https://bugzilla.kernel.org/show_bug.cgi?id=213771 --- Comment #2 from Luzemario (luzemario@xxxxxxxxx) --- Sorry. Description was copied from former bugtracker to make it self-conteined. Iw was tested within Ubuntu and Alpine, with Linuz original kernel. Please ignore Ubuntu-specific information. ********* This device works flawlessly on Windows XP with native driver, both as a physical machine or inside a VM. It appears on XP's device management as "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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emsg 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 --- ProblemType: Bug ApportVersion: 2.20.11-0ubuntu27.16 Architecture: amd64 [...] # not relevant / stripped DistroRelease: Ubuntu 20.04 InstallationDate: Installed on 2021-01-23 (50 days ago) InstallationMedia: Kubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731) MachineType: System manufacturer System Product Name NonfreeKernelModules: nvidia_modeset nvidia Package: linux (not installed) ProcFB: 0 VESA VGA ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-66-generic root=UUID=68929bb0-3af4-4634-8d5b-c2846910c077 ro locale=pt_BR quiet splash vt.handoff=7 ProcVersionSignature: Ubuntu 5.4.0-66.74-generic 5.4.86 RelatedPackageVersions: linux-restricted-modules-5.4.0-66-generic N/A linux-backports-modules-5.4.0-66-generic N/A linux-firmware 1.187.10 RfKill: Tags: focal Uname: Linux 5.4.0-66-generic x86_64 UpgradeStatus: No upgrade log present (probably fresh install) UserGroups: adm cdrom dip libvirt lpadmin lxd plugdev sambashare sudo _MarkForUpload: True dmi.bios.date: 11/18/2016 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 0502 dmi.board.asset.tag: To Be Filled By O.E.M. dmi.board.name: M5A78L-M PLUS/USB3 dmi.board.vendor: ASUSTeK Computer INC. dmi.board.version: Rev X.0x dmi.chassis.asset.tag: Asset-1234567890 dmi.chassis.type: 3 dmi.chassis.vendor: Chassis Manufacture dmi.chassis.version: Chassis Version dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0502:bd11/18/2016:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnM5A78L-MPLUS/USB3:rvrRevX.0x:cvnChassisManufacture:ct3:cvrChassisVersion: dmi.product.family: To Be Filled By O.E.M. dmi.product.name: System Product Name dmi.product.sku: To Be Filled By O.E.M. dmi.product.version: System Version dmi.sys.vendor: System manufacturer -- You may reply to this email to add a comment. 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