.19.0-4-amd64    -> not working
> 4.15.0-52-generic -> working
> 4.9.0-5-amd64      -> working
> 5.2.0-rc4+             -> not working

Thanks for the report. There were some changes between 4.15 and 4.19
related to the line speed handling which may have broken something in
your setup.

Do you know which variant of cp210x you have? Can your provide the
output of lsusb -v?

Also if you can run driver with debugging enabled when connecting the
device and setting the line speed, that may give a clue about what is
going on. For example,

	echo module cp210x =p > /sys/kernel/debug/dynamic_debug/control

Does 115200 bps still work by the way?

Johan