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