linux-kernel - Re: [PATCH] i2c: mxs: ensure that DMA buffers are safe for DMA

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Message-ID: <ZBNyaVI9ZdvPGPz6@shikoro>
Date:   Thu, 16 Mar 2023 20:47:53 +0100
From:   Wolfram Sang <wsa@...nel.org>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Nicolas Pitre <nico@...xnic.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux@...tq-group.com
Subject: Re: [PATCH] i2c: mxs: ensure that DMA buffers are safe for DMA

On Mon, Feb 13, 2023 at 04:25:50PM +0100, Matthias Schiffer wrote:
> We found that after commit 9c46929e7989
> ("ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems"), the
> PCF85063 RTC driver stopped working on i.MX28 due to regmap_bulk_read()
> reading bogus data into a stack buffer. This is caused by the i2c-mxs
> driver using DMA transfers even for messages without the I2C_M_DMA_SAFE
> flag, and the aforementioned commit enabling vmapped stacks.
> 
> As the MXS I2C controller requires DMA for reads of >4 bytes, DMA can't be
> disabled, so the issue is fixed by using i2c_get_dma_safe_msg_buf() to
> create a bounce buffer when needed.
> 
> Fixes: 9c46929e7989 ("ARM: implement THREAD_INFO_IN_TASK for uniprocessor systems")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>

Applied to for-current, thanks!


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