linux-kernel - Re: [PATCH] i2c: i2c-qcom-geni: Properly handle DMA safe buffers

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Date:   Wed, 19 Sep 2018 00:16:46 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Karthikeyan Ramasubramanian <kramasub@...eaurora.org>,
        Sagar Dharia <sdharia@...eaurora.org>,
        Girish Mahadevan <girishm@...eaurora.org>
Subject: Re: [PATCH] i2c: i2c-qcom-geni: Properly handle DMA safe buffers


> This fixes a problem where the kernel oopses cleaning pages for a buffer
> that's mapped into the vmalloc space. The pages are returned from
> request_firmware() and passed down directly to the i2c master to write
> to the i2c touchscreen device. Mapping vmalloc buffers with
> dma_map_single() won't work reliably, causing an oops like below:

Exactly the reason why I implemented I2C_M_DMA_SAFE. Did you also notice
the helper i2c_get_dma_safe_msg_buf() which you maybe could use for
len > 32?


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