Comment 0 for bug 1919051

This device works flawlessly on Windows XP with native driver, both as a physical machine or inside a VM. It shows on XP's device management with a "USB 2.0" name.

On Ubuntu, Shorting pins 2 and 3 of DB9 connector does not give back characters sent (no echo), nor typed strings are sent to other RS232 devices, despite of communication settings. Characters from remote devices are correctly received. Using a null modem cable to other RS232 terminal shows that the local terminal receives, but does not transmit.

Its worth to mention: passing through the device to a guest virtual machine (KVM) running Windows XP makes it work correctly with XP driver inside the guest OS. Bringing back the device stops transmitting. Only receive works.

Tested with the version below:
NAME="Ubuntu"
VERSION="20.04.2 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.2 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

Kernel:
Linux host 5.4.0-66-generic #74-Ubuntu SMP Wed Jan 27 22:54:38 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

Device ID:
ID 4348:5523 WinChipHead USB->RS 232 adapter with Prolifec PL 2303 chipset

Modinfo:
filename: /lib/modules/5.4.0-66-generic/kernel/drivers/usb/serial/ch341.ko
license: GPL v2
srcversion: 8F5F64E72BDA4E76E6F4F4D
alias: usb:v4348p5523d*dc*dsc*dp*ic*isc*ip*in*
alias: usb:v1A86p7523d*dc*dsc*dp*ic*isc*ip*in*
alias: usb:v1A86p7522d*dc*dsc*dp*ic*isc*ip*in*
alias: usb:v1A86p5523d*dc*dsc*dp*ic*isc*ip*in*
alias: usb:v1A86p5512d*dc*dsc*dp*ic*isc*ip*in*
depends: usbserial
retpoline: Y
intree: Y
name: ch341
vermagic: 5.4.0-66-generic SMP mod_unload
sig_id: PKCS#7
signer: Build time autogenerated kernel key
sig_key: 1E:07:0D:94:23:77:98:99:05:31:F3:76:E8:6B:76:12:7C:83:9E:05
sig_hashalgo: sha512
signature: 50:CE:79:92:87:EA:82:77:A9:25:A3:B7:F2:B3:ED:63:FE:85:EB:61:
                7A:31:C5:9E:E5:78:E5:44:C6:FE:5D:74:4A:60:B6:0A:94:3F:C3:70:
                0B:6D:27:A6:89:F7:D2:AC:8E:71:AC:0D:AF:5D:3A:19:07:18:F9:7C:
                B8:3C:47:DF:18:4D:13:C9:F8:45:AC:81:19:B0:DE:57:16:1A:F5:C6:
                AC:41:7E:E7:F2:6D:29:9C:14:A3:04:F8:9B:DF:8D:2E:9F:34:44:18:
                A8:FF:C6:A4:AF:04:86:D5:6D:F2:4C:AD:D2:65:4C:63:0F:C1:82:E3:
                28:20:F2:D4:80:86:1A:67:1D:A2:56:18:87:E2:AB:40:E6:6A:48:E5:
                D7:D2:6F:6F:DB:05:20:B2:76:81:5C:0C:36:02:37:E9:A2:08:4E:53:
                5E:9C:18:03:50:11:2D:E4:62:74:6E:CB:42:67:25:22:0C:F6:55:D8:
                6F:E3:5A:15:AC:10:B7:F2:B7:C9:20:6C:19:ED:CC:7D:CC:CB:48:3B:
                B0:5E:E3:ED:05:DF:DF:65:FF:19:AD:76:6E:40:D2:0B:F0:11:65:D5:
                92:7D:C9:3A:32:BE:A8:13:CE:C1:DE:D9:73:0F:0A:0B:8A:08:55:2E:
                41:9D:B9:9A:AD:EC:4C:7D:98:3A:52:38:DF:78:DE:33:F1:14:A2:1B:
                AC:93:FD:30:76:A5:7C:AF:13:16:B8:5E:0B:73:A7:1F:20:E4:54:44:
                07:A2:11:7F:D7:0E:B3:1C:A9:AA:73:76:0E:89:E0:D5:74:39:66:2F:
                E8:14:93:EC:7A:B2:23:E0:CC:77:9F:CD:D9:99:CB:B0:14:21:1C:1F:
                0C:E9:30:B8:C3:55:8F:49:FC:88:5D:EF:20:B9:0E:F2:88:28:5A:93:
                08:4D:2B:76:64:85:D1:E0:1C:9C:4B:86:2C:DB:65:F6:D8:23:A0:8D:
                1B:22:74:0C:B9:41:9E:57:5A:67:4C:CC:1F:E2:43:5F:C2:21:82:E6:
                D4:C1:66:6F:30:54:27:2E:1D:22:8C:65:7F:93:C8:1D:C0:51:F0:7D:
                7A:96:3A:3B:3D:C4:6E:69:DF:83:8A:85:0D:35:15:F9:5E:89:0F:D5:
                9E:6F:A1:5F:39:CE:2A:88:57:97:DF:42:5C:70:12:4E:91:9E:1A:92:
                49:99:C3:7B:38:12:B0:3A:D0:92:38:45:C7:74:3C:66:0F:A1:9C:C2:
                9F:DC:A2:1B:DF:20:BB:F5:A5:F0:10:D6:6F:4F:C1:90:00:C3:F9:D8:
                42:96:D2:28:FD:DE:21:33:6C:F4:7F:18:B2:ED:F9:A6:A4:4A:A5:4F:
                26:7C:C0:F7:8B:A9:B3:2F:5A:5B:E2:B8

Demsg entries:
usb 4-3: new full-speed USB device number 6 using ohci-pci
usb 4-3: New USB device found, idVendor=4348, idProduct=5523, bcdDevice= 2.50
usb 4-3: New USB device strings: Mfr=0, Product=0, SerialNumber=0
ch341 4-3:1.0: ch341-uart converter detected
usb 4-3: ch341-uart converter now attached to ttyUSB0