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Date:   Thu, 30 Aug 2018 10:59:37 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Ezequiel Garcia <ezequiel@collabora.com>
Cc:     linux-media@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Tomasz Figa <tfiga@chromium.org>,
        "Matwey V . Kornilov" <matwey@sai.msu.ru>,
        Alan Stern <stern@rowland.harvard.edu>, kernel@collabora.com,
        Keiichi Watanabe <keiichiw@chromium.org>
Subject: Re: [RFC 3/3] stk1160: Use non-coherent buffers for USB transfers
Message-ID: <20180830175937.GB11521@infradead.org>
References: <20180830172030.23344-1-ezequiel@collabora.com>
 <20180830172030.23344-4-ezequiel@collabora.com>
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> +	dma_sync_single_for_cpu(&urb->dev->dev, urb->transfer_dma,
> +		urb->transfer_buffer_length, DMA_FROM_DEVICE);

You can't ue dma_sync_single_for_cpu on non-coherent dma buffers,
which is one of the major issues with them.