[Bug 208959] USB-serial (mct_u232): bit7=1 when tty is set to cs7?

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=208959

--- Comment #1 from Johan Hovold (johan@kernel.org) ---
On Wed, Aug 19, 2020 at 02:52:47AM +0000, bugzilla-daemon@bugzilla.kernel.org
wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=208959
> 
>             Bug ID: 208959
>            Summary: USB-serial (mct_u232): bit7=1 when tty is set to cs7?
>            Product: Drivers
>            Version: 2.5
>     Kernel Version: 5.7.0
>           Hardware: All
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: low
>           Priority: P1
>          Component: USB
>           Assignee: drivers_usb@kernel-bugs.kernel.org
>           Reporter: mslade@epic-code.com.au
>         Regression: No
> 
> I'm not 100% certain this is a bug, please let me know if this is expected
> behavior.
> 
> I have hooked an old serial mouse up to a USB serial device, USB ID 0711:0230
> (part of an circa 2000 Targus port replicator)
> 
> when I configure it with the appropriate 1200 baud and 7 bit char width, the
> bytes that come through /dev/ttyUSB0 all have bit7 set to 1.
> 
> This behavior is in contrast to an old serial port on a box running a 2.4.19
> kernel.
> 
> Is there a standard for the value that non-data bits should be set to?

This sounds like a configuration issue. If the mouse is indeed using
7n1 and the converter is expecting 8n1 you could end up with bit 7
always set on input.

Can you verify that the converter is configured correctly, for example,
by reading out the termios settings, enabling debugging and/or
connecting it to another serial port configured for 7n1?

Johan

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