linux-kernel - Re: [PATCH 2/4] i2c: imx: Fix race condition in dma read

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Message-ID: <87tvp8ahm0.fsf@gmail.com>
Date:   Mon, 09 Jul 2018 11:22:31 +0200
From:   Esben Haabendal <esben.haabendal@...il.com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     linux-i2c@...r.kernel.org,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Phil Reid <preid@...ctromag.com.au>,
        Linus Walleij <linus.walleij@...aro.org>,
        Clemens Gruber <clemens.gruber@...ruber.com>,
        Wei Jinhua <wei.jinhua1@....com.cn>,
        Michail Georgios Etairidis <m.etairidis@...k-ipc.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] i2c: imx: Fix race condition in dma read

Uwe Kleine-König <u.kleine-koenig@...gutronix.de> writes:

> On Wed, May 23, 2018 at 11:56:21AM +0200, Esben Haabendal wrote:
>> From: Esben Haabendal <eha@...f.com>
>> 
>> This fixes a race condition, where the DMAEN bit ends up being set after
>> I2C slave has transmitted a byte following the dummy read.  When that
>> happens, an interrupt is generated instead, and no DMA request is generated
>> to kickstart the DMA read, and a timeout happens after DMA_TIMEOUT (1 sec).
>> 
>> Fixed by setting the DMAEN bit before the dummy read.
>
> Does this fix the problem or just narrow the race window?

It should fix the problem.

/Esben