linux-kernel - [PATCH 0/2] fixes for empty tx buffer breakage

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Message-Id: <1404660593-12172-1-git-send-email-peter@hurleysoftware.com>
Date:	Sun,  6 Jul 2014 11:29:51 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>,
	Seth Bollinger <sethb@...i.com>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Sam Ravnborg <sam@...nborg.org>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Subject: [PATCH 0/2] fixes for empty tx buffer breakage

Cc: Seth Bollinger <sethb@...i.com>
Cc: Aaro Koskinen <aaro.koskinen@....fi>
Cc: Sam Ravnborg <sam@...nborg.org>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>

Greg,

I completed the audit of serial drivers after reports that
several Sun serial drivers were broken by
commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c,
'serial_core: Fix conditional start_tx on ring buffer not empty'.

I apologize for not submitting this sooner. The delay was due to
an ongoing analysis of serial flow control prompted by Sam Ravnborg's
question:

On 06/10/2014 03:24 PM, Sam Ravnborg wrote:
> I also noticed the typical pattern is:
> 
>      if (uart_circ_empty(xmit) || uart_tx_stopped(port))
> 
> Should you use this pattern also in sunsab.c?

Unfortunately, that analysis revealed that tx flow control is
largely SMP-unsafe, and it's fairly easy to corrupt the hardware
state wrt. the tty flow control state.

I'm still working on the solutions to that; they're too
extensive to submit for 3.16 anyway.

Regards,

Peter Hurley (2):
  serial: Test for no tx data on tx restart
  serial: arc_uart: Use uart_circ_empty() for open-coded comparison

 drivers/tty/serial/arc_uart.c   | 2 +-
 drivers/tty/serial/imx.c        | 3 +++
 drivers/tty/serial/ip22zilog.c  | 2 ++
 drivers/tty/serial/m32r_sio.c   | 8 +++++---
 drivers/tty/serial/pmac_zilog.c | 3 +++
 drivers/tty/serial/sunsab.c     | 3 +++
 drivers/tty/serial/sunzilog.c   | 2 ++
 7 files changed, 19 insertions(+), 4 deletions(-)

-- 
2.0.0

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