Re: Broken serial port

[Peter Hurley <peter@hurleysoftware.com>]

On 06/17/2014 02:48 PM, Laurent Vivier wrote:
> Hi,
>
> I'm not subscribed to these mailing lists, so CC: me.
>
> I'm playing for some days with a kernel 3.15 on an old mac performa 575
> and it seems that the serial port is broken. When I log on using the
> console on the serial port it seems there is an screen refresh added
> after each character I send.

What uart driver is this happening on?

This is a known bug being worked on for these uart drivers:
sunsab
sunzilog
ip22zilog
pmac_zilog

Regards,
Peter Hurley

> A little demo :
>
> http://asciinema.org/a/10211 [at 3:20]
>
> I bisect and I found this commit :
>
> commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c
> Author: Seth Bollinger <sethb@digi.com>
> Date:   Tue Mar 25 12:55:37 2014 -0500
>
>      serial_core: Fix conditional start_tx on ring buffer not empty
>
>      If the serial_core ring buffer empties just as the tty layer receives
>      an XOFF, then start_tx will never be called when the tty layer
>      receives an XON as the serial_core ring buffer is empty.  This will
>      possibly leave a few bytes trapped in the fifo for drivers that
>      disable the transmitter when flow controlled.
>
>      Signed-off-by: Seth Bollinger <sethb@digi.com>
>      Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
>
> If I revert it, all works fine :
>
> http://asciinema.org/a/10212
>
> Regards,
> Laurent
>