linux-kernel - Broken serial port

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Date:	Tue, 17 Jun 2014 20:48:04 +0200
From:	Laurent Vivier <Laurent@...ier.EU>
To:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	Jiri Slaby <jslaby@...e.cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Seth Bollinger <sethb@...i.com>
Subject: Broken serial port

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.

A little demo :

http://asciinema.org/a/10211 [at 3:20]

I bisect and I found this commit :

commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c
Author: Seth Bollinger <sethb@...i.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@...i.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>


If I revert it, all works fine :

http://asciinema.org/a/10212

Regards,
Laurent


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