From mboxrd@z Thu Jan  1 00:00:00 1970
From: nicolas.ferre@atmel.com (Nicolas Ferre)
Date: Fri, 5 Sep 2014 14:48:00 +0200
Subject: [PATCH] tty/serial: at91: BUG: disable interrupts when
 !UART_ENABLE_MS()
In-Reply-To: <54099926.6000302@hurleysoftware.com>
References: <1409760567-13186-1-git-send-email-richard.genoud@gmail.com>
 <54097F2E.6090809@atmel.com> <54099926.6000302@hurleysoftware.com>
Message-ID: <5409B100.5080709@atmel.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 05/09/2014 13:06, Peter Hurley :
> Hi Nicolas,
> 
> On 09/05/2014 05:15 AM, Nicolas Ferre wrote:
>> On 03/09/2014 18:09, Richard Genoud :
>> Richard,
>>
>> Indeed it seems needed:
>>
>> Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
>>
>>
>> But BTW, I see just below a call to the atmel_enable_ms() function in
>> atmel_set_ldisc(). My question is, shouldn't we also add this
>> atmel_disable_ms() in the alternative that disables the PPS in this
>> ldisc function?
> 
> I have that change in another series but it has to wait for:

Given the attractive enhancements that you describe below... I'll wait
with pleasure ;-)

> 1. another series that fixes races setting and clearing the controlling tty
>    (and reduces the footprint of tty_mutex)
> 2. a series built on that which moves tty_lock() out from under tty_mutex
>    when reopening ttys
>    This allows the tty_lock to be held while closing the tty.
> 3. a series which removes the ldisc flush from the serial core, among some
>    other locking fixes in the serial core.
>    This fixes a lock inversion between the termios_rwsem and the port mutex.
> 
> All of which enables the set_ldisc() notification to be safely passed
> termios so it can use UART_ENABLE_MS() and also claim the port mutex
> to change the UPF_HARDPPS_CD flag, which is currently non-atomic and
> may corrupt the uart port flags field.
> 
> The series also claims the port lock around the *_enable_ms() in the
> various set_ldisc() handlers to protect the hardware re-programming :)
> 
> Right now, all of this is temporarily stuck on the most recent patch
> series, which hinges on whether the kernel should continue to support
> non-atomic byte stores.

Thanks for sharing your plans. Bye,
-- 
Nicolas Ferre