[Bug 213771] ch341 USB-Serial converter receives but does not send

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=213771

--- Comment #4 from Johan Hovold (johan@kernel.org) ---
On Wed, Jul 21, 2021 at 07:00:08PM +0000, bugzilla-daemon@bugzilla.kernel.org
wrote:

> 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.

What happens if you also short RTS and CTS?

And are you able to change the baud rate at all?

> 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

Please confirm using a recent mainline kernel (e.g. 5.13).

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

This looks strange. I don't think these devices are based on
(misspelled) Prolific PL2303 chips.

This is possibly some kind of counterfeit device. You could try using
the pl2303 driver.

Please also post the output of lsusb -v.

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